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Persistent static routes fail on MacOS 10.6.5 startup!

- by verbalicious

I'm unable to get static routes to persist a reboot on Mac OS 10.6.5. I've tried all of the methods prescribed in Google search results, and previous posts on this site. I've tried manually creating a launchd daemon, and used RouteSplit's launchd daemon to no avail. It's clear that the interface is not ready when these methods attempt to apply the route. This workstation in question is getting its IP from DHCP and probably hasn't gotten its DHCP lease when the command runs. We're able to apply the route by hand when logged in, but not through startup methods. Is there another way to apply this route by sneaking the command into something later, but before the login window appears to the user? Here is some relevant log info from system.log. You can see the "route: writing to routing socket: Network is unreachable" errors where my launchd script fires off. I've tried adding extra "sleep" and "ipconfig waitall" statements later in the script but this doesn't fly. Dec 15 19:30:41 localhost com.apple.launchd[1]: *** launchd[1] has started up. *** Dec 15 19:30:45 localhost mDNSResponder[18]: mDNSResponder mDNSResponder-258.13 (Oct 8 2010 17:10:30) starting Dec 15 19:30:47 localhost configd[15]: bootp_session_transmit: bpf_write(en1) failed: Network is down (50) Dec 15 19:30:47 localhost configd[15]: DHCP en1: INIT transmit failed Dec 15 19:30:47 localhost configd[15]: network configuration changed. Dec 15 19:30:47 Administrators-MacBook-Pro configd[15]: setting hostname to "Administrators-MacBook-Pro.local" Dec 15 19:30:47 Administrators-MacBook-Pro blued[16]: Apple Bluetooth daemon started Dec 15 19:30:52 Administrators-MacBook-Pro syslog[67]: routes.sh: Starting RouteSplit Dec 15 19:30:53 Administrators-MacBook-Pro com.apple.usbmuxd[41]: usbmuxd-207 built for iTunesTenOne on Oct 19 2010 at 13:50:35, running 64 bit Dec 15 19:30:54 Administrators-MacBook-Pro /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow[50]: Login Window Application Started Dec 15 19:30:55 Administrators-MacBook-Pro bootlog[61]: BOOT_TIME: 1292459441 0 Dec 15 19:30:55 Administrators-MacBook-Pro syslog[86]: routes.sh: static route 192.168.0.0/23 192.168.2.2 Dec 15 19:30:55 Administrators-MacBook-Pro net.routes.static[65]: route: writing to routing socket: Network is unreachable Dec 15 19:30:55 Administrators-MacBook-Pro net.routes.static[65]: add net 192.168.0.0: gateway 192.168.2.2: Network is unreachable Dec 15 19:30:57 Administrators-MacBook-Pro org.apache.httpd[38]: httpd: Could not reliably determine the server's fully qualified domain name, using Administrators-MacBook-Pro.local for ServerName Dec 15 19:30:58 Administrators-MacBook-Pro loginwindow[50]: Login Window Started Security Agent Dec 15 19:30:58 Administrators-MacBook-Pro WindowServer[89]: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged. Dec 15 19:30:58 Administrators-MacBook-Pro com.apple.WindowServer[89]: Wed Dec 15 19:30:58 Administrators-MacBook-Pro.local WindowServer[89] <Error>: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged. Dec 15 19:31:18 Administrators-MacBook-Pro configd[15]: network configuration changed. Dec 15 19:31:19 administrators-macbook-pro configd[15]: setting hostname to "administrators-macbook-pro.local" Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[121]: /usr/libexec/ntpd-wrapper: scutil key State:/Network/Global/DNS not present after 30 seconds Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: sntp options: a=2 v=1 e=0.100 E=5.000 P=2147483647.000 Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: d=15 c=5 x=0 op=1 l=/var/run/sntp.pid f= time.apple.com Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: sntp: getaddrinfo(hostname, ntp) failed with nodename nor servname provided, or not known Dec 15 19:31:27 administrators-macbook-pro configd[15]: network configuration changed. Dec 15 19:31:27 Administrators-MacBook-Pro configd[15]: setting hostname to "Administrators-MacBook-Pro.local" Dec 15 19:31:27 Administrators-MacBook-Pro ntpd[37]: Cannot find existing interface for address 17.151.16.20 Dec 15 19:31:27 Administrators-MacBook-Pro ntpd_initres[125]: ntpd indicates no data available! Dec 15 19:31:31 Administrators-MacBook-Pro sshd[128]: USER_PROCESS: 133 ttys000 Dec 15 19:31:37 Administrators-MacBook-Pro sudo[138]: administrator : TTY=ttys000 ; PWD=/Users/administrator ; USER=root ; COMMAND=/usr/bin/less /var/log/system.log ``You can see the following line in /var/log/kernel.log that shows the en0 interface coming up: Dec 15 19:30:51 Administrators-MacBook-Pro kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, No flow-control, Debug [796d,0f01,0de1,0300,c1e1,3800]

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Persistent static routes fail on MacOS 10.6.5 startup!

- by verbalicious

I'm unable to get static routes to persist a reboot on Mac OS 10.6.5. I've tried all of the methods prescribed in Google search results, and previous posts on this site. I've tried manually creating a launchd daemon, and used RouteSplit's launchd daemon to no avail. It's clear that the interface is not ready when these methods attempt to apply the route. This workstation in question is getting its IP from DHCP and probably hasn't gotten its DHCP lease when the command runs. We're able to apply the route by hand when logged in, but not through startup methods. Is there another way to apply this route by sneaking the command into something later, but before the login window appears to the user? Here is some relevant log info from system.log. You can see the "route: writing to routing socket: Network is unreachable" errors where my launchd script fires off. I've tried adding extra "sleep" and "ipconfig waitall" statements later in the script but this doesn't fly. Dec 15 19:30:41 localhost com.apple.launchd[1]: *** launchd[1] has started up. *** Dec 15 19:30:45 localhost mDNSResponder[18]: mDNSResponder mDNSResponder-258.13 (Oct 8 2010 17:10:30) starting Dec 15 19:30:47 localhost configd[15]: bootp_session_transmit: bpf_write(en1) failed: Network is down (50) Dec 15 19:30:47 localhost configd[15]: DHCP en1: INIT transmit failed Dec 15 19:30:47 localhost configd[15]: network configuration changed. Dec 15 19:30:47 Administrators-MacBook-Pro configd[15]: setting hostname to "Administrators-MacBook-Pro.local" Dec 15 19:30:47 Administrators-MacBook-Pro blued[16]: Apple Bluetooth daemon started Dec 15 19:30:52 Administrators-MacBook-Pro syslog[67]: routes.sh: Starting RouteSplit Dec 15 19:30:53 Administrators-MacBook-Pro com.apple.usbmuxd[41]: usbmuxd-207 built for iTunesTenOne on Oct 19 2010 at 13:50:35, running 64 bit Dec 15 19:30:54 Administrators-MacBook-Pro /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow[50]: Login Window Application Started Dec 15 19:30:55 Administrators-MacBook-Pro bootlog[61]: BOOT_TIME: 1292459441 0 Dec 15 19:30:55 Administrators-MacBook-Pro syslog[86]: routes.sh: static route 192.168.0.0/23 192.168.2.2 Dec 15 19:30:55 Administrators-MacBook-Pro net.routes.static[65]: route: writing to routing socket: Network is unreachable Dec 15 19:30:55 Administrators-MacBook-Pro net.routes.static[65]: add net 192.168.0.0: gateway 192.168.2.2: Network is unreachable Dec 15 19:30:57 Administrators-MacBook-Pro org.apache.httpd[38]: httpd: Could not reliably determine the server's fully qualified domain name, using Administrators-MacBook-Pro.local for ServerName Dec 15 19:30:58 Administrators-MacBook-Pro loginwindow[50]: Login Window Started Security Agent Dec 15 19:30:58 Administrators-MacBook-Pro WindowServer[89]: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged. Dec 15 19:30:58 Administrators-MacBook-Pro com.apple.WindowServer[89]: Wed Dec 15 19:30:58 Administrators-MacBook-Pro.local WindowServer[89] <Error>: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged. Dec 15 19:31:18 Administrators-MacBook-Pro configd[15]: network configuration changed. Dec 15 19:31:19 administrators-macbook-pro configd[15]: setting hostname to "administrators-macbook-pro.local" Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[121]: /usr/libexec/ntpd-wrapper: scutil key State:/Network/Global/DNS not present after 30 seconds Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: sntp options: a=2 v=1 e=0.100 E=5.000 P=2147483647.000 Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: d=15 c=5 x=0 op=1 l=/var/run/sntp.pid f= time.apple.com Dec 15 19:31:25 administrators-macbook-pro _mdnsresponder[124]: sntp: getaddrinfo(hostname, ntp) failed with nodename nor servname provided, or not known Dec 15 19:31:27 administrators-macbook-pro configd[15]: network configuration changed. Dec 15 19:31:27 Administrators-MacBook-Pro configd[15]: setting hostname to "Administrators-MacBook-Pro.local" Dec 15 19:31:27 Administrators-MacBook-Pro ntpd[37]: Cannot find existing interface for address 17.151.16.20 Dec 15 19:31:27 Administrators-MacBook-Pro ntpd_initres[125]: ntpd indicates no data available! Dec 15 19:31:31 Administrators-MacBook-Pro sshd[128]: USER_PROCESS: 133 ttys000 Dec 15 19:31:37 Administrators-MacBook-Pro sudo[138]: administrator : TTY=ttys000 ; PWD=/Users/administrator ; USER=root ; COMMAND=/usr/bin/less /var/log/system.log ``You can see the following line in /var/log/kernel.log that shows the en0 interface coming up: Dec 15 19:30:51 Administrators-MacBook-Pro kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, No flow-control, Debug [796d,0f01,0de1,0300,c1e1,3800]

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why nginx rewrite post request from /login to //login?

- by jiangchengwu

There is a if statement, which will rewrite url when the client is Android. Everything ok. But, something got strange. Nginx will write post request /login to //login, even if the block of if statement is bank. So I got a 404 page. As the jetty server only accept /login request. Server conf: location / { proxy_pass http://localhost:8785/; proxy_set_header Host $http_host; proxy_set_header Remote-Addr $http_remote_addr; proxy_set_header X-Real-IP $remote_addr; if ( $http_user_agent ~ Android ){ # rewrite something, been commented } } Debug info, origin log https://gist.github.com/3799021 ... 2012/09/28 16:29:49 [debug] 26416#0: *1 http script regex: "Android" 2012/09/28 16:29:49 [notice] 26416#0: *1 "Android" matches "Android/1.0", client: 106.187.97.22, server: ireedr.com, request: "POST /login HTTP/1.1", host: "ireedr.com" ... 2012/09/28 16:29:49 [debug] 26416#0: *1 http proxy header: "POST //login HTTP/1.0 Host: ireedr.com X-Real-IP: 106.187.97.22 Connection: close Accept-Encoding: identity, deflate, compress, gzip Accept: */* User-Agent: Android/1.0 " ... 2012/09/28 16:29:49 [debug] 26416#0: *1 HTTP/1.1 404 Not Found Server: nginx/1.2.1 Date: Fri, 28 Sep 2012 08:29:49 GMT Content-Type: text/html;charset=ISO-8859-1 Transfer-Encoding: chunked Connection: keep-alive Cache-Control: must-revalidate,no-cache,no-store Content-Encoding: gzip ... Only when I commented the block in the configration file: location / { proxy_pass http://localhost:8785/; proxy_set_header Host $http_host; proxy_set_header Remote-Addr $http_remote_addr; proxy_set_header X-Real-IP $remote_addr; #if ( $http_user_agent ~ Android ){ # #} } The client can get an 200 response. Debug info, origin log https://gist.github.com/3799023 ... "POST /login HTTP/1.0 Host: ireedr.com X-Real-IP: 106.187.97.22 Connection: close Accept-Encoding: identity, deflate, compress, gzip Accept: */* User-Agent: Android/1.0 " ... 2012/09/28 16:27:19 [debug] 26319#0: *1 HTTP/1.1 200 OK Server: nginx/1.2.1 Date: Fri, 28 Sep 2012 08:27:19 GMT Content-Type: application/json;charset=UTF-8 Content-Length: 17 Connection: keep-alive ... As the log: 2012/09/28 16:29:49 [notice] 26416#0: *1 "Android" matches "Android/1.0", client: 106.187.97.22, server: ireedr.com, request: "POST /login HTTP/1.1", host: "ireedr.com" 2012/09/28 16:29:49 [debug] 26416#0: *1 http script if 2012/09/28 16:29:49 [debug] 26416#0: *1 post rewrite phase: 4 2012/09/28 16:29:49 [debug] 26416#0: *1 generic phase: 5 2012/09/28 16:29:49 [debug] 26416#0: *1 generic phase: 6 2012/09/28 16:29:49 [debug] 26416#0: *1 generic phase: 7 2012/09/28 16:29:49 [debug] 26416#0: *1 access phase: 8 2012/09/28 16:29:49 [debug] 26416#0: *1 access phase: 9 2012/09/28 16:29:49 [debug] 26416#0: *1 access phase: 10 2012/09/28 16:29:49 [debug] 26416#0: *1 post access phase: 11 2012/09/28 16:29:49 [debug] 26416#0: *1 try files phase: 12 2012/09/28 16:29:49 [debug] 26416#0: *1 posix_memalign: 0000000001E798F0:4096 @16 2012/09/28 16:29:49 [debug] 26416#0: *1 http init upstream, client timer: 0 2012/09/28 16:29:49 [debug] 26416#0: *1 epoll add event: fd:13 op:3 ev:80000005 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: "Host: " 2012/09/28 16:29:49 [debug] 26416#0: *1 http script var: "ireedr.com" 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: " " 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: "" 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: "" 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: "X-Real-IP: " 2012/09/28 16:29:49 [debug] 26416#0: *1 http script var: "106.187.97.22" 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: " " 2012/09/28 16:29:49 [debug] 26416#0: *1 http script copy: "Connection: close " 2012/09/28 16:29:49 [debug] 26416#0: *1 http proxy header: "Accept-Encoding: identity, deflate, compress, gzip" 2012/09/28 16:29:49 [debug] 26416#0: *1 http proxy header: "Accept: */*" 2012/09/28 16:29:49 [debug] 26416#0: *1 http proxy header: "User-Agent: Android/1.0" 2012/09/28 16:29:49 [debug] 26416#0: *1 http proxy header: "POST //login HTTP/1.0 Host: ireedr.com X-Real-IP: 106.187.97.22 Connection: close Accept-Encoding: identity, deflate, compress, gzip Accept: */* User-Agent: Android/1.0 " ... Maybe post rewrite phase had rewrite the request. Anybody can help me to solve this problem or know why nginx do that ? Much appreciated.

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Parallelism in .NET – Part 14, The Different Forms of Task

- by Reed

Before discussing Task creation and actual usage in concurrent environments, I will briefly expand upon my introduction of the Task class and provide a short explanation of the distinct forms of Task. The Task Parallel Library includes four distinct, though related, variations on the Task class. In my introduction to the Task class, I focused on the most basic version of Task. This version of Task, the standard Task class, is most often used with an Action delegate. This allows you to implement for each task within the task decomposition as a single delegate. Typically, when using the new threading constructs in .NET 4 and the Task Parallel Library, we use lambda expressions to define anonymous methods. The advantage of using a lambda expression is that it allows the Action delegate to directly use variables in the calling scope. This eliminates the need to make separate Task classes for Action<T>, Action<T1,T2>, and all of the other Action<…> delegate types. As an example, suppose we wanted to make a Task to handle the ”Show Splash” task from our earlier decomposition. Even if this task required parameters, such as a message to display, we could still use an Action delegate specified via a lambda: // Store this as a local variable string messageForSplashScreen = GetSplashScreenMessage(); // Create our task Task showSplashTask = new Task( () => { // We can use variables in our outer scope, // as well as methods scoped to our class! this.DisplaySplashScreen(messageForSplashScreen); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This provides a huge amount of flexibility. We can use this single form of task for any task which performs an operation, provided the only information we need to track is whether the task has completed successfully or not. This leads to my first observation: Use a Task with a System.Action delegate for any task for which no result is generated. This observation leads to an obvious corollary: we also need a way to define a task which generates a result. The Task Parallel Library provides this via the Task<TResult> class. Task<TResult> subclasses the standard Task class, providing one additional feature – the ability to return a value back to the user of the task. This is done by switching from providing an Action delegate to providing a Func<TResult> delegate. If we decompose our problem, and we realize we have one task where its result is required by a future operation, this can be handled via Task<TResult>. For example, suppose we want to make a task for our “Check for Update” task, we could do: Task<bool> checkForUpdateTask = new Task<bool>( () => { return this.CheckWebsiteForUpdate(); }); Later, we would start this task, and perform some other work. At any point in the future, we could get the value from the Task<TResult>.Result property, which will cause our thread to block until the task has finished processing: // This uses Task<bool> checkForUpdateTask generated above... // Start the task, typically on a background thread checkForUpdateTask.Start(); // Do some other work on our current thread this.DoSomeWork(); // Discover, from our background task, whether an update is available // This will block until our task completes bool updateAvailable = checkForUpdateTask.Result; This leads me to my second observation: Use a Task<TResult> with a System.Func<TResult> delegate for any task which generates a result. Task and Task<TResult> provide a much cleaner alternative to the previous Asynchronous Programming design patterns in the .NET framework. Instead of trying to implement IAsyncResult, and providing BeginXXX() and EndXXX() methods, implementing an asynchronous programming API can be as simple as creating a method that returns a Task or Task<TResult>. The client side of the pattern also is dramatically simplified – the client can call a method, then either choose to call task.Wait() or use task.Result when it needs to wait for the operation’s completion. While this provides a much cleaner model for future APIs, there is quite a bit of infrastructure built around the current Asynchronous Programming design patterns. In order to provide a model to work with existing APIs, two other forms of Task exist. There is a constructor for Task which takes an Action<Object> and a state parameter. In addition, there is a constructor for creating a Task<TResult> which takes a Func<Object, TResult> as well as a state parameter. When using these constructors, the state parameter is stored in the Task.AsyncState property. While these two overloads exist, and are usable directly, I strongly recommend avoiding this for new development. The two forms of Task which take an object state parameter exist primarily for interoperability with traditional .NET Asynchronous Programming methodologies. Using lambda expressions to capture variables from the scope of the creator is a much cleaner approach than using the untyped state parameters, since lambda expressions provide full type safety without introducing new variables.

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Parallelism in .NET – Part 15, Making Tasks Run: The TaskScheduler

- by Reed

In my introduction to the Task class, I specifically made mention that the Task class does not directly provide it’s own execution. In addition, I made a strong point that the Task class itself is not directly related to threads or multithreading. Rather, the Task class is used to implement our decomposition of tasks. Once we’ve implemented our tasks, we need to execute them. In the Task Parallel Library, the execution of Tasks is handled via an instance of the TaskScheduler class. The TaskScheduler class is an abstract class which provides a single function: it schedules the tasks and executes them within an appropriate context. This class is the class which actually runs individual Task instances. The .NET Framework provides two (internal) implementations of the TaskScheduler class. Since a Task, based on our decomposition, should be a self-contained piece of code, parallel execution makes sense when executing tasks. The default implementation of the TaskScheduler class, and the one most often used, is based on the ThreadPool. This can be retrieved via the TaskScheduler.Default property, and is, by default, what is used when we just start a Task instance with Task.Start(). Normally, when a Task is started by the default TaskScheduler, the task will be treated as a single work item, and run on a ThreadPool thread. This pools tasks, and provides Task instances all of the advantages of the ThreadPool, including thread pooling for reduced resource usage, and an upper cap on the number of work items. In addition, .NET 4 brings us a much improved thread pool, providing work stealing and reduced locking within the thread pool queues. By using the default TaskScheduler, our Tasks are run asynchronously on the ThreadPool. There is one notable exception to my above statements when using the default TaskScheduler. If a Task is created with the TaskCreationOptions set to TaskCreationOptions.LongRunning, the default TaskScheduler will generate a new thread for that Task, at least in the current implementation. This is useful for Tasks which will persist for most of the lifetime of your application, since it prevents your Task from starving the ThreadPool of one of it’s work threads. The Task Parallel Library provides one other implementation of the TaskScheduler class. In addition to providing a way to schedule tasks on the ThreadPool, the framework allows you to create a TaskScheduler which works within a specified SynchronizationContext. This scheduler can be retrieved within a thread that provides a valid SynchronizationContext by calling the TaskScheduler.FromCurrentSynchronizationContext() method. This implementation of TaskScheduler is intended for use with user interface development. Windows Forms and Windows Presentation Foundation both require any access to user interface controls to occur on the same thread that created the control. For example, if you want to set the text within a Windows Forms TextBox, and you’re working on a background thread, that UI call must be marshaled back onto the UI thread. The most common way this is handled depends on the framework being used. In Windows Forms, Control.Invoke or Control.BeginInvoke is most often used. In WPF, the equivelent calls are Dispatcher.Invoke or Dispatcher.BeginInvoke. As an example, say we’re working on a background thread, and we want to update a TextBlock in our user interface with a status label. The code would typically look something like: // Within background thread work... string status = GetUpdatedStatus(); Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action( () => { statusLabel.Text = status; })); // Continue on in background method .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This works fine, but forces your method to take a dependency on WPF or Windows Forms. There is an alternative option, however. Both Windows Forms and WPF, when initialized, setup a SynchronizationContext in their thread, which is available on the UI thread via the SynchronizationContext.Current property. This context is used by classes such as BackgroundWorker to marshal calls back onto the UI thread in a framework-agnostic manner. The Task Parallel Library provides the same functionality via the TaskScheduler.FromCurrentSynchronizationContext() method. When setting up our Tasks, as long as we’re working on the UI thread, we can construct a TaskScheduler via: TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); We then can use this scheduler on any thread to marshal data back onto the UI thread. For example, our code above can then be rewritten as: string status = GetUpdatedStatus(); (new Task(() => { statusLabel.Text = status; })) .Start(uiScheduler); // Continue on in background method This is nice since it allows us to write code that isn’t tied to Windows Forms or WPF, but is still fully functional with those technologies. I’ll discuss even more uses for the SynchronizationContext based TaskScheduler when I demonstrate task continuations, but even without continuations, this is a very useful construct. In addition to the two implementations provided by the Task Parallel Library, it is possible to implement your own TaskScheduler. The ParallelExtensionsExtras project within the Samples for Parallel Programming provides nine sample TaskScheduler implementations. These include schedulers which restrict the maximum number of concurrent tasks, run tasks on a single threaded apartment thread, use a new thread per task, and more.

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Parallelism in .NET – Part 6, Declarative Data Parallelism

- by Reed

When working with a problem that can be decomposed by data, we have a collection, and some operation being performed upon the collection. I’ve demonstrated how this can be parallelized using the Task Parallel Library and imperative programming using imperative data parallelism via the Parallel class. While this provides a huge step forward in terms of power and capabilities, in many cases, special care must still be given for relative common scenarios. C# 3.0 and Visual Basic 9.0 introduced a new, declarative programming model to .NET via the LINQ Project. When working with collections, we can now write software that describes what we want to occur without having to explicitly state how the program should accomplish the task. By taking advantage of LINQ, many operations become much shorter, more elegant, and easier to understand and maintain. Version 4.0 of the .NET framework extends this concept into the parallel computation space by introducing Parallel LINQ. Before we delve into PLINQ, let’s begin with a short discussion of LINQ. LINQ, the extensions to the .NET Framework which implement language integrated query, set, and transform operations, is implemented in many flavors. For our purposes, we are interested in LINQ to Objects. When dealing with parallelizing a routine, we typically are dealing with in-memory data storage. More data-access oriented LINQ variants, such as LINQ to SQL and LINQ to Entities in the Entity Framework fall outside of our concern, since the parallelism there is the concern of the data base engine processing the query itself. LINQ (LINQ to Objects in particular) works by implementing a series of extension methods, most of which work on IEnumerable<T>. The language enhancements use these extension methods to create a very concise, readable alternative to using traditional foreach statement. For example, let’s revisit our minimum aggregation routine we wrote in Part 4: double min = double.MaxValue; foreach(var item in collection) { double value = item.PerformComputation(); min = System.Math.Min(min, value); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, we’re doing a very simple computation, but writing this in an imperative style. This can be loosely translated to English as: Create a very large number, and save it in min Loop through each item in the collection. For every item: Perform some computation, and save the result If the computation is less than min, set min to the computation Although this is fairly easy to follow, it’s quite a few lines of code, and it requires us to read through the code, step by step, line by line, in order to understand the intention of the developer. We can rework this same statement, using LINQ: double min = collection.Min(item => item.PerformComputation()); Here, we’re after the same information. However, this is written using a declarative programming style. When we see this code, we’d naturally translate this to English as: Save the Min value of collection, determined via calling item.PerformComputation() That’s it – instead of multiple logical steps, we have one single, declarative request. This makes the developer’s intentions very clear, and very easy to follow. The system is free to implement this using whatever method required. Parallel LINQ (PLINQ) extends LINQ to Objects to support parallel operations. This is a perfect fit in many cases when you have a problem that can be decomposed by data. To show this, let’s again refer to our minimum aggregation routine from Part 4, but this time, let’s review our final, parallelized version: // Safe, and fast! double min = double.MaxValue; // Make a "lock" object object syncObject = new object(); Parallel.ForEach( collection, // First, we provide a local state initialization delegate. () => double.MaxValue, // Next, we supply the body, which takes the original item, loop state, // and local state, and returns a new local state (item, loopState, localState) => { double value = item.PerformComputation(); return System.Math.Min(localState, value); }, // Finally, we provide an Action<TLocal>, to "merge" results together localState => { // This requires locking, but it's only once per used thread lock(syncObj) min = System.Math.Min(min, localState); } ); Here, we’re doing the same computation as above, but fully parallelized. Describing this in English becomes quite a feat: Create a very large number, and save it in min Create a temporary object we can use for locking Call Parallel.ForEach, specifying three delegates For the first delegate: Initialize a local variable to hold the local state to a very large number For the second delegate: For each item in the collection, perform some computation, save the result If the result is less than our local state, save the result in local state For the final delegate: Take a lock on our temporary object to protect our min variable Save the min of our min and local state variables Although this solves our problem, and does it in a very efficient way, we’ve created a set of code that is quite a bit more difficult to understand and maintain. PLINQ provides us with a very nice alternative. In order to use PLINQ, we need to learn one new extension method that works on IEnumerable<T> – ParallelEnumerable.AsParallel(). That’s all we need to learn in order to use PLINQ: one single method. We can write our minimum aggregation in PLINQ very simply: double min = collection.AsParallel().Min(item => item.PerformComputation()); By simply adding “.AsParallel()” to our LINQ to Objects query, we converted this to using PLINQ and running this computation in parallel! This can be loosely translated into English easily, as well: Process the collection in parallel Get the Minimum value, determined by calling PerformComputation on each item Here, our intention is very clear and easy to understand. We just want to perform the same operation we did in serial, but run it “as parallel”. PLINQ completely extends LINQ to Objects: the entire functionality of LINQ to Objects is available. By simply adding a call to AsParallel(), we can specify that a collection should be processed in parallel. This is simple, safe, and incredibly useful.

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Twitter traffic might not be what it seems

- by Piet

Are you using bit.ly stats to measure interest in the links you post on twitter? I’ve been hearing for a while about people claiming to get the majority of their traffic originating from twitter these days. Now, I’ve been playing with the twitter ruby gem recently, doing various experiments which I’ll not go into detail here because they could be regarded as spamming… if I’d conduct them on a large scale, that is. It’s scary to see people actually engaging with @replies crafted with some regular expressions and eliza-like trickery on status updates found using the twitter api. I’m wondering how Twitter is going to contain the coming spam-flood. When posting links I used bit.ly as url shortener, since this one seems to be the de-facto standard on twitter. A nice thing about bit.ly is that it shows some basic stats about the redirects it performs for your shortened links. To my surprise, most links posted almost immediately resulted in several visitors. Now, seeing that I was posting the links together with some information concerning what the link is about, I concluded that the people who were actually clicking the links should be very targeted visitors. This felt a bit like free adwords, and I suddenly started to understand why everyone was raving about getting traffic from twitter. How wrong I was! (and I think several 1000 online marketers with me) On the destination site I used a traffic logging solution that works by including a little javascript snippet in your pages. It seemed that somehow all visitors disappeared after the bit.ly redirect and before getting to the site, because I was hardly seeing any visitors there. So I started investigating what was happening: by looking at the logfiles of the destination site, and by making my own ’shortened’ urls by doing redirects using a very short domain name I own. This way, I could check the apache access_log before the redirects. Most user agents turned out to be bots without a doubt. Here’s an excerpt of user-agents awk’ed from apache’s access_log for a time period of about one hour, right after posting some links: AideRSS 2.0 (postrank.com) Java/1.6.0_13 Java/1.6.0_14 libwww-perl/5.816 MLBot (www.metadatalabs.com/mlbot) Mozilla/4.0 (compatible;MSIE 5.01; Windows -NT 5.0 - real-url.org) Mozilla/5.0 (compatible; Twitturls; +http://twitturls.com) Mozilla/5.0 (compatible; Viralheat Bot/1.0; +http://www.viralheat.com/) Mozilla/5.0 (Danger hiptop 4.6; U; rv:1.7.12) Gecko/20050920 Mozilla/5.0 (X11; U; Linux i686; en-us; rv:1.9.0.2) Gecko/2008092313 Ubuntu/9.04 (jaunty) Firefox/3.5 OpenCalaisSemanticProxy PycURL/7.18.2 PycURL/7.19.3 Python-urllib/1.17 Twingly Recon twitmatic Twitturly / v0.6 Wget/1.10.2 (Red Hat modified) Wget/1.11.1 (Red Hat modified) Of the few user-agents that seem ‘real’ at first, half are originating from an ip-address used by Amazon EC2. And I doubt people are setting op proxies on there. Oh yeah, Googlebot (the real deal, from a legit google owned address) is sucking up posted links like fresh oysters. I guess google is trying to make sure in advance to never be beaten by twitter in the ‘realtime search’ department. Actually, I think it’d be almost stupid NOT to post any new pages/posts/websites on Twitter, it must be one of the fastest ways to get a Googlebot visit. Same experiment with a real, established twitter account Now, because I was posting the url’s either as ’status’ messages or directed @people, on a test-account with hardly any (human) followers, I checked again using the twitter accounts from a commercial site I’m involved with. These accounts all have between 500 and 1000 targeted (I think) followers. I checked the destination access_logs and also added ‘my’ redirect after the bit.ly redirect: same results, although seemingly a bit higher real visitor/bot ratio. Btw: one of these account was ‘punished’ with a 1 week lock recently because the same (1 one!) status update was sent that was sent right before using another account. They got an email explaining the lock because the account didn’t act according to their TOS. I can’t find anything in their TOS about it, can you? I don’t think Twitter is on the right track punishing a legit account, knowing the trickery I had been doing with it’s api went totally unpunished. I might be wrong though, I often am. On the other hand: this commercial site reported targeted traffic and actual signups from visitors coming from Twitter. The ones that are really real visitors are also very targeted. I’m just not sure if the amount of work involved could hold up against an adwords campaign. Reposting the same link over and over again helps On thing I noticed: It helps to keep on reposting the same links with regular intervals. I guess most people only look at their first page when checking out recent posts of the ones they’re following, or don’t look too far back when performing a search. Now, this probably isn’t according to the twitter TOS. Actually, it might be spamming but no-one is obligated to follow anyone else of course. This way, I was getting more real visitors and less bots. To my surprise (when my programmer’s hat is on) there were still repeated visits from the same bots coming from the same ip-addresses. Did they expect to find something else when visiting for a 2nd or 3rd time? (actually,this gave me an idea: you can’t change a link once it’s posted, but you can change where it redirects to) Most bots were smart enough not to follow the same link again though. Are you successful in getting real visitors from Twitter? Are you only relying on bit.ly to provide traffic stats?

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Launching a WPF Window in a Separate Thread, Part 1

- by Reed

Typically, I strongly recommend keeping the user interface within an application’s main thread, and using multiple threads to move the actual “work” into background threads. However, there are rare times when creating a separate, dedicated thread for a Window can be beneficial. This is even acknowledged in the MSDN samples, such as the Multiple Windows, Multiple Threads sample. However, doing this correctly is difficult. Even the referenced MSDN sample has major flaws, and will fail horribly in certain scenarios. To ease this, I wrote a small class that alleviates some of the difficulties involved. The MSDN Multiple Windows, Multiple Threads Sample shows how to launch a new thread with a WPF Window, and will work in most cases. The sample code (commented and slightly modified) works out to the following: // Create a thread Thread newWindowThread = new Thread(new ThreadStart( () => { // Create and show the Window Window1 tempWindow = new Window1(); tempWindow.Show(); // Start the Dispatcher Processing System.Windows.Threading.Dispatcher.Run(); })); // Set the apartment state newWindowThread.SetApartmentState(ApartmentState.STA); // Make the thread a background thread newWindowThread.IsBackground = true; // Start the thread newWindowThread.Start(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This sample creates a thread, marks it as single threaded apartment state, and starts the Dispatcher on that thread. That is the minimum requirements to get a Window displaying and handling messages correctly, but, unfortunately, has some serious flaws. The first issue – the created thread will run continuously until the application shuts down, given the code in the sample. The problem is that the ThreadStart delegate used ends with running the Dispatcher. However, nothing ever stops the Dispatcher processing. The thread was created as a Background thread, which prevents it from keeping the application alive, but the Dispatcher will continue to pump dispatcher frames until the application shuts down. In order to fix this, we need to call Dispatcher.InvokeShutdown after the Window is closed. This would require modifying the above sample to subscribe to the Window’s Closed event, and, at that point, shutdown the Dispatcher: // Create a thread Thread newWindowThread = new Thread(new ThreadStart( () => { Window1 tempWindow = new Window1(); // When the window closes, shut down the dispatcher tempWindow.Closed += (s,e) => Dispatcher.CurrentDispatcher.BeginInvokeShutdown(DispatcherPriority.Background); tempWindow.Show(); // Start the Dispatcher Processing System.Windows.Threading.Dispatcher.Run(); })); // Setup and start thread as before This eliminates the first issue. Now, when the Window is closed, the new thread’s Dispatcher will shut itself down, which in turn will cause the thread to complete. The above code will work correctly for most situations. However, there is still a potential problem which could arise depending on the content of the Window1 class. This is particularly nasty, as the code could easily work for most windows, but fail on others. The problem is, at the point where the Window is constructed, there is no active SynchronizationContext. This is unlikely to be a problem in most cases, but is an absolute requirement if there is code within the constructor of Window1 which relies on a context being in place. While this sounds like an edge case, it’s fairly common. For example, if a BackgroundWorker is started within the constructor, or a TaskScheduler is built using TaskScheduler.FromCurrentSynchronizationContext() with the expectation of synchronizing work to the UI thread, an exception will be raised at some point. Both of these classes rely on the existence of a proper context being installed to SynchronizationContext.Current, which happens automatically, but not until Dispatcher.Run is called. In the above case, SynchronizationContext.Current will return null during the Window’s construction, which can cause exceptions to occur or unexpected behavior. Luckily, this is fairly easy to correct. We need to do three things, in order, prior to creating our Window: Create and initialize the Dispatcher for the new thread manually Create a synchronization context for the thread which uses the Dispatcher Install the synchronization context Creating the Dispatcher is quite simple – The Dispatcher.CurrentDispatcher property gets the current thread’s Dispatcher and “creates a new Dispatcher if one is not already associated with the thread.” Once we have the correct Dispatcher, we can create a SynchronizationContext which uses the dispatcher by creating a DispatcherSynchronizationContext. Finally, this synchronization context can be installed as the current thread’s context via SynchronizationContext.SetSynchronizationContext. These three steps can easily be added to the above via a single line of code: // Create a thread Thread newWindowThread = new Thread(new ThreadStart( () => { // Create our context, and install it: SynchronizationContext.SetSynchronizationContext( new DispatcherSynchronizationContext( Dispatcher.CurrentDispatcher)); Window1 tempWindow = new Window1(); // When the window closes, shut down the dispatcher tempWindow.Closed += (s,e) => Dispatcher.CurrentDispatcher.BeginInvokeShutdown(DispatcherPriority.Background); tempWindow.Show(); // Start the Dispatcher Processing System.Windows.Threading.Dispatcher.Run(); })); // Setup and start thread as before This now forces the synchronization context to be in place before the Window is created and correctly shuts down the Dispatcher when the window closes. However, there are quite a few steps. In my next post, I’ll show how to make this operation more reusable by creating a class with a far simpler API…

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Creating and maintaining Orchard translations

- by Bertrand Le Roy

Many volunteers have already stepped up to provide translations for Orchard. There are many challenges to overcome with translating such a project. Orchard is a very modular CMS, so the translation mechanism needs to account for the core as well as first and third party modules and themes. Another issue is that every new version of Orchard or of a module changes some localizable strings and adds new ones as others enter obsolescence. In order to address those problems, I've built a small Orchard module that automates some of the most complex tasks that maintaining a translation implies. In this post, I'll walk you through the operations I had to do to update the French translation for Orchard 1.0. In order to make sure you translate all the first party modules, I would recommend that you start from a full source code enlistment. The reason is that I'll show how you can extract the default en-US translation from any source code enlistment. That enables you to create a translation that is even more up-to-date than what is currently on the site. Alternatively, you could start by downloading the current en-US translation. If you decide to do so, just skip the relevant paragraphs. First, let's install the Orchard Translation Manager. I'm starting from a vanilla clone of the latest in the code repository. After you've setup the site, go into the dashboard and click on Gallery. Locate the Orchard Translation Manager in the list of modules and click "Install". Once the module is installed, you need to enable its one feature by going into Configuration/Features and clicking "Enable" next to Vandelay.TranslationManager. We're done with the setup that we need in order to start our translation work. We'll now switch to the command-line and to our favorite text editor. Open a command-line on the Orchard web site folder. I found the easiest way to do this is to do a SHIFT+right-click on the Orchard.Web folder in Windows Explorer and to click "Open command window here". Type bin\orchard to enter the Orchard command-line environment. If you do a "help commands" you should see four commands in the list that came from the module we just installed: extract default translation, install translation, package translation and sync translation. First, we're going to generate the default translation. Note that it is possible to generate that default translation for a specific list of modules and themes by using the /Extensions: switch, which should facilitate the translation of third party extensions, but in this tutorial we're going to generate it for the whole of the Orchard source code. extract default translation /Output:\temp .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This should have created an Orchard.en-us.po.zip file in the temp directory. Extract that archive into an orchard.po folder under \temp. The next step depends on whether you have an existing translation that you want to update or not. If you do have an existing translation, just extract it into the same \temp\orchard.po directory. That should result in a file structure where you have the default en-US translation alongside your own. If you don't have an existing translation, just continue, the commands will be the same. We are now going to synchronize those translations (or generate the stub for a new one if you didn't start from an existing translation). sync translation /Input:\temp\orchard.po /Culture:fr-FR After this command (where you should of course substitute fr-FR with the culture you're working on), we now have updated files that contain a few useful flags. Open each of the .po files under the culture you are working on (there should be around 36) with your favorite text editor. For all the strings that are still valid in the latest version, nothing changes and you don't need to do anything. For all the strings that disappeared from the default culture, the old translation will still be there but they will be prefixed with the following comment: # Obsolete translation Conveniently, all the obsolete strings will be grouped at the end of the file. You can select all those and delete them. For all the new strings, you will see the following comment: # Untranslated string This is where the hard work begins. You'll need to translate each of those new strings by entering the translation between the quotes in: msgstr "" Don't introduce hard carriage returns in the strings, just stay on one line (your text editor should do some reasonable wrapping so this shouldn't be a big deal). Once you're done with a file, save it. Make sure, and this is very important, that your text editor is saving using the UTF-8 encoding. In Notepad, that setting can be found in the file saving dialog by doing a "Save As" rather than a plain "Save": When all the po files have been edited, you are ready to package the translation for submission (a.k.a. sending e-mail to the localization mailing list). package translation /Culture:fr-FR /Input:\temp\orchard.po /Output:\temp You should now see a Orchard.fr-FR.po.zip file in temp that is ready to be submitted. That is, once you've tested it, which can be done by deploying it into the site: install translation \temp\orchard.fr-fr.po.zip Once this is done you can go into the dashboard under Configuration/Settings and click on "Add or remove supported cultures for the site". Choose your culture and click "Add". You can go back to settings and set the default culture. Save. You may now take a tour of the application and verify that everything works as expected: And that's it really. Creating a translation for Orchard is a matter of a few hours. If you don't see a translation for your culture, please consider creating it.

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New Features in ASP.NET Web API 2 - Part I

- by dwahlin

I’m a big fan of ASP.NET Web API. It provides a quick yet powerful way to build RESTful HTTP services that can easily be consumed by a variety of clients. While it’s simple to get started using, it has a wealth of features such as filters, formatters, and message handlers that can be used to extend it when needed. In this post I’m going to provide a quick walk-through of some of the key new features in version 2. I’ll focus on some two of my favorite features that are related to routing and HTTP responses and cover additional features in a future post. Attribute Routing Routing has been a core feature of Web API since it’s initial release and something that’s built into new Web API projects out-of-the-box. However, there are a few scenarios where defining routes can be challenging such as nested routes (more on that in a moment) and any situation where a lot of custom routes have to be defined. For this example, let’s assume that you’d like to define the following nested route: /customers/1/orders This type of route would select a customer with an Id of 1 and then return all of their orders. Defining this type of route in the standard WebApiConfig class is certainly possible, but it isn’t the easiest thing to do for people who don’t understand routing well. Here’s an example of how the route shown above could be defined: public static class WebApiConfig { public static void Register(HttpConfiguration config) { config.Routes.MapHttpRoute( name: "CustomerOrdersApiGet", routeTemplate: "api/customers/{custID}/orders", defaults: new { custID = 0, controller = "Customers", action = "Orders" } ); config.Routes.MapHttpRoute( name: "DefaultApi", routeTemplate: "api/{controller}/{id}", defaults: new { id = RouteParameter.Optional } ); GlobalConfiguration.Configuration.Formatters.Insert(0, new JsonpFormatter()); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } With attribute based routing, defining these types of nested routes is greatly simplified. To get started you first need to make a call to the new MapHttpAttributeRoutes() method in the standard WebApiConfig class (or a custom class that you may have created that defines your routes) as shown next: public static class WebApiConfig { public static void Register(HttpConfiguration config) { // Allow for attribute based routes config.MapHttpAttributeRoutes(); config.Routes.MapHttpRoute( name: "DefaultApi", routeTemplate: "api/{controller}/{id}", defaults: new { id = RouteParameter.Optional } ); } } Once attribute based routes are configured, you can apply the Route attribute to one or more controller actions. Here’s an example: [HttpGet] [Route("customers/{custId:int}/orders")] public List<Order> Orders(int custId) { var orders = _Repository.GetOrders(custId); if (orders == null) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound)); } return orders; } This example maps the custId route parameter to the custId parameter in the Orders() method and also ensures that the route parameter is typed as an integer. The Orders() method can be called using the following route: /customers/2/orders While this is extremely easy to use and gets the job done, it doesn’t include the default “api” string on the front of the route that you might be used to seeing. You could add “api” in front of the route and make it “api/customers/{custId:int}/orders” but then you’d have to repeat that across other attribute-based routes as well. To simply this type of task you can add the RoutePrefix attribute above the controller class as shown next so that “api” (or whatever the custom starting point of your route is) is applied to all attribute routes: [RoutePrefix("api")] public class CustomersController : ApiController { [HttpGet] [Route("customers/{custId:int}/orders")] public List<Order> Orders(int custId) { var orders = _Repository.GetOrders(custId); if (orders == null) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound)); } return orders; } } There’s much more that you can do with attribute-based routing in ASP.NET. Check out the following post by Mike Wasson for more details. Returning Responses with IHttpActionResult The first version of Web API provided a way to return custom HttpResponseMessage objects which were pretty easy to use overall. However, Web API 2 now wraps some of the functionality available in version 1 to simplify the process even more. A new interface named IHttpActionResult (similar to ActionResult in ASP.NET MVC) has been introduced which can be used as the return type for Web API controller actions. To return a custom response you can use new helper methods exposed through ApiController such as: Ok NotFound Exception Unauthorized BadRequest Conflict Redirect InvalidModelState Here’s an example of how IHttpActionResult and the helper methods can be used to cleanup code. This is the typical way to return a custom HTTP response in version 1: public HttpResponseMessage Delete(int id) { var status = _Repository.DeleteCustomer(id); if (status) { return new HttpResponseMessage(HttpStatusCode.OK); } else { throw new HttpResponseException(HttpStatusCode.NotFound); } } With version 2 we can replace HttpResponseMessage with IHttpActionResult and simplify the code quite a bit: public IHttpActionResult Delete(int id) { var status = _Repository.DeleteCustomer(id); if (status) { //return new HttpResponseMessage(HttpStatusCode.OK); return Ok(); } else { //throw new HttpResponseException(HttpStatusCode.NotFound); return NotFound(); } } You can also cleanup post (insert) operations as well using the helper methods. Here’s a version 1 post action: public HttpResponseMessage Post([FromBody]Customer cust) { var newCust = _Repository.InsertCustomer(cust); if (newCust != null) { var msg = new HttpResponseMessage(HttpStatusCode.Created); msg.Headers.Location = new Uri(Request.RequestUri + newCust.ID.ToString()); return msg; } else { throw new HttpResponseException(HttpStatusCode.Conflict); } } This is what the code looks like in version 2: public IHttpActionResult Post([FromBody]Customer cust) { var newCust = _Repository.InsertCustomer(cust); if (newCust != null) { return Created<Customer>(Request.RequestUri + newCust.ID.ToString(), newCust); } else { return Conflict(); } } More details on IHttpActionResult and the different helper methods provided by the ApiController base class can be found here. Conclusion Although there are several additional features available in Web API 2 that I could cover (CORS support for example), this post focused on two of my favorites features. If you have .NET 4.5.1 available then I definitely recommend checking the new features out. Additional articles that cover features in ASP.NET Web API 2 can be found here.

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Adding RSS to tags in Orchard

- by Bertrand Le Roy

A year ago, I wrote a scary post about RSS in Orchard. RSS was one of the first features we implemented in our CMS, and it has stood the test of time rather well, but the post was explaining things at a level that was probably too abstract whereas my readers were expecting something a little more practical. Well, this post is going to correct this by showing how I built a module that adds RSS feeds for each tag on the site. Hopefully it will show that it's not very complicated in practice, and also that the infrastructure is pretty well thought out. In order to provide RSS, we need to do two things: generate the XML for the feed, and inject the address of that feed into the existing tag listing page, in order to make the feed discoverable. Let's start with the discoverability part. One might be tempted to replace the controller or the view that are responsible for the listing of the items under a tag. Fortunately, there is no need to do any of that, and we can be a lot less obtrusive. Instead, we can implement a filter: public class TagRssFilter : FilterProvider, IResultFilter .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } On this filter, we can implement the OnResultExecuting method and simply check whether the current request is targeting the list of items under a tag. If that is the case, we can just register our new feed: public void OnResultExecuting(ResultExecutingContext filterContext) { var routeValues = filterContext.RouteData.Values; if (routeValues["area"] as string == "Orchard.Tags" && routeValues["controller"] as string == "Home" && routeValues["action"] as string == "Search") { var tag = routeValues["tagName"] as string; if (! string.IsNullOrWhiteSpace(tag)) { var workContext = _wca.GetContext(); _feedManager.Register( workContext.CurrentSite + " – " + tag, "rss", new RouteValueDictionary { { "tag", tag } } ); } } } The registration of the new feed is just specifying the title of the feed, its format (RSS) and the parameters that it will need (the tag). _wca and _feedManager are just instances of IWorkContextAccessor and IFeedManager that Orchard injected for us. That is all that's needed to get the following tag to be added to the head of our page, without touching an existing controller or view: <link rel="alternate" type="application/rss+xml" title="VuLu - Science" href="/rss?tag=Science"/> Nifty. Of course, if we navigate to the URL of that feed, we'll get a 404. This is because no implementation of IFeedQueryProvider knows about the tag parameter yet. Let's build one that does: public class TagFeedQuery : IFeedQueryProvider, IFeedQuery IFeedQueryProvider has one method, Match, that we can implement to take over any feed request that has a tag parameter: public FeedQueryMatch Match(FeedContext context) { var tagName = context.ValueProvider.GetValue("tag"); if (tagName == null) return null; return new FeedQueryMatch { FeedQuery = this, Priority = -5 }; } This is just saying that if there is a tag parameter, we will handle it. All that remains to be done is the actual building of the feed now that we have accepted to handle it. This is done by implementing the Execute method of the IFeedQuery interface: public void Execute(FeedContext context) { var tagValue = context.ValueProvider.GetValue("tag"); if (tagValue == null) return; var tagName = (string)tagValue.ConvertTo(typeof (string)); var tag = _tagService.GetTagByName(tagName); if (tag == null) return; var site = _services.WorkContext.CurrentSite; var link = new XElement("link"); context.Response.Element.SetElementValue("title", site.SiteName + " - " + tagName); context.Response.Element.Add(link); context.Response.Element.SetElementValue("description", site.SiteName + " - " + tagName); context.Response.Contextualize(requestContext => link.Add(GetTagUrl(tagName, requestContext))); var items = _tagService.GetTaggedContentItems(tag.Id, 0, 20); foreach (var item in items) { context.Builder.AddItem(context, item.ContentItem); } } This code is resolving the tag content item from its name and then gets content items tagged with it, using the tag services provided by the Orchard.Tags module. Then we add those items to the feed. And that is it. To summarize, we handled the request unobtrusively in order to inject the feed's link, then handled requests for feeds with a tag parameter and generated the list of items for that tag. It remains fairly simple and still it is able to handle arbitrary content types. That makes me quite happy about our little piece of over-engineered code from last year. The full code for this can be found in the Vandelay.TagCloud module: http://orchardproject.net/gallery/List/Modules/ Orchard.Module.Vandelay.TagCloud/1.2

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Creating a podcast feed for iTunes & BlackBerry users using WCF Syndication

- by brian_ritchie

In my previous post, I showed how to create a RSS feed using WCF Syndication. Next, I'll show how to add the additional tags needed to turn a RSS feed into an iTunes podcast. A podcast is merely a RSS feed with some special characteristics: iTunes RSS tags. These are additional tags beyond the standard RSS spec. Apple has a good page on the requirements. Audio file enclosure. This is a link to the audio file (such as mp3) hosted by your site. Apple doesn't host the audio, they just read the meta-data from the RSS feed into their system. The SyndicationFeed class supports both AttributeExtensions & ElementExtensions to add custom tags to the RSS feeds. A couple of points of interest in the code below: The imageUrl below provides the album cover for iTunes (170px × 170px) Each SyndicationItem corresponds to an audio episode in your podcast So, here's the code: .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: Consolas, "Courier New", Courier, Monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } 1: XNamespace itunesNS = "http://www.itunes.com/dtds/podcast-1.0.dtd"; 2: string prefix = "itunes"; 3: 4: var feed = new SyndicationFeed(title, description, new Uri(link)); 5: feed.Categories.Add(new SyndicationCategory(category)); 6: feed.AttributeExtensions.Add(new XmlQualifiedName(prefix, 7: "http://www.w3.org/2000/xmlns/"), itunesNS.NamespaceName); 8: feed.Copyright = new TextSyndicationContent(copyright); 9: feed.Language = "en-us"; 10: feed.Copyright = new TextSyndicationContent(DateTime.Now.Year + " " + ownerName); 11: feed.ImageUrl = new Uri(imageUrl); 12: feed.LastUpdatedTime = DateTime.Now; 13: feed.Authors.Add(new SyndicationPerson() {Name=ownerName, Email=ownerEmail }); 14: var extensions = feed.ElementExtensions; 15: extensions.Add(new XElement(itunesNS + "subtitle", subTitle).CreateReader()); 16: extensions.Add(new XElement(itunesNS + "image", 17: new XAttribute("href", imageUrl)).CreateReader()); 18: extensions.Add(new XElement(itunesNS + "author", ownerName).CreateReader()); 19: extensions.Add(new XElement(itunesNS + "summary", description).CreateReader()); 20: extensions.Add(new XElement(itunesNS + "category", 21: new XAttribute("text", category), 22: new XElement(itunesNS + "category", 23: new XAttribute("text", subCategory))).CreateReader()); 24: extensions.Add(new XElement(itunesNS + "explicit", "no").CreateReader()); 25: extensions.Add(new XDocument( 26: new XElement(itunesNS + "owner", 27: new XElement(itunesNS + "name", ownerName), 28: new XElement(itunesNS + "email", ownerEmail))).CreateReader()); 29: 30: var feedItems = new List<SyndicationItem>(); 31: foreach (var i in Items) 32: { 33: var item = new SyndicationItem(i.title, null, new Uri(link)); 34: item.Summary = new TextSyndicationContent(i.summary); 35: item.Id = i.id; 36: if (i.publishedDate != null) 37: item.PublishDate = (DateTimeOffset)i.publishedDate; 38: item.Links.Add(new SyndicationLink() { 39: Title = i.title, Uri = new Uri(link), 40: Length = i.size, MediaType = i.mediaType }); 41: var itemExt = item.ElementExtensions; 42: itemExt.Add(new XElement(itunesNS + "subtitle", i.subTitle).CreateReader()); 43: itemExt.Add(new XElement(itunesNS + "summary", i.summary).CreateReader()); 44: itemExt.Add(new XElement(itunesNS + "duration", 45: string.Format("{0}:{1:00}:{2:00}", 46: i.duration.Hours, i.duration.Minutes, i.duration.Seconds) 47: ).CreateReader()); 48: itemExt.Add(new XElement(itunesNS + "keywords", i.keywords).CreateReader()); 49: itemExt.Add(new XElement(itunesNS + "explicit", "no").CreateReader()); 50: itemExt.Add(new XElement("enclosure", new XAttribute("url", i.url), 51: new XAttribute("length", i.size), new XAttribute("type", i.mediaType))); 52: feedItems.Add(item); 53: } 54: 55: feed.Items = feedItems; If you're hosting your podcast feed within a MVC project, you can use the code from my previous post to stream it. Once you have created your feed, you can use the Feed Validator tool to make sure it is up to spec. Or you can use iTunes: Launch iTunes. In the Advanced menu, select Subscribe to Podcast. Enter your feed URL in the text box and click OK. After you've verified your feed is solid & good to go, you can submit it to iTunes. Launch iTunes. In the left navigation column, click on iTunes Store to open the store. Once the store loads, click on Podcasts along the top navigation bar to go to the Podcasts page. In the right column of the Podcasts page, click on the Submit a Podcast link. Follow the instructions on the Submit a Podcast page. Here are the full instructions. Once they have approved your podcast, it will be available within iTunes. RIM has also gotten into the podcasting business...which is great for BlackBerry users. They accept the same enhanced-RSS feed that iTunes uses, so just create an account with them & submit the feed's URL. It goes through a similar approval process to iTunes. BlackBerry users must be on BlackBerry 6 OS or download the Podcast App from App World. In my next post, I'll show how to build the podcast feed dynamically from the ID3 tags within the MP3 files.

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Changing CSS with jQuery syntax in Silverlight using jLight

- by Timmy Kokke

Lately I’ve ran into situations where I had to change elements or had to request a value in the DOM from Silverlight. jLight, which was introduced in an earlier article, can help with that. jQuery offers great ways to change CSS during runtime. Silverlight can access the DOM, but it isn’t as easy as jQuery. All examples shown in this article can be looked at in this online demo. The code can be downloaded here. Part 1: The easy stuff Selecting and changing properties is pretty straight forward. Setting the text color in all <B> </B> elements can be done using the following code: jQuery.Select("b").Css("color", "red"); The Css() method is an extension method on jQueryObject which is return by the jQuery.Select() method. The Css() method takes to parameters. The first is the Css style property. All properties used in Css can be entered in this string. The second parameter is the value you want to give the property. In this case the property is “color” and it is changed to “red”. To specify which element you want to select you can add a :selector parameter to the Select() method as shown in the next example. jQuery.Select("b:first").Css("font-family", "sans-serif"); The “:first” pseudo-class selector selects only the first element. This example changes the “font-family” property of the first <B></B> element to “sans-serif”. To make use of intellisense in Visual Studio I’ve added a extension methods to help with the pseudo-classes. In the example below the “font-weight” of every “Even” <LI></LI> is set to “bold”. jQuery.Select("li".Even()).Css("font-weight", "bold"); Because the Css() extension method returns a jQueryObject it is possible to chain calls to Css(). The following example show setting the “color”, “background-color” and the “font-size” of all headers in one go. jQuery.Select(":header").Css("color", "#12FF70") .Css("background-color", "yellow") .Css("font-size", "25px"); Part 2: More complex stuff In only a few cases you need to change only one style property. More often you want to change an entire set op style properties all in one go. You could chain a lot of Css() methods together. A better way is to add a class to a stylesheet and define all properties in there. With the AddClass() method you can set a style class to a set of elements. This example shows how to add the “demostyle” class to all <B></B> in the document. jQuery.Select("b").AddClass("demostyle"); Removing the class works in the same way: jQuery.Select("b").RemoveClass("demostyle"); jLight is build for interacting with to the DOM from Silverlight using jQuery. A jQueryObjectCss object can be used to define different sets of style properties in Silverlight. The over 60 most common Css style properties are defined in the jQueryObjectCss class. A string indexer can be used to access all style properties ( CssObject1[“background-color”] equals CssObject1.BackgroundColor). In the code below, two jQueryObjectCss objects are defined and instantiated. private jQueryObjectCss CssObject1; private jQueryObjectCss CssObject2; public Demo2() { CssObject1 = new jQueryObjectCss { BackgroundColor = "Lime", Color="Black", FontSize = "12pt", FontFamily = "sans-serif", FontWeight = "bold", MarginLeft = 150, LineHeight = "28px", Border = "Solid 1px #880000" }; CssObject2 = new jQueryObjectCss { FontStyle = "Italic", FontSize = "48", Color = "#225522" }; InitializeComponent(); } Now instead of chaining to set all different properties you can just pass one of the jQueryObjectCss objects to the Css() method. In this case all <LI></LI> elements are set to match this object. jQuery.Select("li").Css(CssObject1); When using the jQueryObjectCss objects chaining is still possible. In the following example all headers are given a blue backgroundcolor and the last is set to match CssObject2. jQuery.Select(":header").Css(new jQueryObjectCss{BackgroundColor = "Blue"}) .Eq(-1).Css(CssObject2); Part 3: The fun stuff Having Silverlight call JavaScript and than having JavaScript to call Silverlight requires a lot of plumbing code. Everything has to be registered and strings are passed back and forth to execute the JavaScript. jLight makes this kind of stuff so easy, it becomes fun to use. In a lot of situations jQuery can call a function to decide what to do, setting a style class based on complex expressions for example. jLight can do the same, but the callback methods are defined in Silverlight. This example calls the function() method for each <LI></LI> element. The callback method has to take a jQueryObject, an integer and a string as parameters. In this case jLight differs a bit from the actual jQuery implementation. jQuery uses only the index and the className parameters. A jQueryObject is added to make it simpler to access the attributes and properties of the element. If the text of the listitem starts with a ‘D’ or an ‘M’ the class is set. Otherwise null is returned and nothing happens. private void button1_Click(object sender, RoutedEventArgs e) { jQuery.Select("li").AddClass(function); } private string function(jQueryObject obj, int index, string className) { if (obj.Text[0] == 'D' || obj.Text[0] == 'M') return "demostyle"; return null; } The last thing I would like to demonstrate uses even more Silverlight and less jLight, but demonstrates the power of the combination. Animating a style property using a Storyboard with easing functions. First a dependency property is defined. In this case it is a double named Intensity. By handling the changed event the color is set using jQuery. public double Intensity { get { return (double)GetValue(IntensityProperty); } set { SetValue(IntensityProperty, value); } } public static readonly DependencyProperty IntensityProperty = DependencyProperty.Register("Intensity", typeof(double), typeof(Demo3), new PropertyMetadata(0.0, IntensityChanged)); private static void IntensityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var i = (byte)(double)e.NewValue; jQuery.Select("span").Css("color", string.Format("#{0:X2}{0:X2}{0:X2}", i)); } An animation has to be created. This code defines a Storyboard with one keyframe that uses a bounce ease as an easing function. The animation is set to target the Intensity dependency property defined earlier. private Storyboard CreateAnimation(double value) { Storyboard storyboard = new Storyboard(); var da = new DoubleAnimationUsingKeyFrames(); var d = new EasingDoubleKeyFrame { EasingFunction = new BounceEase(), KeyTime = KeyTime.FromTimeSpan(TimeSpan.FromSeconds(1.0)), Value = value }; da.KeyFrames.Add(d); Storyboard.SetTarget(da, this); Storyboard.SetTargetProperty(da, new PropertyPath(Demo3.IntensityProperty)); storyboard.Children.Add(da); return storyboard; } Initially the Intensity is set to 128 which results in a gray color. When one of the buttons is pressed, a new animation is created an played. One to animate to black, and one to animate to white. public Demo3() { InitializeComponent(); Intensity = 128; } private void button2_Click(object sender, RoutedEventArgs e) { CreateAnimation(255).Begin(); } private void button3_Click(object sender, RoutedEventArgs e) { CreateAnimation(0).Begin(); } Conclusion As you can see jLight can make the life of a Silverlight developer a lot easier when accessing the DOM. Almost all jQuery functions that are defined in jLight use the same constructions as described above. I’ve tried to stay as close as possible to the real jQuery. Having JavaScript perform callbacks to Silverlight using jLight will be described in more detail in a future tutorial about AJAX or eventing.

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C# Performance Pitfall – Interop Scenarios Change the Rules

- by Reed

C# and .NET, overall, really do have fantastic performance in my opinion. That being said, the performance characteristics dramatically differ from native programming, and take some relearning if you’re used to doing performance optimization in most other languages, especially C, C++, and similar. However, there are times when revisiting tricks learned in native code play a critical role in performance optimization in C#. I recently ran across a nasty scenario that illustrated to me how dangerous following any fixed rules for optimization can be… The rules in C# when optimizing code are very different than C or C++. Often, they’re exactly backwards. For example, in C and C++, lifting a variable out of loops in order to avoid memory allocations often can have huge advantages. If some function within a call graph is allocating memory dynamically, and that gets called in a loop, it can dramatically slow down a routine. This can be a tricky bottleneck to track down, even with a profiler. Looking at the memory allocation graph is usually the key for spotting this routine, as it’s often “hidden” deep in call graph. For example, while optimizing some of my scientific routines, I ran into a situation where I had a loop similar to: for (i=0; i<numberToProcess; ++i) { // Do some work ProcessElement(element[i]); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This loop was at a fairly high level in the call graph, and often could take many hours to complete, depending on the input data. As such, any performance optimization we could achieve would be greatly appreciated by our users. After a fair bit of profiling, I noticed that a couple of function calls down the call graph (inside of ProcessElement), there was some code that effectively was doing: // Allocate some data required DataStructure* data = new DataStructure(num); // Call into a subroutine that passed around and manipulated this data highly CallSubroutine(data); // Read and use some values from here double values = data->Foo; // Cleanup delete data; // ... return bar; Normally, if “DataStructure” was a simple data type, I could just allocate it on the stack. However, it’s constructor, internally, allocated it’s own memory using new, so this wouldn’t eliminate the problem. In this case, however, I could change the call signatures to allow the pointer to the data structure to be passed into ProcessElement and through the call graph, allowing the inner routine to reuse the same “data” memory instead of allocating. At the highest level, my code effectively changed to something like: DataStructure* data = new DataStructure(numberToProcess); for (i=0; i<numberToProcess; ++i) { // Do some work ProcessElement(element[i], data); } delete data; Granted, this dramatically reduced the maintainability of the code, so it wasn’t something I wanted to do unless there was a significant benefit. In this case, after profiling the new version, I found that it increased the overall performance dramatically – my main test case went from 35 minutes runtime down to 21 minutes. This was such a significant improvement, I felt it was worth the reduction in maintainability. In C and C++, it’s generally a good idea (for performance) to: Reduce the number of memory allocations as much as possible, Use fewer, larger memory allocations instead of many smaller ones, and Allocate as high up the call stack as possible, and reuse memory I’ve seen many people try to make similar optimizations in C# code. For good or bad, this is typically not a good idea. The garbage collector in .NET completely changes the rules here. In C#, reallocating memory in a loop is not always a bad idea. In this scenario, for example, I may have been much better off leaving the original code alone. The reason for this is the garbage collector. The GC in .NET is incredibly effective, and leaving the allocation deep inside the call stack has some huge advantages. First and foremost, it tends to make the code more maintainable – passing around object references tends to couple the methods together more than necessary, and overall increase the complexity of the code. This is something that should be avoided unless there is a significant reason. Second, (unlike C and C++) memory allocation of a single object in C# is normally cheap and fast. Finally, and most critically, there is a large advantage to having short lived objects. If you lift a variable out of the loop and reuse the memory, its much more likely that object will get promoted to Gen1 (or worse, Gen2). This can cause expensive compaction operations to be required, and also lead to (at least temporary) memory fragmentation as well as more costly collections later. As such, I’ve found that it’s often (though not always) faster to leave memory allocations where you’d naturally place them – deep inside of the call graph, inside of the loops. This causes the objects to stay very short lived, which in turn increases the efficiency of the garbage collector, and can dramatically improve the overall performance of the routine as a whole. In C#, I tend to: Keep variable declarations in the tightest scope possible Declare and allocate objects at usage While this tends to cause some of the same goals (reducing unnecessary allocations, etc), the goal here is a bit different – it’s about keeping the objects rooted for as little time as possible in order to (attempt) to keep them completely in Gen0, or worst case, Gen1. It also has the huge advantage of keeping the code very maintainable – objects are used and “released” as soon as possible, which keeps the code very clean. It does, however, often have the side effect of causing more allocations to occur, but keeping the objects rooted for a much shorter time. Now – nowhere here am I suggesting that these rules are hard, fast rules that are always true. That being said, my time spent optimizing over the years encourages me to naturally write code that follows the above guidelines, then profile and adjust as necessary. In my current project, however, I ran across one of those nasty little pitfalls that’s something to keep in mind – interop changes the rules. In this case, I was dealing with an API that, internally, used some COM objects. In this case, these COM objects were leading to native allocations (most likely C++) occurring in a loop deep in my call graph. Even though I was writing nice, clean managed code, the normal managed code rules for performance no longer apply. After profiling to find the bottleneck in my code, I realized that my inner loop, a innocuous looking block of C# code, was effectively causing a set of native memory allocations in every iteration. This required going back to a “native programming” mindset for optimization. Lifting these variables and reusing them took a 1:10 routine down to 0:20 – again, a very worthwhile improvement. Overall, the lessons here are: Always profile if you suspect a performance problem – don’t assume any rule is correct, or any code is efficient just because it looks like it should be Remember to check memory allocations when profiling, not just CPU cycles Interop scenarios often cause managed code to act very differently than “normal” managed code. Native code can be hidden very cleverly inside of managed wrappers

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Setting useLegacyV2RuntimeActivationPolicy At Runtime

- by Reed

Version 4.0 of the .NET Framework included a new CLR which is almost entirely backwards compatible with the 2.0 version of the CLR. However, by default, mixed-mode assemblies targeting .NET 3.5sp1 and earlier will fail to load in a .NET 4 application. Fixing this requires setting useLegacyV2RuntimeActivationPolicy in your app.Config for the application. While there are many good reasons for this decision, there are times when this is extremely frustrating, especially when writing a library. As such, there are (rare) times when it would be beneficial to set this in code, at runtime, as well as verify that it’s running correctly prior to receiving a FileLoadException. Typically, loading a pre-.NET 4 mixed mode assembly is handled simply by changing your app.Config file, and including the relevant attribute in the startup element: <?xml version="1.0" encoding="utf-8" ?> <configuration> <startup useLegacyV2RuntimeActivationPolicy="true"> <supportedRuntime version="v4.0"/> </startup> </configuration> .csharpcode { background-color: #ffffff; font-family: consolas, "Courier New", courier, monospace; color: black; font-size: small } .csharpcode pre { background-color: #ffffff; font-family: consolas, "Courier New", courier, monospace; color: black; font-size: small } .csharpcode pre { margin: 0em } .csharpcode .rem { color: #008000 } .csharpcode .kwrd { color: #0000ff } .csharpcode .str { color: #006080 } .csharpcode .op { color: #0000c0 } .csharpcode .preproc { color: #cc6633 } .csharpcode .asp { background-color: #ffff00 } .csharpcode .html { color: #800000 } .csharpcode .attr { color: #ff0000 } .csharpcode .alt { background-color: #f4f4f4; margin: 0em; width: 100% } .csharpcode .lnum { color: #606060 } This causes your application to run correctly, and load the older, mixed-mode assembly without issues. For full details on what’s happening here and why, I recommend reading Mark Miller’s detailed explanation of this attribute and the reasoning behind it. Before I show any code, let me say: I strongly recommend using the official approach of using app.config to set this policy. That being said, there are (rare) times when, for one reason or another, changing the application configuration file is less than ideal. While this is the supported approach to handling this issue, the CLR Hosting API includes a means of setting this programmatically via the ICLRRuntimeInfo interface. Normally, this is used if you’re hosting the CLR in a native application in order to set this, at runtime, prior to loading the assemblies. However, the F# Samples include a nice trick showing how to load this API and bind this policy, at runtime. This was required in order to host the Managed DirectX API, which is built against an older version of the CLR. This is fairly easy to port to C#. Instead of a direct port, I also added a little addition – by trapping the COM exception received if unable to bind (which will occur if the 2.0 CLR is already bound), I also allow a runtime check of whether this property was setup properly: public static class RuntimePolicyHelper { public static bool LegacyV2RuntimeEnabledSuccessfully { get; private set; } static RuntimePolicyHelper() { ICLRRuntimeInfo clrRuntimeInfo = (ICLRRuntimeInfo)RuntimeEnvironment.GetRuntimeInterfaceAsObject( Guid.Empty, typeof(ICLRRuntimeInfo).GUID); try { clrRuntimeInfo.BindAsLegacyV2Runtime(); LegacyV2RuntimeEnabledSuccessfully = true; } catch (COMException) { // This occurs with an HRESULT meaning // "A different runtime was already bound to the legacy CLR version 2 activation policy." LegacyV2RuntimeEnabledSuccessfully = false; } } [ComImport] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] [Guid("BD39D1D2-BA2F-486A-89B0-B4B0CB466891")] private interface ICLRRuntimeInfo { void xGetVersionString(); void xGetRuntimeDirectory(); void xIsLoaded(); void xIsLoadable(); void xLoadErrorString(); void xLoadLibrary(); void xGetProcAddress(); void xGetInterface(); void xSetDefaultStartupFlags(); void xGetDefaultStartupFlags(); [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)] void BindAsLegacyV2Runtime(); } } Using this, it’s possible to not only set this at runtime, but also verify, prior to loading your mixed mode assembly, whether this will succeed. In my case, this was quite useful – I am working on a library purely for internal use which uses a numerical package that is supplied with both a completely managed as well as a native solver. The native solver uses a CLR 2 mixed-mode assembly, but is dramatically faster than the pure managed approach. By checking RuntimePolicyHelper.LegacyV2RuntimeEnabledSuccessfully at runtime, I can decide whether to enable the native solver, and only do so if I successfully bound this policy. There are some tricks required here – To enable this sort of fallback behavior, you must make these checks in a type that doesn’t cause the mixed mode assembly to be loaded. In my case, this forced me to encapsulate the library I was using entirely in a separate class, perform the check, then pass through the required calls to that class. Otherwise, the library will load before the hosting process gets enabled, which in turn will fail. This code will also, of course, try to enable the runtime policy before the first time you use this class – which typically means just before the first time you check the boolean value. As a result, checking this early on in the application is more likely to allow it to work. Finally, if you’re using a library, this has to be called prior to the 2.0 CLR loading. This will cause it to fail if you try to use it to enable this policy in a plugin for most third party applications that don’t have their app.config setup properly, as they will likely have already loaded the 2.0 runtime. As an example, take a simple audio player. The code below shows how this can be used to properly, at runtime, only use the “native” API if this will succeed, and fallback (or raise a nicer exception) if this will fail: public class AudioPlayer { private IAudioEngine audioEngine; public AudioPlayer() { if (RuntimePolicyHelper.LegacyV2RuntimeEnabledSuccessfully) { // This will load a CLR 2 mixed mode assembly this.audioEngine = new AudioEngineNative(); } else { this.audioEngine = new AudioEngineManaged(); } } public void Play(string filename) { this.audioEngine.Play(filename); } } Now – the warning: This approach works, but I would be very hesitant to use it in public facing production code, especially for anything other than initializing your own application. While this should work in a library, using it has a very nasty side effect: you change the runtime policy of the executing application in a way that is very hidden and non-obvious.

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Data-driven animation states

- by user8363

I'm trying to handle animations in a 2D game engine hobby project, without hard-coding them. Hard coding animation states seems like a common but very strange phenomenon, to me. A little background: I'm working with an entity system where components are bags of data and subsystems act upon them. I chose to use a polling system to update animation states. With animation states I mean: "walking_left", "running_left", "walking_right", "shooting", ... My idea to handle animations was to design it as a data driven model. Data could be stored in an xml file, a rdbms, ... And could be loaded at the start of a game / level/ ... This way you can easily edit animations and transitions without having to go change the code everywhere in your game. As an example I made an xml draft of the data definitions I had in mind. One very important piece of data would simply be the description of an animation. An animation would have a unique id (a descriptive name). It would hold a reference id to an image (the sprite sheet it uses, because different animations may use different sprite sheets). The frames per second to run the animation on. The "replay" here defines if an animation should be run once or infinitely. Then I defined a list of rectangles as frames. <animation id='WIZARD_WALK_LEFT'> <image id='WIZARD_WALKING' /> <fps>50</fps> <replay>true</replay> <frames> <rectangle> <x>0</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> <rectangle> <x>45</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> </frames> </animation> Animation data would be loaded and held in an animation resource pool and referenced by game entities that are using it. It would be treated as a resource like an image, a sound, a texture, ... The second piece of data to define would be a state machine to handle animation states and transitions. This defines each state a game entity can be in, which states it can transition to and what triggers that state change. This state machine would differ from entity to entity. Because a bird might have states "walking" and "flying" while a human would only have the state "walking". However it could be shared by different entities because multiple humans will probably have the same states (especially when you define some common NPCs like monsters, etc). Additionally an orc might have the same states as a human. Just to demonstrate that this state definition might be shared but only by a select group of game entities. <state id='IDLE'> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_LEFT'> <event trigger='LEFT_UP' goto='IDLE' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_RIGHT'> <event trigger='RIGHT_UP' goto='IDLE' /> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> </state> These states can be handled by a polling system. Each game tick it grabs the current state of a game entity and checks all triggers. If a condition is met it changes the entity's state to the "goto" state. The last part I was struggling with was how to bind animation data and animation states to an entity. The most logical approach seemed to me to add a pointer to the state machine data an entity uses and to define for each state in that machine what animation it uses. Here is an xml example how I would define the animation behavior and graphical representation of some common entities in a game, by addressing animation state and animation data id. Note that both "wizard" and "orc" have the same animation states but a different animation. Also, a different animation could mean a different sprite sheet, or even a different sequence of animations (an animation could be longer or shorter). <entity name="wizard"> <state id="IDLE" animation="WIZARD_IDLE" /> <state id="MOVING_LEFT" animation="WIZARD_WALK_LEFT" /> </entity> <entity name="orc"> <state id="IDLE" animation="ORC_IDLE" /> <state id="MOVING_LEFT" animation="ORC_WALK_LEFT" /> </entity> When the entity is being created it would add a list of states with state machine data and an animation data reference. In the future I would use the entity system to build whole entities by defining components in a similar xml format. -- This is what I have come up with after some research. However I had some trouble getting my head around it, so I was hoping op some feedback. Is there something here what doesn't make sense, or is there a better way to handle these things? I grasped the idea of iterating through frames but I'm having trouble to take it a step further and this is my attempt to do that.

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Oracle Enterprise Manager 12c Ops Center Jump-Start for Partners

- by Get_Specialized!

Following the Normal 0 false false false EN-US X-NONE X-NONE Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} announcement at Oracle OpenWorld Tokyo, Partners can check out these resources to further learn about Oracle Enterprise Manager 12c Op Center and then use it to optimize your solution/services or offer new ones: Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; 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font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Making Infrastructure-as-a-Service in the Enterprise a Reality IDC report: Oracle Enterprise Manager 12c Embraces the Cloud with Integrated Lifecycle Management Follow-up webcast April 12th Total Cloud Control for Systems Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Oracle Enterprise Manager Ops Center 12c is no extra charge and included in the support contract of Oracle Systems customers.To learn more see the Ops Center Everywhere Program And if you're not already a member, be sure and join the Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; 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mysql: Cannot load from mysql.proc. The table is probably corrupted

- by Alex

Mysql was started: /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 but when I'm trying to do something: ERROR 1548 (HY000) at line 1: Cannot load from mysql.proc. The table is probably corrupted How to fix it? $ mysql -V mysql Ver 14.14 Distrib 5.1.58, for debian-linux-gnu (x86_64) using readline 6.2 $ lsb_release -a Distributor ID: Ubuntu Description: Ubuntu 11.10 Release: 11.10 Codename: oneiric $ sudo mysql_upgrade -uroot -p<password> --force Looking for 'mysql' as: mysql Looking for 'mysqlcheck' as: mysqlcheck Running 'mysqlcheck' with connection arguments: '--port=3306' '--socket=/var/run/mysqld/mysqld.sock' Running 'mysqlcheck' with connection arguments: '--port=3306' '--socket=/var/run/mysqld/mysqld.sock' mysql.columns_priv OK mysql.db OK mysql.event OK mysql.func OK mysql.general_log Error : You can't use locks with log tables. status : OK mysql.help_category OK mysql.help_keyword OK mysql.help_relation OK mysql.help_topic OK mysql.host OK mysql.ndb_binlog_index OK mysql.plugin OK mysql.proc OK mysql.procs_priv OK mysql.servers OK mysql.slow_log Error : You can't use locks with log tables. status : OK mysql.tables_priv OK mysql.time_zone OK mysql.time_zone_leap_second OK mysql.time_zone_name OK mysql.time_zone_transition OK mysql.time_zone_transition_type OK mysql.user OK Running 'mysql_fix_privilege_tables'... OK $ mysqlcheck --port=3700 --socket=/srv/mysql/sockets/mysql-my-env.sock -A -udata_owner -pdata_owner <all tables> OK UPD1: for example I'm trying to remove procedure: mysql> DROP PROCEDURE IF EXISTS mysql.myproc; ERROR 1548 (HY000): Cannot load from mysql.proc. The table is probably corrupted mysql> UPD2: mysql> REPAIR TABLE mysql.proc; +------------+--------+----------+-----------------------------------------------------------------------------------------+ | Table | Op | Msg_type | Msg_text | +------------+--------+----------+-----------------------------------------------------------------------------------------+ | mysql.proc | repair | error | 1 when fixing table | | mysql.proc | repair | Error | Can't change permissions of the file '/srv/mysql/myDB/mysql/proc.MYD' (Errcode: 1) | | mysql.proc | repair | status | Operation failed | +------------+--------+----------+-----------------------------------------------------------------------------------------+ 3 rows in set (0.04 sec) This is strange, because: $ ls -l /srv/mysql/myDB/mysql/proc.MYD -rwxrwxrwx 1 mysql root 3983252 2012-02-03 22:51 /srv/mysql/myDB/mysql/proc.MYD UPD3: $ ls -la /srv/mysql/myDB/mysql total 8930 drwxrwxrwx 2 mysql root 2480 2012-02-21 13:13 . drwxrwxrwx 13 mysql root 504 2012-02-21 19:01 .. -rwxrwxrwx 1 mysql root 8820 2012-02-20 15:50 columns_priv.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 columns_priv.MYD -rwxrwxrwx 1 mysql root 4096 2012-02-20 15:50 columns_priv.MYI -rwxrwxrwx 1 mysql root 9582 2012-02-20 15:50 db.frm -rwxrwxrwx 1 mysql root 8360 2011-12-08 02:14 db.MYD -rwxrwxrwx 1 mysql root 5120 2012-02-20 15:50 db.MYI -rwxrwxrwx 1 mysql root 54 2011-11-12 15:42 db.opt -rwxrwxrwx 1 mysql root 10223 2012-02-20 15:50 event.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 event.MYD -rwxrwxrwx 1 mysql root 2048 2012-02-20 15:50 event.MYI -rwxrwxrwx 1 mysql root 8665 2012-02-20 15:50 func.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 func.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 func.MYI -rwxrwxrwx 1 mysql root 8700 2012-02-20 15:50 help_category.frm -rwxrwxrwx 1 mysql root 21497 2011-11-12 15:42 help_category.MYD -rwxrwxrwx 1 mysql root 3072 2012-02-20 15:50 help_category.MYI -rwxrwxrwx 1 mysql root 8612 2012-02-20 15:50 help_keyword.frm -rwxrwxrwx 1 mysql root 88650 2011-11-12 15:42 help_keyword.MYD -rwxrwxrwx 1 mysql root 16384 2012-02-20 15:50 help_keyword.MYI -rwxrwxrwx 1 mysql root 8630 2012-02-20 15:50 help_relation.frm -rwxrwxrwx 1 mysql root 8874 2011-11-12 15:42 help_relation.MYD -rwxrwxrwx 1 mysql root 16384 2012-02-20 15:50 help_relation.MYI -rwxrwxrwx 1 mysql root 8770 2012-02-20 15:50 help_topic.frm -rwxrwxrwx 1 mysql root 414320 2011-11-12 15:42 help_topic.MYD -rwxrwxrwx 1 mysql root 20480 2012-02-20 15:50 help_topic.MYI -rwxrwxrwx 1 mysql root 9510 2012-02-20 15:50 host.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 host.MYD -rwxrwxrwx 1 mysql root 2048 2012-02-20 15:50 host.MYI -rwxrwxrwx 1 mysql root 8554 2011-11-12 15:42 innodb_monitor.frm -rwxrwxrwx 1 mysql root 98304 2011-11-12 15:55 innodb_monitor.ibd -rwxrwxrwx 1 mysql root 8592 2012-02-20 15:50 inventory.frm -rwxrwxrwx 1 mysql root 76 2011-11-12 15:42 inventory.MYD -rwxrwxrwx 1 mysql root 2048 2012-02-20 15:50 inventory.MYI -rwxrwxrwx 1 mysql root 8778 2012-02-20 15:50 ndb_binlog_index.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 ndb_binlog_index.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 ndb_binlog_index.MYI -rwxrwxrwx 1 mysql root 8586 2012-02-20 15:50 plugin.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 plugin.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 plugin.MYI -rwxrwxrwx 1 mysql root 9996 2012-02-20 15:50 proc.frm -rwxrwxrwx 1 mysql root 3983252 2012-02-03 22:51 proc.MYD -rwxrwxrwx 1 mysql root 36864 2012-02-21 13:23 proc.MYI -rwxrwxrwx 1 mysql root 8875 2012-02-20 15:50 procs_priv.frm -rwxrwxrwx 1 mysql root 1700 2011-11-12 15:42 procs_priv.MYD -rwxrwxrwx 1 mysql root 8192 2012-02-20 15:50 procs_priv.MYI -rwxrwxrwx 1 mysql root 3977704 2012-02-21 13:23 proc.TMD -rwxrwxrwx 1 mysql root 8800 2012-02-20 15:50 proxies_priv.frm -rwxrwxrwx 1 mysql root 693 2011-11-12 15:42 proxies_priv.MYD -rwxrwxrwx 1 mysql root 5120 2012-02-20 15:50 proxies_priv.MYI -rwxrwxrwx 1 mysql root 8838 2012-02-20 15:50 servers.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 servers.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 servers.MYI -rwxrwxrwx 1 mysql root 8955 2012-02-20 15:50 tables_priv.frm -rwxrwxrwx 1 mysql root 5957 2011-11-12 15:42 tables_priv.MYD -rwxrwxrwx 1 mysql root 8192 2012-02-20 15:50 tables_priv.MYI -rwxrwxrwx 1 mysql root 8636 2012-02-20 15:50 time_zone.frm -rwxrwxrwx 1 mysql root 8624 2012-02-20 15:50 time_zone_leap_second.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 time_zone_leap_second.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 time_zone_leap_second.MYI -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 time_zone.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 time_zone.MYI -rwxrwxrwx 1 mysql root 8606 2012-02-20 15:50 time_zone_name.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 time_zone_name.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 time_zone_name.MYI -rwxrwxrwx 1 mysql root 8686 2012-02-20 15:50 time_zone_transition.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 time_zone_transition.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 time_zone_transition.MYI -rwxrwxrwx 1 mysql root 8748 2012-02-20 15:50 time_zone_transition_type.frm -rwxrwxrwx 1 mysql root 0 2011-11-12 15:42 time_zone_transition_type.MYD -rwxrwxrwx 1 mysql root 1024 2012-02-20 15:50 time_zone_transition_type.MYI -rwxrwxrwx 1 mysql root 10630 2012-02-20 15:50 user.frm -rwxrwxrwx 1 mysql root 5456 2011-11-12 21:01 user.MYD -rwxrwxrwx 1 mysql root 4096 2012-02-20 15:50 user.MYI

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Parallelism in .NET – Part 3, Imperative Data Parallelism: Early Termination

- by Reed

Although simple data parallelism allows us to easily parallelize many of our iteration statements, there are cases that it does not handle well. In my previous discussion, I focused on data parallelism with no shared state, and where every element is being processed exactly the same. Unfortunately, there are many common cases where this does not happen. If we are dealing with a loop that requires early termination, extra care is required when parallelizing. Often, while processing in a loop, once a certain condition is met, it is no longer necessary to continue processing. This may be a matter of finding a specific element within the collection, or reaching some error case. The important distinction here is that, it is often impossible to know until runtime, what set of elements needs to be processed. In my initial discussion of data parallelism, I mentioned that this technique is a candidate when you can decompose the problem based on the data involved, and you wish to apply a single operation concurrently on all of the elements of a collection. This covers many of the potential cases, but sometimes, after processing some of the elements, we need to stop processing. As an example, lets go back to our previous Parallel.ForEach example with contacting a customer. However, this time, we’ll change the requirements slightly. In this case, we’ll add an extra condition – if the store is unable to email the customer, we will exit gracefully. The thinking here, of course, is that if the store is currently unable to email, the next time this operation runs, it will handle the same situation, so we can just skip our processing entirely. The original, serial case, with this extra condition, might look something like the following: foreach(var customer in customers) { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { // Exit gracefully if we fail to email, since this // entire process can be repeated later without issue. if (theStore.EmailCustomer(customer) == false) break; customer.LastEmailContact = DateTime.Now; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, we’re processing our loop, but at any point, if we fail to send our email successfully, we just abandon this process, and assume that it will get handled correctly the next time our routine is run. If we try to parallelize this using Parallel.ForEach, as we did previously, we’ll run into an error almost immediately: the break statement we’re using is only valid when enclosed within an iteration statement, such as foreach. When we switch to Parallel.ForEach, we’re no longer within an iteration statement – we’re a delegate running in a method. This needs to be handled slightly differently when parallelized. Instead of using the break statement, we need to utilize a new class in the Task Parallel Library: ParallelLoopState. The ParallelLoopState class is intended to allow concurrently running loop bodies a way to interact with each other, and provides us with a way to break out of a loop. In order to use this, we will use a different overload of Parallel.ForEach which takes an IEnumerable<T> and an Action<T, ParallelLoopState> instead of an Action<T>. Using this, we can parallelize the above operation by doing: Parallel.ForEach(customers, (customer, parallelLoopState) => { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { // Exit gracefully if we fail to email, since this // entire process can be repeated later without issue. if (theStore.EmailCustomer(customer) == false) parallelLoopState.Break(); else customer.LastEmailContact = DateTime.Now; } }); There are a couple of important points here. First, we didn’t actually instantiate the ParallelLoopState instance. It was provided directly to us via the Parallel class. All we needed to do was change our lambda expression to reflect that we want to use the loop state, and the Parallel class creates an instance for our use. We also needed to change our logic slightly when we call Break(). Since Break() doesn’t stop the program flow within our block, we needed to add an else case to only set the property in customer when we succeeded. This same technique can be used to break out of a Parallel.For loop. That being said, there is a huge difference between using ParallelLoopState to cause early termination and to use break in a standard iteration statement. When dealing with a loop serially, break will immediately terminate the processing within the closest enclosing loop statement. Calling ParallelLoopState.Break(), however, has a very different behavior. The issue is that, now, we’re no longer processing one element at a time. If we break in one of our threads, there are other threads that will likely still be executing. This leads to an important observation about termination of parallel code: Early termination in parallel routines is not immediate. Code will continue to run after you request a termination. This may seem problematic at first, but it is something you just need to keep in mind while designing your routine. ParallelLoopState.Break() should be thought of as a request. We are telling the runtime that no elements that were in the collection past the element we’re currently processing need to be processed, and leaving it up to the runtime to decide how to handle this as gracefully as possible. Although this may seem problematic at first, it is a good thing. If the runtime tried to immediately stop processing, many of our elements would be partially processed. It would be like putting a return statement in a random location throughout our loop body – which could have horrific consequences to our code’s maintainability. In order to understand and effectively write parallel routines, we, as developers, need a subtle, but profound shift in our thinking. We can no longer think in terms of sequential processes, but rather need to think in terms of requests to the system that may be handled differently than we’d first expect. This is more natural to developers who have dealt with asynchronous models previously, but is an important distinction when moving to concurrent programming models. As an example, I’ll discuss the Break() method. ParallelLoopState.Break() functions in a way that may be unexpected at first. When you call Break() from a loop body, the runtime will continue to process all elements of the collection that were found prior to the element that was being processed when the Break() method was called. This is done to keep the behavior of the Break() method as close to the behavior of the break statement as possible. We can see the behavior in this simple code: var collection = Enumerable.Range(0, 20); var pResult = Parallel.ForEach(collection, (element, state) => { if (element > 10) { Console.WriteLine("Breaking on {0}", element); state.Break(); } Console.WriteLine(element); }); If we run this, we get a result that may seem unexpected at first: 0 2 1 5 6 3 4 10 Breaking on 11 11 Breaking on 12 12 9 Breaking on 13 13 7 8 Breaking on 15 15 What is occurring here is that we loop until we find the first element where the element is greater than 10. In this case, this was found, the first time, when one of our threads reached element 11. It requested that the loop stop by calling Break() at this point. However, the loop continued processing until all of the elements less than 11 were completed, then terminated. This means that it will guarantee that elements 9, 7, and 8 are completed before it stops processing. You can see our other threads that were running each tried to break as well, but since Break() was called on the element with a value of 11, it decides which elements (0-10) must be processed. If this behavior is not desirable, there is another option. Instead of calling ParallelLoopState.Break(), you can call ParallelLoopState.Stop(). The Stop() method requests that the runtime terminate as soon as possible , without guaranteeing that any other elements are processed. Stop() will not stop the processing within an element, so elements already being processed will continue to be processed. It will prevent new elements, even ones found earlier in the collection, from being processed. Also, when Stop() is called, the ParallelLoopState’s IsStopped property will return true. This lets longer running processes poll for this value, and return after performing any necessary cleanup. The basic rule of thumb for choosing between Break() and Stop() is the following. Use ParallelLoopState.Stop() when possible, since it terminates more quickly. This is particularly useful in situations where you are searching for an element or a condition in the collection. Once you’ve found it, you do not need to do any other processing, so Stop() is more appropriate. Use ParallelLoopState.Break() if you need to more closely match the behavior of the C# break statement. Both methods behave differently than our C# break statement. Unfortunately, when parallelizing a routine, more thought and care needs to be put into every aspect of your routine than you may otherwise expect. This is due to my second observation: Parallelizing a routine will almost always change its behavior. This sounds crazy at first, but it’s a concept that’s so simple its easy to forget. We’re purposely telling the system to process more than one thing at the same time, which means that the sequence in which things get processed is no longer deterministic. It is easy to change the behavior of your routine in very subtle ways by introducing parallelism. Often, the changes are not avoidable, even if they don’t have any adverse side effects. This leads to my final observation for this post: Parallelization is something that should be handled with care and forethought, added by design, and not just introduced casually.

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Parallelism in .NET – Part 7, Some Differences between PLINQ and LINQ to Objects

- by Reed

In my previous post on Declarative Data Parallelism, I mentioned that PLINQ extends LINQ to Objects to support parallel operations. Although nearly all of the same operations are supported, there are some differences between PLINQ and LINQ to Objects. By introducing Parallelism to our declarative model, we add some extra complexity. This, in turn, adds some extra requirements that must be addressed. In order to illustrate the main differences, and why they exist, let’s begin by discussing some differences in how the two technologies operate, and look at the underlying types involved in LINQ to Objects and PLINQ . LINQ to Objects is mainly built upon a single class: Enumerable. The Enumerable class is a static class that defines a large set of extension methods, nearly all of which work upon an IEnumerable<T>. Many of these methods return a new IEnumerable<T>, allowing the methods to be chained together into a fluent style interface. This is what allows us to write statements that chain together, and lead to the nice declarative programming model of LINQ: double min = collection .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Other LINQ variants work in a similar fashion. For example, most data-oriented LINQ providers are built upon an implementation of IQueryable<T>, which allows the database provider to turn a LINQ statement into an underlying SQL query, to be performed directly on the remote database. PLINQ is similar, but instead of being built upon the Enumerable class, most of PLINQ is built upon a new static class: ParallelEnumerable. When using PLINQ, you typically begin with any collection which implements IEnumerable<T>, and convert it to a new type using an extension method defined on ParallelEnumerable: AsParallel(). This method takes any IEnumerable<T>, and converts it into a ParallelQuery<T>, the core class for PLINQ. There is a similar ParallelQuery class for working with non-generic IEnumerable implementations. This brings us to our first subtle, but important difference between PLINQ and LINQ – PLINQ always works upon specific types, which must be explicitly created. Typically, the type you’ll use with PLINQ is ParallelQuery<T>, but it can sometimes be a ParallelQuery or an OrderedParallelQuery<T>. Instead of dealing with an interface, implemented by an unknown class, we’re dealing with a specific class type. This works seamlessly from a usage standpoint – ParallelQuery<T> implements IEnumerable<T>, so you can always “switch back” to an IEnumerable<T>. The difference only arises at the beginning of our parallelization. When we’re using LINQ, and we want to process a normal collection via PLINQ, we need to explicitly convert the collection into a ParallelQuery<T> by calling AsParallel(). There is an important consideration here – AsParallel() does not need to be called on your specific collection, but rather any IEnumerable<T>. This allows you to place it anywhere in the chain of methods involved in a LINQ statement, not just at the beginning. This can be useful if you have an operation which will not parallelize well or is not thread safe. For example, the following is perfectly valid, and similar to our previous examples: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); However, if SomeOperation() is not thread safe, we could just as easily do: double min = collection .Select(item => item.SomeOperation()) .AsParallel() .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); In this case, we’re using standard LINQ to Objects for the Select(…) method, then converting the results of that map routine to a ParallelQuery<T>, and processing our filter (the Where method) and our aggregation (the Min method) in parallel. PLINQ also provides us with a way to convert a ParallelQuery<T> back into a standard IEnumerable<T>, forcing sequential processing via standard LINQ to Objects. If SomeOperation() was thread-safe, but PerformComputation() was not thread-safe, we would need to handle this by using the AsEnumerable() method: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .AsEnumerable() .Min(item => item.PerformComputation()); Here, we’re converting our collection into a ParallelQuery<T>, doing our map operation (the Select(…) method) and our filtering in parallel, then converting the collection back into a standard IEnumerable<T>, which causes our aggregation via Min() to be performed sequentially. This could also be written as two statements, as well, which would allow us to use the language integrated syntax for the first portion: var tempCollection = from item in collection.AsParallel() let e = item.SomeOperation() where (e.SomeProperty > 6 && e.SomeProperty < 24) select e; double min = tempCollection.AsEnumerable().Min(item => item.PerformComputation()); This allows us to use the standard LINQ style language integrated query syntax, but control whether it’s performed in parallel or serial by adding AsParallel() and AsEnumerable() appropriately. The second important difference between PLINQ and LINQ deals with order preservation. PLINQ, by default, does not preserve the order of of source collection. This is by design. In order to process a collection in parallel, the system needs to naturally deal with multiple elements at the same time. Maintaining the original ordering of the sequence adds overhead, which is, in many cases, unnecessary. Therefore, by default, the system is allowed to completely change the order of your sequence during processing. If you are doing a standard query operation, this is usually not an issue. However, there are times when keeping a specific ordering in place is important. If this is required, you can explicitly request the ordering be preserved throughout all operations done on a ParallelQuery<T> by using the AsOrdered() extension method. This will cause our sequence ordering to be preserved. For example, suppose we wanted to take a collection, perform an expensive operation which converts it to a new type, and display the first 100 elements. In LINQ to Objects, our code might look something like: // Using IEnumerable<SourceClass> collection IEnumerable<ResultClass> results = collection .Select(e => e.CreateResult()) .Take(100); If we just converted this to a parallel query naively, like so: IEnumerable<ResultClass> results = collection .AsParallel() .Select(e => e.CreateResult()) .Take(100); We could very easily get a very different, and non-reproducable, set of results, since the ordering of elements in the input collection is not preserved. To get the same results as our original query, we need to use: IEnumerable<ResultClass> results = collection .AsParallel() .AsOrdered() .Select(e => e.CreateResult()) .Take(100); This requests that PLINQ process our sequence in a way that verifies that our resulting collection is ordered as if it were processed serially. This will cause our query to run slower, since there is overhead involved in maintaining the ordering. However, in this case, it is required, since the ordering is required for correctness. PLINQ is incredibly useful. It allows us to easily take nearly any LINQ to Objects query and run it in parallel, using the same methods and syntax we’ve used previously. There are some important differences in operation that must be considered, however – it is not a free pass to parallelize everything. When using PLINQ in order to parallelize your routines declaratively, the same guideline I mentioned before still applies: Parallelization is something that should be handled with care and forethought, added by design, and not just introduced casually.

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Parallelism in .NET – Part 9, Configuration in PLINQ and TPL

- by Reed

Parallel LINQ and the Task Parallel Library contain many options for configuration. Although the default configuration options are often ideal, there are times when customizing the behavior is desirable. Both frameworks provide full configuration support. When working with Data Parallelism, there is one primary configuration option we often need to control – the number of threads we want the system to use when parallelizing our routine. By default, PLINQ and the TPL both use the ThreadPool to schedule tasks. Given the major improvements in the ThreadPool in CLR 4, this default behavior is often ideal. However, there are times that the default behavior is not appropriate. For example, if you are working on multiple threads simultaneously, and want to schedule parallel operations from within both threads, you might want to consider restricting each parallel operation to using a subset of the processing cores of the system. Not doing this might over-parallelize your routine, which leads to inefficiencies from having too many context switches. In the Task Parallel Library, configuration is handled via the ParallelOptions class. All of the methods of the Parallel class have an overload which accepts a ParallelOptions argument. We configure the Parallel class by setting the ParallelOptions.MaxDegreeOfParallelism property. For example, let’s revisit one of the simple data parallel examples from Part 2: Parallel.For(0, pixelData.GetUpperBound(0), row => { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, we’re looping through an image, and calling a method on each pixel in the image. If this was being done on a separate thread, and we knew another thread within our system was going to be doing a similar operation, we likely would want to restrict this to using half of the cores on the system. This could be accomplished easily by doing: var options = new ParallelOptions(); options.MaxDegreeOfParallelism = Math.Max(Environment.ProcessorCount / 2, 1); Parallel.For(0, pixelData.GetUpperBound(0), options, row => { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } }); Now, we’re restricting this routine to using no more than half the cores in our system. Note that I included a check to prevent a single core system from supplying zero; without this check, we’d potentially cause an exception. I also did not hard code a specific value for the MaxDegreeOfParallelism property. One of our goals when parallelizing a routine is allowing it to scale on better hardware. Specifying a hard-coded value would contradict that goal. Parallel LINQ also supports configuration, and in fact, has quite a few more options for configuring the system. The main configuration option we most often need is the same as our TPL option: we need to supply the maximum number of processing threads. In PLINQ, this is done via a new extension method on ParallelQuery<T>: ParallelEnumerable.WithDegreeOfParallelism. Let’s revisit our declarative data parallelism sample from Part 6: double min = collection.AsParallel().Min(item => item.PerformComputation()); Here, we’re performing a computation on each element in the collection, and saving the minimum value of this operation. If we wanted to restrict this to a limited number of threads, we would add our new extension method: int maxThreads = Math.Max(Environment.ProcessorCount / 2, 1); double min = collection .AsParallel() .WithDegreeOfParallelism(maxThreads) .Min(item => item.PerformComputation()); This automatically restricts the PLINQ query to half of the threads on the system. PLINQ provides some additional configuration options. By default, PLINQ will occasionally revert to processing a query in parallel. This occurs because many queries, if parallelized, typically actually cause an overall slowdown compared to a serial processing equivalent. By analyzing the “shape” of the query, PLINQ often decides to run a query serially instead of in parallel. This can occur for (taken from MSDN): Queries that contain a Select, indexed Where, indexed SelectMany, or ElementAt clause after an ordering or filtering operator that has removed or rearranged original indices. Queries that contain a Take, TakeWhile, Skip, SkipWhile operator and where indices in the source sequence are not in the original order. Queries that contain Zip or SequenceEquals, unless one of the data sources has an originally ordered index and the other data source is indexable (i.e. an array or IList(T)). Queries that contain Concat, unless it is applied to indexable data sources. Queries that contain Reverse, unless applied to an indexable data source. If the specific query follows these rules, PLINQ will run the query on a single thread. However, none of these rules look at the specific work being done in the delegates, only at the “shape” of the query. There are cases where running in parallel may still be beneficial, even if the shape is one where it typically parallelizes poorly. In these cases, you can override the default behavior by using the WithExecutionMode extension method. This would be done like so: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .Select(i => i.PerformComputation()) .Reverse(); Here, the default behavior would be to not parallelize the query unless collection implemented IList<T>. We can force this to run in parallel by adding the WithExecutionMode extension method in the method chain. Finally, PLINQ has the ability to configure how results are returned. When a query is filtering or selecting an input collection, the results will need to be streamed back into a single IEnumerable<T> result. For example, the method above returns a new, reversed collection. In this case, the processing of the collection will be done in parallel, but the results need to be streamed back to the caller serially, so they can be enumerated on a single thread. This streaming introduces overhead. IEnumerable<T> isn’t designed with thread safety in mind, so the system needs to handle merging the parallel processes back into a single stream, which introduces synchronization issues. There are two extremes of how this could be accomplished, but both extremes have disadvantages. The system could watch each thread, and whenever a thread produces a result, take that result and send it back to the caller. This would mean that the calling thread would have access to the data as soon as data is available, which is the benefit of this approach. However, it also means that every item is introducing synchronization overhead, since each item needs to be merged individually. On the other extreme, the system could wait until all of the results from all of the threads were ready, then push all of the results back to the calling thread in one shot. The advantage here is that the least amount of synchronization is added to the system, which means the query will, on a whole, run the fastest. However, the calling thread will have to wait for all elements to be processed, so this could introduce a long delay between when a parallel query begins and when results are returned. The default behavior in PLINQ is actually between these two extremes. By default, PLINQ maintains an internal buffer, and chooses an optimal buffer size to maintain. Query results are accumulated into the buffer, then returned in the IEnumerable<T> result in chunks. This provides reasonably fast access to the results, as well as good overall throughput, in most scenarios. However, if we know the nature of our algorithm, we may decide we would prefer one of the other extremes. This can be done by using the WithMergeOptions extension method. For example, if we know that our PerformComputation() routine is very slow, but also variable in runtime, we may want to retrieve results as they are available, with no bufferring. This can be done by changing our above routine to: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .WithMergeOptions(ParallelMergeOptions.NotBuffered) .Select(i => i.PerformComputation()) .Reverse(); On the other hand, if are already on a background thread, and we want to allow the system to maximize its speed, we might want to allow the system to fully buffer the results: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .WithMergeOptions(ParallelMergeOptions.FullyBuffered) .Select(i => i.PerformComputation()) .Reverse(); Notice, also, that you can specify multiple configuration options in a parallel query. By chaining these extension methods together, we generate a query that will always run in parallel, and will always complete before making the results available in our IEnumerable<T>.

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Parallelism in .NET – Part 2, Simple Imperative Data Parallelism

- by Reed

In my discussion of Decomposition of the problem space, I mentioned that Data Decomposition is often the simplest abstraction to use when trying to parallelize a routine. If a problem can be decomposed based off the data, we will often want to use what MSDN refers to as Data Parallelism as our strategy for implementing our routine. The Task Parallel Library in .NET 4 makes implementing Data Parallelism, for most cases, very simple. Data Parallelism is the main technique we use to parallelize a routine which can be decomposed based off data. Data Parallelism refers to taking a single collection of data, and having a single operation be performed concurrently on elements in the collection. One side note here: Data Parallelism is also sometimes referred to as the Loop Parallelism Pattern or Loop-level Parallelism. In general, for this series, I will try to use the terminology used in the MSDN Documentation for the Task Parallel Library. This should make it easier to investigate these topics in more detail. Once we’ve determined we have a problem that, potentially, can be decomposed based on data, implementation using Data Parallelism in the TPL is quite simple. Let’s take our example from the Data Decomposition discussion – a simple contrast stretching filter. Here, we have a collection of data (pixels), and we need to run a simple operation on each element of the pixel. Once we know the minimum and maximum values, we most likely would have some simple code like the following: for (int row=0; row < pixelData.GetUpperBound(0); ++row) { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This simple routine loops through a two dimensional array of pixelData, and calls the AdjustContrast routine on each pixel. As I mentioned, when you’re decomposing a problem space, most iteration statements are potentially candidates for data decomposition. Here, we’re using two for loops – one looping through rows in the image, and a second nested loop iterating through the columns. We then perform one, independent operation on each element based on those loop positions. This is a prime candidate – we have no shared data, no dependencies on anything but the pixel which we want to change. Since we’re using a for loop, we can easily parallelize this using the Parallel.For method in the TPL: Parallel.For(0, pixelData.GetUpperBound(0), row => { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } }); Here, by simply changing our first for loop to a call to Parallel.For, we can parallelize this portion of our routine. Parallel.For works, as do many methods in the TPL, by creating a delegate and using it as an argument to a method. In this case, our for loop iteration block becomes a delegate creating via a lambda expression. This lets you write code that, superficially, looks similar to the familiar for loop, but functions quite differently at runtime. We could easily do this to our second for loop as well, but that may not be a good idea. There is a balance to be struck when writing parallel code. We want to have enough work items to keep all of our processors busy, but the more we partition our data, the more overhead we introduce. In this case, we have an image of data – most likely hundreds of pixels in both dimensions. By just parallelizing our first loop, each row of pixels can be run as a single task. With hundreds of rows of data, we are providing fine enough granularity to keep all of our processors busy. If we parallelize both loops, we’re potentially creating millions of independent tasks. This introduces extra overhead with no extra gain, and will actually reduce our overall performance. This leads to my first guideline when writing parallel code: Partition your problem into enough tasks to keep each processor busy throughout the operation, but not more than necessary to keep each processor busy. Also note that I parallelized the outer loop. I could have just as easily partitioned the inner loop. However, partitioning the inner loop would have led to many more discrete work items, each with a smaller amount of work (operate on one pixel instead of one row of pixels). My second guideline when writing parallel code reflects this: Partition your problem in a way to place the most work possible into each task. This typically means, in practice, that you will want to parallelize the routine at the “highest” point possible in the routine, typically the outermost loop. If you’re looking at parallelizing methods which call other methods, you’ll want to try to partition your work high up in the stack – as you get into lower level methods, the performance impact of parallelizing your routines may not overcome the overhead introduced. Parallel.For works great for situations where we know the number of elements we’re going to process in advance. If we’re iterating through an IList<T> or an array, this is a typical approach. However, there are other iteration statements common in C#. In many situations, we’ll use foreach instead of a for loop. This can be more understandable and easier to read, but also has the advantage of working with collections which only implement IEnumerable<T>, where we do not know the number of elements involved in advance. As an example, lets take the following situation. Say we have a collection of Customers, and we want to iterate through each customer, check some information about the customer, and if a certain case is met, send an email to the customer and update our instance to reflect this change. Normally, this might look something like: foreach(var customer in customers) { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { theStore.EmailCustomer(customer); customer.LastEmailContact = DateTime.Now; } } Here, we’re doing a fair amount of work for each customer in our collection, but we don’t know how many customers exist. If we assume that theStore.GetLastContact(customer) and theStore.EmailCustomer(customer) are both side-effect free, thread safe operations, we could parallelize this using Parallel.ForEach: Parallel.ForEach(customers, customer => { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { theStore.EmailCustomer(customer); customer.LastEmailContact = DateTime.Now; } }); Just like Parallel.For, we rework our loop into a method call accepting a delegate created via a lambda expression. This keeps our new code very similar to our original iteration statement, however, this will now execute in parallel. The same guidelines apply with Parallel.ForEach as with Parallel.For. The other iteration statements, do and while, do not have direct equivalents in the Task Parallel Library. These, however, are very easy to implement using Parallel.ForEach and the yield keyword. Most applications can benefit from implementing some form of Data Parallelism. Iterating through collections and performing “work” is a very common pattern in nearly every application. When the problem can be decomposed by data, we often can parallelize the workload by merely changing foreach statements to Parallel.ForEach method calls, and for loops to Parallel.For method calls. Any time your program operates on a collection, and does a set of work on each item in the collection where that work is not dependent on other information, you very likely have an opportunity to parallelize your routine.

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Parallelism in .NET – Part 4, Imperative Data Parallelism: Aggregation

- by Reed

In the article on simple data parallelism, I described how to perform an operation on an entire collection of elements in parallel. Often, this is not adequate, as the parallel operation is going to be performing some form of aggregation. Simple examples of this might include taking the sum of the results of processing a function on each element in the collection, or finding the minimum of the collection given some criteria. This can be done using the techniques described in simple data parallelism, however, special care needs to be taken into account to synchronize the shared data appropriately. The Task Parallel Library has tools to assist in this synchronization. The main issue with aggregation when parallelizing a routine is that you need to handle synchronization of data. Since multiple threads will need to write to a shared portion of data. Suppose, for example, that we wanted to parallelize a simple loop that looked for the minimum value within a dataset: double min = double.MaxValue; foreach(var item in collection) { double value = item.PerformComputation(); min = System.Math.Min(min, value); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This seems like a good candidate for parallelization, but there is a problem here. If we just wrap this into a call to Parallel.ForEach, we’ll introduce a critical race condition, and get the wrong answer. Let’s look at what happens here: // Buggy code! Do not use! double min = double.MaxValue; Parallel.ForEach(collection, item => { double value = item.PerformComputation(); min = System.Math.Min(min, value); }); This code has a fatal flaw: min will be checked, then set, by multiple threads simultaneously. Two threads may perform the check at the same time, and set the wrong value for min. Say we get a value of 1 in thread 1, and a value of 2 in thread 2, and these two elements are the first two to run. If both hit the min check line at the same time, both will determine that min should change, to 1 and 2 respectively. If element 1 happens to set the variable first, then element 2 sets the min variable, we’ll detect a min value of 2 instead of 1. This can lead to wrong answers. Unfortunately, fixing this, with the Parallel.ForEach call we’re using, would require adding locking. We would need to rewrite this like: // Safe, but slow double min = double.MaxValue; // Make a "lock" object object syncObject = new object(); Parallel.ForEach(collection, item => { double value = item.PerformComputation(); lock(syncObject) min = System.Math.Min(min, value); }); This will potentially add a huge amount of overhead to our calculation. Since we can potentially block while waiting on the lock for every single iteration, we will most likely slow this down to where it is actually quite a bit slower than our serial implementation. The problem is the lock statement – any time you use lock(object), you’re almost assuring reduced performance in a parallel situation. This leads to two observations I’ll make: When parallelizing a routine, try to avoid locks. That being said: Always add any and all required synchronization to avoid race conditions. These two observations tend to be opposing forces – we often need to synchronize our algorithms, but we also want to avoid the synchronization when possible. Looking at our routine, there is no way to directly avoid this lock, since each element is potentially being run on a separate thread, and this lock is necessary in order for our routine to function correctly every time. However, this isn’t the only way to design this routine to implement this algorithm. Realize that, although our collection may have thousands or even millions of elements, we have a limited number of Processing Elements (PE). Processing Element is the standard term for a hardware element which can process and execute instructions. This typically is a core in your processor, but many modern systems have multiple hardware execution threads per core. The Task Parallel Library will not execute the work for each item in the collection as a separate work item. Instead, when Parallel.ForEach executes, it will partition the collection into larger “chunks” which get processed on different threads via the ThreadPool. This helps reduce the threading overhead, and help the overall speed. In general, the Parallel class will only use one thread per PE in the system. Given the fact that there are typically fewer threads than work items, we can rethink our algorithm design. We can parallelize our algorithm more effectively by approaching it differently. Because the basic aggregation we are doing here (Min) is communitive, we do not need to perform this in a given order. We knew this to be true already – otherwise, we wouldn’t have been able to parallelize this routine in the first place. With this in mind, we can treat each thread’s work independently, allowing each thread to serially process many elements with no locking, then, after all the threads are complete, “merge” together the results. This can be accomplished via a different set of overloads in the Parallel class: Parallel.ForEach<TSource,TLocal>. The idea behind these overloads is to allow each thread to begin by initializing some local state (TLocal). The thread will then process an entire set of items in the source collection, providing that state to the delegate which processes an individual item. Finally, at the end, a separate delegate is run which allows you to handle merging that local state into your final results. To rewriting our routine using Parallel.ForEach<TSource,TLocal>, we need to provide three delegates instead of one. The most basic version of this function is declared as: public static ParallelLoopResult ForEach<TSource, TLocal>( IEnumerable<TSource> source, Func<TLocal> localInit, Func<TSource, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally ) The first delegate (the localInit argument) is defined as Func<TLocal>. This delegate initializes our local state. It should return some object we can use to track the results of a single thread’s operations. The second delegate (the body argument) is where our main processing occurs, although now, instead of being an Action<T>, we actually provide a Func<TSource, ParallelLoopState, TLocal, TLocal> delegate. This delegate will receive three arguments: our original element from the collection (TSource), a ParallelLoopState which we can use for early termination, and the instance of our local state we created (TLocal). It should do whatever processing you wish to occur per element, then return the value of the local state after processing is completed. The third delegate (the localFinally argument) is defined as Action<TLocal>. This delegate is passed our local state after it’s been processed by all of the elements this thread will handle. This is where you can merge your final results together. This may require synchronization, but now, instead of synchronizing once per element (potentially millions of times), you’ll only have to synchronize once per thread, which is an ideal situation. Now that I’ve explained how this works, lets look at the code: // Safe, and fast! double min = double.MaxValue; // Make a "lock" object object syncObject = new object(); Parallel.ForEach( collection, // First, we provide a local state initialization delegate. () => double.MaxValue, // Next, we supply the body, which takes the original item, loop state, // and local state, and returns a new local state (item, loopState, localState) => { double value = item.PerformComputation(); return System.Math.Min(localState, value); }, // Finally, we provide an Action<TLocal>, to "merge" results together localState => { // This requires locking, but it's only once per used thread lock(syncObj) min = System.Math.Min(min, localState); } ); Although this is a bit more complicated than the previous version, it is now both thread-safe, and has minimal locking. This same approach can be used by Parallel.For, although now, it’s Parallel.For<TLocal>. When working with Parallel.For<TLocal>, you use the same triplet of delegates, with the same purpose and results. Also, many times, you can completely avoid locking by using a method of the Interlocked class to perform the final aggregation in an atomic operation. The MSDN example demonstrating this same technique using Parallel.For uses the Interlocked class instead of a lock, since they are doing a sum operation on a long variable, which is possible via Interlocked.Add. By taking advantage of local state, we can use the Parallel class methods to parallelize algorithms such as aggregation, which, at first, may seem like poor candidates for parallelization. Doing so requires careful consideration, and often requires a slight redesign of the algorithm, but the performance gains can be significant if handled in a way to avoid excessive synchronization.

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Parallelism in .NET – Part 11, Divide and Conquer via Parallel.Invoke

- by Reed

Many algorithms are easily written to work via recursion. For example, most data-oriented tasks where a tree of data must be processed are much more easily handled by starting at the root, and recursively “walking” the tree. Some algorithms work this way on flat data structures, such as arrays, as well. This is a form of divide and conquer: an algorithm design which is based around breaking up a set of work recursively, “dividing” the total work in each recursive step, and “conquering” the work when the remaining work is small enough to be solved easily. Recursive algorithms, especially ones based on a form of divide and conquer, are often a very good candidate for parallelization. This is apparent from a common sense standpoint. Since we’re dividing up the total work in the algorithm, we have an obvious, built-in partitioning scheme. Once partitioned, the data can be worked upon independently, so there is good, clean isolation of data. Implementing this type of algorithm is fairly simple. The Parallel class in .NET 4 includes a method suited for this type of operation: Parallel.Invoke. This method works by taking any number of delegates defined as an Action, and operating them all in parallel. The method returns when every delegate has completed: Parallel.Invoke( () => { Console.WriteLine("Action 1 executing in thread {0}", Thread.CurrentThread.ManagedThreadId); }, () => { Console.WriteLine("Action 2 executing in thread {0}", Thread.CurrentThread.ManagedThreadId); }, () => { Console.WriteLine("Action 3 executing in thread {0}", Thread.CurrentThread.ManagedThreadId); } ); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Running this simple example demonstrates the ease of using this method. For example, on my system, I get three separate thread IDs when running the above code. By allowing any number of delegates to be executed directly, concurrently, the Parallel.Invoke method provides us an easy way to parallelize any algorithm based on divide and conquer. We can divide our work in each step, and execute each task in parallel, recursively. For example, suppose we wanted to implement our own quicksort routine. The quicksort algorithm can be designed based on divide and conquer. In each iteration, we pick a pivot point, and use that to partition the total array. We swap the elements around the pivot, then recursively sort the lists on each side of the pivot. For example, let’s look at this simple, sequential implementation of quicksort: public static void QuickSort<T>(T[] array) where T : IComparable<T> { QuickSortInternal(array, 0, array.Length - 1); } private static void QuickSortInternal<T>(T[] array, int left, int right) where T : IComparable<T> { if (left >= right) { return; } SwapElements(array, left, (left + right) / 2); int last = left; for (int current = left + 1; current <= right; ++current) { if (array[current].CompareTo(array[left]) < 0) { ++last; SwapElements(array, last, current); } } SwapElements(array, left, last); QuickSortInternal(array, left, last - 1); QuickSortInternal(array, last + 1, right); } static void SwapElements<T>(T[] array, int i, int j) { T temp = array[i]; array[i] = array[j]; array[j] = temp; } Here, we implement the quicksort algorithm in a very common, divide and conquer approach. Running this against the built-in Array.Sort routine shows that we get the exact same answers (although the framework’s sort routine is slightly faster). On my system, for example, I can use framework’s sort to sort ten million random doubles in about 7.3s, and this implementation takes about 9.3s on average. Looking at this routine, though, there is a clear opportunity to parallelize. At the end of QuickSortInternal, we recursively call into QuickSortInternal with each partition of the array after the pivot is chosen. This can be rewritten to use Parallel.Invoke by simply changing it to: // Code above is unchanged... SwapElements(array, left, last); Parallel.Invoke( () => QuickSortInternal(array, left, last - 1), () => QuickSortInternal(array, last + 1, right) ); } This routine will now run in parallel. When executing, we now see the CPU usage across all cores spike while it executes. However, there is a significant problem here – by parallelizing this routine, we took it from an execution time of 9.3s to an execution time of approximately 14 seconds! We’re using more resources as seen in the CPU usage, but the overall result is a dramatic slowdown in overall processing time. This occurs because parallelization adds overhead. Each time we split this array, we spawn two new tasks to parallelize this algorithm! This is far, far too many tasks for our cores to operate upon at a single time. In effect, we’re “over-parallelizing” this routine. This is a common problem when working with divide and conquer algorithms, and leads to an important observation: When parallelizing a recursive routine, take special care not to add more tasks than necessary to fully utilize your system. This can be done with a few different approaches, in this case. Typically, the way to handle this is to stop parallelizing the routine at a certain point, and revert back to the serial approach. Since the first few recursions will all still be parallelized, our “deeper” recursive tasks will be running in parallel, and can take full advantage of the machine. This also dramatically reduces the overhead added by parallelizing, since we’re only adding overhead for the first few recursive calls. There are two basic approaches we can take here. The first approach would be to look at the total work size, and if it’s smaller than a specific threshold, revert to our serial implementation. In this case, we could just check right-left, and if it’s under a threshold, call the methods directly instead of using Parallel.Invoke. The second approach is to track how “deep” in the “tree” we are currently at, and if we are below some number of levels, stop parallelizing. This approach is a more general-purpose approach, since it works on routines which parse trees as well as routines working off of a single array, but may not work as well if a poor partitioning strategy is chosen or the tree is not balanced evenly. This can be written very easily. If we pass a maxDepth parameter into our internal routine, we can restrict the amount of times we parallelize by changing the recursive call to: // Code above is unchanged... SwapElements(array, left, last); if (maxDepth < 1) { QuickSortInternal(array, left, last - 1, maxDepth); QuickSortInternal(array, last + 1, right, maxDepth); } else { --maxDepth; Parallel.Invoke( () => QuickSortInternal(array, left, last - 1, maxDepth), () => QuickSortInternal(array, last + 1, right, maxDepth)); } We no longer allow this to parallelize indefinitely – only to a specific depth, at which time we revert to a serial implementation. By starting the routine with a maxDepth equal to Environment.ProcessorCount, we can restrict the total amount of parallel operations significantly, but still provide adequate work for each processing core. With this final change, my timings are much better. On average, I get the following timings: Framework via Array.Sort: 7.3 seconds Serial Quicksort Implementation: 9.3 seconds Naive Parallel Implementation: 14 seconds Parallel Implementation Restricting Depth: 4.7 seconds Finally, we are now faster than the framework’s Array.Sort implementation.

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Building and Deploying Windows Azure Web Sites using Git and GitHub for Windows

- by shiju

Microsoft Windows Azure team has released a new version of Windows Azure which is providing many excellent features. The new Windows Azure provides Web Sites which allows you to deploy up to 10 web sites for free in a multitenant shared environment and you can easily upgrade this web site to a private, dedicated virtual server when the traffic is grows. The Meet Windows Azure Fact Sheet provides the following information about a Windows Azure Web Site: Windows Azure Web Sites enable developers to easily build and deploy websites with support for multiple frameworks and popular open source applications, including ASP.NET, PHP and Node.js. With just a few clicks, developers can take advantage of Windows Azure’s global scale without having to worry about operations, servers or infrastructure. It is easy to deploy existing sites, if they run on Internet Information Services (IIS) 7, or to build new sites, with a free offer of 10 websites upon signup, with the ability to scale up as needed with reserved instances. Windows Azure Web Sites includes support for the following: Multiple frameworks including ASP.NET, PHP and Node.js Popular open source software apps including WordPress, Joomla!, Drupal, Umbraco and DotNetNuke Windows Azure SQL Database and MySQL databases Multiple types of developer tools and protocols including Visual Studio, Git, FTP, Visual Studio Team Foundation Services and Microsoft WebMatrix Signup to Windows and Enable Azure Web Sites You can signup for a 90 days free trial account in Windows Azure from here. After creating an account in Windows Azure, go to https://account.windowsazure.com/ , and select to preview features to view the available previews. In the Web Sites section of the preview features, click “try it now” which will enables the web sites feature Create Web Site in Windows Azure To create a web sites, login to the Windows Azure portal, and select Web Sites from and click New icon from the left corner Click WEB SITE, QUICK CREATE and put values for URL and REGION dropdown. You can see the all web sites from the dashboard of the Windows Azure portal Set up Git Publishing Select your web site from the dashboard, and select Set up Git publishing To enable Git publishing , you must give user name and password which will initialize a Git repository Clone Git Repository We can use GitHub for Windows to publish apps to non-GitHub repositories which is well explained by Phil Haack on his blog post. Here we are going to deploy the web site using GitHub for Windows. Let’s clone a Git repository using the Git Url which will be getting from the Windows Azure portal. Let’s copy the Git url and execute the “git clone” with the git url. You can use the Git Shell provided by GitHub for Windows. To get it, right on the GitHub for Windows, and select open shell here as shown in the below picture. When executing the Git Clone command, it will ask for a password where you have to give password which specified in the Windows Azure portal. After cloning the GIT repository, you can drag and drop the local Git repository folder to GitHub for Windows GUI. This will automatically add the Windows Azure Web Site repository onto GitHub for Windows where you can commit your changes and publish your web sites to Windows Azure. Publish the Web Site using GitHub for Windows We can add multiple framework level files including ASP.NET, PHP and Node.js, to the local repository folder can easily publish to Windows Azure from GitHub for Windows GUI. For this demo, let me just add a simple Node.js file named Server.js which handles few request handlers. 1: var http = require('http'); 2: var port=process.env.PORT; 3: var querystring = require('querystring'); 4: var utils = require('util'); 5: var url = require("url"); 6: 7: var server = http.createServer(function(req, res) { 8: switch (req.url) { //checking the request url 9: case '/': 10: homePageHandler (req, res); //handler for home page 11: break; 12: case '/register': 13: registerFormHandler (req, res);//hamdler for register 14: break; 15: default: 16: nofoundHandler (req, res);// handler for 404 not found 17: break; 18: } 19: }); 20: server.listen(port); 21: //function to display the html form 22: function homePageHandler (req, res) { 23: console.log('Request handler home was called.'); 24: res.writeHead(200, {'Content-Type': 'text/html'}); 25: var body = '<html>'+ 26: '<head>'+ 27: '<meta http-equiv="Content-Type" content="text/html; '+ 28: 'charset=UTF-8" />'+ 29: '</head>'+ 30: '<body>'+ 31: '<form action="/register" method="post">'+ 32: 'Name:<input type=text value="" name="name" size=15></br>'+ 33: 'Email:<input type=text value="" name="email" size=15></br>'+ 34: '<input type="submit" value="Submit" />'+ 35: '</form>'+ 36: '</body>'+ 37: '</html>'; 38: //response content 39: res.end(body); 40: } 41: //handler for Post request 42: function registerFormHandler (req, res) { 43: console.log('Request handler register was called.'); 44: var pathname = url.parse(req.url).pathname; 45: console.log("Request for " + pathname + " received."); 46: var postData = ""; 47: req.on('data', function(chunk) { 48: // append the current chunk of data to the postData variable 49: postData += chunk.toString(); 50: }); 51: req.on('end', function() { 52: // doing something with the posted data 53: res.writeHead(200, "OK", {'Content-Type': 'text/html'}); 54: // parse the posted data 55: var decodedBody = querystring.parse(postData); 56: // output the decoded data to the HTTP response 57: res.write('<html><head><title>Post data</title></head><body><pre>'); 58: res.write(utils.inspect(decodedBody)); 59: res.write('</pre></body></html>'); 60: res.end(); 61: }); 62: } 63: //Error handler for 404 no found 64: function nofoundHandler(req, res) { 65: console.log('Request handler nofound was called.'); 66: res.writeHead(404, {'Content-Type': 'text/plain'}); 67: res.end('404 Error - Request handler not found'); 68: } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } If there is any change in the local repository folder, GitHub for Windows will automatically detect the changes. In the above step, we have just added a Server.js file so that GitHub for Windows will detect the changes. Let’s commit the changes to the local repository before publishing the web site to Windows Azure. After committed the all changes, you can click publish button which will publish the all changes to Windows Azure repository. The following screen shot shows deployment history from the Windows Azure portal. GitHub for Windows is providing a sync button which can use for synchronizing between local repository and Windows Azure repository after making any commit on the local repository after any changes. Our web site is running after the deployment using Git Summary Windows Azure Web Sites lets the developers to easily build and deploy websites with support for multiple framework including ASP.NET, PHP and Node.js and can easily deploy the Web Sites using Visual Studio, Git, FTP, Visual Studio Team Foundation Services and Microsoft WebMatrix. In this demo, we have deployed a Node.js Web Site to Windows Azure using Git. We can use GitHub for Windows to publish apps to non-GitHub repositories and can use to publish Web SItes to Windows Azure.

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