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  • ASP.NET custom templates, still ASP.NET controls possible?

    - by Sha Le
    Hello: we currently do not use asp.net controls (no web forms). The way we do is: 1 Read HTML file from disk 2 lookup database, parse tags and populate data finally, Response.Write(page.ToString()); here there is no possibility of using asp.net controls. What I am wondering is, if we use asp.net controls in those HTML files, is there way to process them during step 2? Thanks and appreciate your response.

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  • Using ExtJS with ASP.NET, Webforms or MVC?

    - by TigrouMeow
    Hello, For a scenario using 0 ASP.NET controls at all but rather an 100% extJS interface, what would be the advantages of using ASP.NET MVC or ASP.NET WebForms? And the disadvantages? Is there a OBVIOUS way to do it properly? I would love to have feedback's on your experiences. Thank you!

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  • Recommend ASP.NET 3.5 SP1 Hosting Providers

    - by tyndall
    Would like to see a list of affordable ASP.NET 3.5 SP1 Hosting providers build up. Along with your review of the service, lacking features, special features, etc... Discount ASP.NET MochaHost At last update MochaHost does not offer SP1  they now offer SP1 CrystalTech Gearhost HostMySite please add more update: Anybody see a better deal for shared hosting ASP.NET than ASP.NETpro From GearHost? I would like to see more SQL storage, but I need keep the multiple domain capabilities. For about the same price.

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  • Linq To Sql or classic ADO.net?

    - by Spyros
    I am asking my self many times before start writting a new app or data access library , should I use LinqToSql or classic ADO.net , I have used both and the development time I spend on building an app with Linq To sql is like the 1/3 compared to ADO.net. The only think I like using Linq to sql is that I dont have to design the domain objects Linq does that for me and saves me from spend my time on boring things :P But is Linq to sql suitable for large scale projects , is there an overhead that we can avoid when using ADO.net ?

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  • asp.net application install folder

    - by Maximilian Csuk
    Disclaimer: this is not a question about how to install asp.net or an application using it! Hi! I am pretty sure many of you have once installed some kind of forum, blog or CMS (mostly PHP powered applications). All of these contain a folder mostly named "install" where (after you copied the files to the webserver) point your browser to to complete the installation by entering for example database information (servername, username, password, ...). After that, most applications suggest that you delete this folder or at least change the permissions so nobody from the outside can access it anymore. Now to my question: how would you go about that in the asp.net world? I don't really like the "install folder"-approach and I thought there might be a different mechanism for .net/IIS. The person installing my application should be able to enter his database information as painless as possible, which should ultimatively be stored in the web.config file. If it makes a difference, I am using asp.net MVC. Thanks for your help!

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  • Membership with Mysql, EF 1 and ASP.NET 3.5

    - by sanfra1983
    Hi, I created a web application with asp.net 3.5 and ado.net entity framework WebForms 1, but have not yet succeeded in creating a memebrship and roles. When I go on ASP.NET Configuration and click the Security Tab I get the following error: Keyword not supported. Parameter name: metadata Someone has already created an application with these same features to help me understand where is the problem? P.S.: I'm going crazy Thanks to all

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  • TCP Zero Window with no corresponding Window Update

    - by Gandalf
    I am trying to debug a network issue and am using Wireshark and tcpdump to grab packets from my server. I have one client application that is grabbing all my available connections and then holding them, trying to send A LOT of data and essentially causing an unintentional DOS attack. While debugging I notice that I see my server sending "Window Closed" and "Zero Window" TCP packets - but never sending any "Window Update" packets. I am guessing this is why the client never lets go of the connections (it still has more data to send and is waiting). Has anyone ever seen this type of behavior before? Let's not get into the reasons why I haven't set up an iptables rule to limit concurrent connections (yeah I know). I also recently changed the MTU from 1500 to 9000 - could this have such a negative effect? (Linux) Thanks.

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  • Duplicate incoming TCP traffic on Debian Squeeze

    - by Erwan Queffélec
    I have to test a homebrew server that accepts a lot of incoming TCP traffic on a single port. The protocol is homebrew as well. For testing purposes, I'd like to send this traffic both : - to the production server (say, listening on port 12345) - to the test server (say, listening on port 23456) My clients apps are "dumb" : they never read data back, and the server never replies anyway, my server only accepts connections, and do statistical computations and store/forward/service both raw and computed data. Actually, client apps and hardware are so simple there is no way I can tell clients to send their stream on both servers... And using "fake" clients is not good enough. What could be the simplest solution ? I can of course write an intermediary app that just copy incoming data and send it back to the testing server, pretending to be the client. I have a single server running Squeeze and have total control over it. Thanks in advance for your replies.

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  • AIX network parameters to close TCP sockets of unplugged devices

    - by ADD Geek
    Hi there We have an AIX box, running what we call in banking "ATM Switch" not the ATM networking switch, but the bank ATM driver. where we have some ATM machines connected to two server processes. The problem is, when we disconnect any of these machines, the netstat -na| grep <port number> command shows that the socket established for this disconnected device is still established, we have to manually send a command from the software to make the socket aware that it is not live anymore. Is there a parameter on tcp level to make this connection aware within a minute or two that this device is not connected anymore? we had the following parameters set with root privileges: no -o tcp_keepidle=1000 no -o tcp_keepcnt=2 no -o tcp_keepintvl=150 no -o tcp_finwait2=100 it was originally having the default values. but even after we changed these parameters and restarted the server processes, the problem was still there.

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  • TCP failure on Solaris

    - by anurag kohli
    Hi All, I recently ran into a problem where a Solaris server could not establish a TCP socket on port 2126. From a packet capture I see this (note: A is a Solaris server, B is a router): A sends SYN to B B sends SYN, ACK to A Notice A (Solaris) does not acknowledge the SYN from B. Due to the business impact of the problem, I had to reboot the server to fix the problem. That said, I want to know the next time the problem occurs, what can I do to get a root cause (ie before server reboot)? Thanks in advance.

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  • Several Server Errors (No database connect, can't create TCP/IP socket etc

    - by Tobias Baumeister
    My server stops taking requests on my website today. It works for some time, but then the server just stops working and throws several errors: 500 Internal Server Error Warning: mysql_connect(): Can't create TCP/IP socket (105) in [...] on line 7 Couldn't connect to database. Please try again. mysql_connect(): Host [...] is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts' mod_fcgid: can't apply process slot for /var/www/cgi-bin/cgi_wrapper/cgi_wrapper (this is from Error Log) Any ideas what might cause it? operating system is Ubuntu

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  • How to config DNS onto TCP from UDP

    - by Dante Jiang
    Google DNS (8.8.8.8 and 8.8.4.4) are blocked (or polluted) by all ISPs available to me (and DNS by ISPs just return wrong answers for some sensitive sites!!), and it is said that if we change DNS from UDP onto TCP, the problem can be temporarily solved. My question is: how to config that on Windows 7? The solution provided by the original post: Windows 7 Ultimate DnsApi.dll v6.1.7601.17570 .text:6DC08FC8 8B 46 10 mov eax, [esi+10h] .text:6DC08FCB 89 45 F4 mov [ebp+var_C], eax var_C - 2 85A0: 90 90 90 90 90 -> 33 C0 40 EB 25 85C8: 8B 46 10 -> EB D6 40 I have not figure out how the original solution works so far. It needs to modify the .dll file, and the post provides a .dll after modification. However, I wish there was a solution without this kind of hacking.

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  • Which TCP ports to use?

    - by rowatt
    Is there a TCP port range which I can be sure will not be used by anything else for traffic between two machines? If I am reading RFC6335 correctly, I can be sure that no other applications will use specific ports in the Dynamic/Private/Ephemeral range of 49152-65535. However, if I understand correctly, it also states (section 8.1.2) that an application shouldn't assume that any given port in that range is available at any given time, which would mean I can't be 100% sure that it will be unused all the time. Specifically, I want to assign specific SSH traffic to a different port for the security benefit and so I can classify it differently for QoS purposes, and not have to worry about changing the port in the future.

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  • TCP handshake ok, then the client isn't receiving any packets from the server

    - by infgeoax
    Topology: Client ----- Intermediate Device ----- Server Client: win7 Intermediate Device: unknown Server: CentOS 5.8 The problem occurs when the client and server are trying to establish a SSL connection. It happens to one specific port, 2000. I haven't been able to replicate the problem with other port numbers. I captured packets on both client and server. After the TCP handshake, from the client's perspective, it's not receiving ACKs for its previously sent packets so it kept re-sending them. On the server side, however, it did receive those packets and sent ACK packets. The weird thing is, after the server sent those ACKs, it received a [RST, ACK] packet, from the intermediate device, for every packet it sent. What could be the cause?

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  • Using ASP.NET C# and Javascript

    - by ctck
    I'm looking for the most efficient / standardized way of passing data between client javascript code and C# code behind in an ASP.NET application. Currently ive been using the following methods to achieve this but they all feel a bit like a fudge. The way i pass data from javascript to the C# code behind is by setting hidden asp variables and triggering a postback <asp:HiddenField ID="RandomList" runat="server" /> function SetDataField(data) { document.getElementById('<%=RandomList.ClientID%>').value = data; } Then in C# code i collect the list protected void GetData(object sender, EventArgs e) { var _list = RandomList.value; } Going back the other way i often use either scriptmanager to register a function and pass it data during Page_Load: ScriptManager.RegisterStartupScript(this.GetType(), "Set","get("Test();",true); or i add attributes to controls before a post back or during Initialization / pre rendering stages: Btn.Attributes.Add("onclick", "DisplayMessage("Hello");"); These methods have served me well and do the job. However they just dont feel complete. Is there a more standardized way of passing data between client side markup / javascript and backend code. Ive seen some posts like this one: Injecting JavaScrip : StackOverflow that describe HtmlElement class. Is this something is should look into? Thanks everyone for your time.

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  • ASP.NET ViewState Tips and Tricks #2

    - by João Angelo
    If you need to store complex types in ViewState DO implement IStateManager to control view state persistence and reduce its size. By default a serializable object will be fully stored in view state using BinaryFormatter. A quick comparison for a complex type with two integers and one string property produces the following results measured using ASP.NET tracing: BinaryFormatter: 328 bytes in view state IStateManager: 28 bytes in view state BinaryFormatter sample code: // DO NOT [Serializable] public class Info { public int Id { get; set; } public string Name { get; set; } public int Age { get; set; } } public class ExampleControl : WebControl { protected override void OnLoad(EventArgs e) { base.OnLoad(e); if (!this.Page.IsPostBack) { this.User = new Info { Id = 1, Name = "John Doe", Age = 27 }; } } public Info User { get { object o = this.ViewState["Example_User"]; if (o == null) return null; return (Info)o; } set { this.ViewState["Example_User"] = value; } } } IStateManager sample code: // DO public class Info : IStateManager { public int Id { get; set; } public string Name { get; set; } public int Age { get; set; } private bool isTrackingViewState; bool IStateManager.IsTrackingViewState { get { return this.isTrackingViewState; } } void IStateManager.LoadViewState(object state) { var triplet = (Triplet)state; this.Id = (int)triplet.First; this.Name = (string)triplet.Second; this.Age = (int)triplet.Third; } object IStateManager.SaveViewState() { return new Triplet(this.Id, this.Name, this.Age); } void IStateManager.TrackViewState() { this.isTrackingViewState = true; } } public class ExampleControl : WebControl { protected override void OnLoad(EventArgs e) { base.OnLoad(e); if (!this.Page.IsPostBack) { this.User = new Info { Id = 1, Name = "John Doe", Age = 27 }; } } public Info User { get; set; } protected override object SaveViewState() { return new Pair( ((IStateManager)this.User).SaveViewState(), base.SaveViewState()); } protected override void LoadViewState(object savedState) { if (savedState != null) { var pair = (Pair)savedState; this.User = new Info(); ((IStateManager)this.User).LoadViewState(pair.First); base.LoadViewState(pair.Second); } } }

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  • Employee Info Starter Kit - Visual Studio 2010 and .NET 4.0 Version (4.0.0) Available

    - by Mohammad Ashraful Alam
    Employee Info Starter Kit is a ASP.NET based web application, which includes very simple user requirements, where we can create, read, update and delete (crud) the employee info of a company. Based on just a database table, it explores and solves most of the major problems in web development architectural space.  This open source starter kit extensively uses major features available in latest Visual Studio, ASP.NET and Sql Server to make robust, scalable, secured and maintanable web applications quickly and easily. Since it's first release, this starter kit achieved a huge popularity in web developer community and includes 1,40,000+ download from project web site. Visual Studio 2010 and .NET 4.0 came up with lots of exciting features to make software developers life easier.  A new version (v4.0.0) of Employee Info Starter Kit is now available in both MSDN Code Gallery and CodePlex. Chckout the latest version of this starter kit to enjoy cool features available in Visual Studio 2010 and .NET 4.0. [ Release Notes ] Architectural Overview Simple 2 layer architecture (user interface and data access layer) with 1 optional cache layer ASP.NET Web Form based user interface Custom Entity Data Container implemented (with primitive C# types for data fields) Active Record Design Pattern based Data Access Layer, implemented in C# and Entity Framework 4.0 Sql Server Stored Procedure to perform actual CRUD operation Standard infrastructure (architecture, helper utility) for automated integration (bottom up manner) and unit testing Technology UtilizedProgramming Languages/Scripts Browser side: JavaScript Web server side: C# 4.0 Database server side: T-SQL .NET Framework Components .NET 4.0 Entity Framework .NET 4.0 Optional/Named Parameters .NET 4.0 Tuple .NET 3.0+ Extension Method .NET 3.0+ Lambda Expressions .NET 3.0+ Aanonymous Type .NET 3.0+ Query Expressions .NET 3.0+ Automatically Implemented Properties .NET 3.0+ LINQ .NET 2.0 + Partial Classes .NET 2.0 + Generic Type .NET 2.0 + Nullable Type   ASP.NET 3.5+ List View (TBD) ASP.NET 3.5+ Data Pager (TBD) ASP.NET 2.0+ Grid View ASP.NET 2.0+ Form View ASP.NET 2.0+ Skin ASP.NET 2.0+ Theme ASP.NET 2.0+ Master Page ASP.NET 2.0+ Object Data Source ASP.NET 1.0+ Role Based Security Visual Studio Features Visual Studio 2010 CodedUI Test Visual Studio 2010 Layer Diagram Visual Studio 2010 Sequence Diagram Visual Studio 2010 Directed Graph Visual Studio 2005+ Database Unit Test Visual Studio 2005+ Unit Test Visual Studio 2005+ Web Test Visual Studio 2005+ Load Test Sql Server Features Sql Server 2005 Stored Procedure Sql Server 2005 Xml type Sql Server 2005 Paging support

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  • Adding page title to each page while creating a PDF file using itextsharp in VB.NET

    - by Snowy
    I have recently started using itextsharp and gradually learning it. So far I created a PDF file and it seems great. I have added a table and some subtables as the first table cells to hold data. It is done using two for loops. The first one loops through all data and the second one is each individual data displayed in columns. The html outcome looks like the following: <table> <tr> <td>Page title in center</td> </tr> <tr> <td> <table> <tr> <td>FirstPersonName</td> <td>Rank1</td> <td>info1a</td> <td>infob</td> <td>infoc</td> </tr> </table> </td> <td> <table> <tr> <td>SecondPersonName</td> <td>Rank2</td> <td>info1a</td> <td>infob</td> <td>infoc</td> <td>infod</td> <td>infoe</td> </tr> </table> </td> <td> <table> <tr> <td>ThirdPersonName</td> <td>Rank2</td> <td>info1a</td> <td>infob</td> <td>infoc</td> <td>infod</td> <td>infoe</td> <td>infof</td> <td>infog</td> </tr> </table> </td> </tr> </table> For page headings, I added a cell at the top before any other cells. I need to add this heading to all pages. Depending on the size of data, some pages have two rows and some pages have three rows of data. So I can not tell exactly when the new page starts to add the heading/title. My question is how to add the heading/title to all pages. I use VB.net. I searched for answer online and had no success. Your help would be greatly appreciated.

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  • Issues integrating NCover with CC.NET, .NET framework 4.0 and MsTest

    - by Nikhil
    I'm implementing continuous integration with CruiseControl.NET, .NET 4.0, NCover and MsTest. On the build server I'm unable to run code coverage from the Ncover explorer or NCover console. When I run where vstesthost.exe from the Ncover console it returns the Visual Studio 9.0 path and does not seem to pick up .net framework 4.0. I've followed instructions from this MSTest: Measuring Test Quality With NCover post with slight modifications for .net framework 4.0, without any success. My CC.NET script looks like this <exec> <executable>C:\Program Files (x86)\NCover\NCover.Console.exe</executable> <baseDirectory>$(project_root)\</baseDirectory> <buildArgs>"C:\Program Files (x86)\**Microsoft Visual Studio 10.0**\Common7\IDE\MSTest.exe" /testcontainer:...\...\UnitTests.dll /resultsfile:TestResults.trx //xml D:\_Projects\....\Temp_Coverage.xml //pm vstesthost.exe</buildArgs> <buildTimeoutSeconds>$(ncover.timeout)</buildTimeoutSeconds> </exec> Has anyone come across similar issue. Any help would be much appreciated.

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  • Parallelism in .NET – Part 16, Creating Tasks via a TaskFactory

    - by Reed
    The Task class in the Task Parallel Library supplies a large set of features.  However, when creating the task, and assigning it to a TaskScheduler, and starting the Task, there are quite a few steps involved.  This gets even more cumbersome when multiple tasks are involved.  Each task must be constructed, duplicating any options required, then started individually, potentially on a specific scheduler.  At first glance, this makes the new Task class seem like more work than ThreadPool.QueueUserWorkItem in .NET 3.5. In order to simplify this process, and make Tasks simple to use in simple cases, without sacrificing their power and flexibility, the Task Parallel Library added a new class: TaskFactory. The TaskFactory class is intended to “Provide support for creating and scheduling Task objects.”  Its entire purpose is to simplify development when working with Task instances.  The Task class provides access to the default TaskFactory via the Task.Factory static property.  By default, TaskFactory uses the default TaskScheduler to schedule tasks on a ThreadPool thread.  By using Task.Factory, we can automatically create and start a task in a single “fire and forget” manner, similar to how we did with ThreadPool.QueueUserWorkItem: Task.Factory.StartNew(() => this.ExecuteBackgroundWork(myData) ); .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 us with the same level of simplicity we had with ThreadPool.QueueUserWorkItem, but even more power.  For example, we can now easily wait on the task: // Start our task on a background thread var task = Task.Factory.StartNew(() => this.ExecuteBackgroundWork(myData) ); // Do other work on the main thread, // while the task above executes in the background this.ExecuteWorkSynchronously(); // Wait for the background task to finish task.Wait(); TaskFactory simplifies creation and startup of simple background tasks dramatically. In addition to using the default TaskFactory, it’s often useful to construct a custom TaskFactory.  The TaskFactory class includes an entire set of constructors which allow you to specify the default configuration for every Task instance created by that factory.  This is particularly useful when using a custom TaskScheduler.  For example, look at the sample code for starting a task on the UI thread in Part 15: // Given the following, constructed on the UI thread // TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); // When inside a background task, we can do string status = GetUpdatedStatus(); (new Task(() => { statusLabel.Text = status; })) .Start(uiScheduler); This is actually quite a bit more complicated than necessary.  When we create the uiScheduler instance, we can use that to construct a TaskFactory that will automatically schedule tasks on the UI thread.  To do that, we’d create the following on our main thread, prior to constructing our background tasks: // Construct a task scheduler from the current SynchronizationContext (UI thread) var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); // Construct a new TaskFactory using our UI scheduler var uiTaskFactory = new TaskFactory(uiScheduler); If we do this, when we’re on a background thread, we can use this new TaskFactory to marshal a Task back onto the UI thread.  Our previous code simplifies to: // When inside a background task, we can do string status = GetUpdatedStatus(); // Update our UI uiTaskFactory.StartNew( () => statusLabel.Text = status); Notice how much simpler this becomes!  By taking advantage of the convenience provided by a custom TaskFactory, we can now marshal to set data on the UI thread in a single, clear line of code!

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  • Parallelism in .NET – Part 8, PLINQ’s ForAll Method

    - by Reed
    Parallel LINQ extends LINQ to Objects, and is typically very similar.  However, as I previously discussed, there are some differences.  Although the standard way to handle simple Data Parellelism is via Parallel.ForEach, it’s possible to do the same thing via PLINQ. PLINQ adds a new method unavailable in standard LINQ which provides new functionality… LINQ is designed to provide a much simpler way of handling querying, including filtering, ordering, grouping, and many other benefits.  Reading the description in LINQ to Objects on MSDN, it becomes clear that the thinking behind LINQ deals with retrieval of data.  LINQ works by adding a functional programming style on top of .NET, allowing us to express filters in terms of predicate functions, for example. PLINQ is, generally, very similar.  Typically, when using PLINQ, we write declarative statements to filter a dataset or perform an aggregation.  However, PLINQ adds one new method, which provides a very different purpose: ForAll. The ForAll method is defined on ParallelEnumerable, and will work upon any ParallelQuery<T>.  Unlike the sequence operators in LINQ and PLINQ, ForAll is intended to cause side effects.  It does not filter a collection, but rather invokes an action on each element of the collection. At first glance, this seems like a bad idea.  For example, Eric Lippert clearly explained two philosophical objections to providing an IEnumerable<T>.ForEach extension method, one of which still applies when parallelized.  The sole purpose of this method is to cause side effects, and as such, I agree that the ForAll method “violates the functional programming principles that all the other sequence operators are based upon”, in exactly the same manner an IEnumerable<T>.ForEach extension method would violate these principles.  Eric Lippert’s second reason for disliking a ForEach extension method does not necessarily apply to ForAll – replacing ForAll with a call to Parallel.ForEach has the same closure semantics, so there is no loss there. Although ForAll may have philosophical issues, there is a pragmatic reason to include this method.  Without ForAll, we would take a fairly serious performance hit in many situations.  Often, we need to perform some filtering or grouping, then perform an action using the results of our filter.  Using a standard foreach statement to perform our action would avoid this philosophical issue: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action foreach (var item in filteredItems) { // These will now run serially item.DoSomething(); } .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 would cause a loss in performance, since we lose any parallelism in place, and cause all of our actions to be run serially. We could easily use a Parallel.ForEach instead, which adds parallelism to the actions: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action once the filter completes Parallel.ForEach(filteredItems, item => { // These will now run in parallel item.DoSomething(); }); This is a noticeable improvement, since both our filtering and our actions run parallelized.  However, there is still a large bottleneck in place here.  The problem lies with my comment “perform an action once the filter completes”.  Here, we’re parallelizing the filter, then collecting all of the results, blocking until the filter completes.  Once the filtering of every element is completed, we then repartition the results of the filter, reschedule into multiple threads, and perform the action on each element.  By moving this into two separate statements, we potentially double our parallelization overhead, since we’re forcing the work to be partitioned and scheduled twice as many times. This is where the pragmatism comes into play.  By violating our functional principles, we gain the ability to avoid the overhead and cost of rescheduling the work: // Perform an action on the results of our filter collection .AsParallel() .Where( i => i.SomePredicate() ) .ForAll( i => i.DoSomething() ); The ability to avoid the scheduling overhead is a compelling reason to use ForAll.  This really goes back to one of the key points I discussed in data parallelism: Partition your problem in a way to place the most work possible into each task.  Here, this means leaving the statement attached to the expression, even though it causes side effects and is not standard usage for LINQ. This leads to my one guideline for using ForAll: The ForAll extension method should only be used to process the results of a parallel query, as returned by a PLINQ expression. Any other usage scenario should use Parallel.ForEach, instead.

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  • Parallelism in .NET – Part 17, Think Continuations, not Callbacks

    - by Reed
    In traditional asynchronous programming, we’d often use a callback to handle notification of a background task’s completion.  The Task class in the Task Parallel Library introduces a cleaner alternative to the traditional callback: continuation tasks. Asynchronous programming methods typically required callback functions.  For example, MSDN’s Asynchronous Delegates Programming Sample shows a class that factorizes a number.  The original method in the example has the following signature: public static bool Factorize(int number, ref int primefactor1, ref int primefactor2) { //... .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; } However, calling this is quite “tricky”, even if we modernize the sample to use lambda expressions via C# 3.0.  Normally, we could call this method like so: int primeFactor1 = 0; int primeFactor2 = 0; bool answer = Factorize(10298312, ref primeFactor1, ref primeFactor2); Console.WriteLine("{0}/{1} [Succeeded {2}]", primeFactor1, primeFactor2, answer); If we want to make this operation run in the background, and report to the console via a callback, things get tricker.  First, we need a delegate definition: public delegate bool AsyncFactorCaller( int number, ref int primefactor1, ref int primefactor2); Then we need to use BeginInvoke to run this method asynchronously: int primeFactor1 = 0; int primeFactor2 = 0; AsyncFactorCaller caller = new AsyncFactorCaller(Factorize); caller.BeginInvoke(10298312, ref primeFactor1, ref primeFactor2, result => { int factor1 = 0; int factor2 = 0; bool answer = caller.EndInvoke(ref factor1, ref factor2, result); Console.WriteLine("{0}/{1} [Succeeded {2}]", factor1, factor2, answer); }, null); This works, but is quite difficult to understand from a conceptual standpoint.  To combat this, the framework added the Event-based Asynchronous Pattern, but it isn’t much easier to understand or author. Using .NET 4’s new Task<T> class and a continuation, we can dramatically simplify the implementation of the above code, as well as make it much more understandable.  We do this via the Task.ContinueWith method.  This method will schedule a new Task upon completion of the original task, and provide the original Task (including its Result if it’s a Task<T>) as an argument.  Using Task, we can eliminate the delegate, and rewrite this code like so: var background = Task.Factory.StartNew( () => { int primeFactor1 = 0; int primeFactor2 = 0; bool result = Factorize(10298312, ref primeFactor1, ref primeFactor2); return new { Result = result, Factor1 = primeFactor1, Factor2 = primeFactor2 }; }); background.ContinueWith(task => Console.WriteLine("{0}/{1} [Succeeded {2}]", task.Result.Factor1, task.Result.Factor2, task.Result.Result)); This is much simpler to understand, in my opinion.  Here, we’re explicitly asking to start a new task, then continue the task with a resulting task.  In our case, our method used ref parameters (this was from the MSDN Sample), so there is a little bit of extra boiler plate involved, but the code is at least easy to understand. That being said, this isn’t dramatically shorter when compared with our C# 3 port of the MSDN code above.  However, if we were to extend our requirements a bit, we can start to see more advantages to the Task based approach.  For example, supposed we need to report the results in a user interface control instead of reporting it to the Console.  This would be a common operation, but now, we have to think about marshaling our calls back to the user interface.  This is probably going to require calling Control.Invoke or Dispatcher.Invoke within our callback, forcing us to specify a delegate within the delegate.  The maintainability and ease of understanding drops.  However, just as a standard Task can be created with a TaskScheduler that uses the UI synchronization context, so too can we continue a task with a specific context.  There are Task.ContinueWith method overloads which allow you to provide a TaskScheduler.  This means you can schedule the continuation to run on the UI thread, by simply doing: Task.Factory.StartNew( () => { int primeFactor1 = 0; int primeFactor2 = 0; bool result = Factorize(10298312, ref primeFactor1, ref primeFactor2); return new { Result = result, Factor1 = primeFactor1, Factor2 = primeFactor2 }; }).ContinueWith(task => textBox1.Text = string.Format("{0}/{1} [Succeeded {2}]", task.Result.Factor1, task.Result.Factor2, task.Result.Result), TaskScheduler.FromCurrentSynchronizationContext()); This is far more understandable than the alternative.  By using Task.ContinueWith in conjunction with TaskScheduler.FromCurrentSynchronizationContext(), we get a simple way to push any work onto a background thread, and update the user interface on the proper UI thread.  This technique works with Windows Presentation Foundation as well as Windows Forms, with no change in methodology.

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