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  • ResolveUrl() from WCF service

    - by Michael Freidgeim
    I wanted to ResolveUrl() from WCF service and foundhttp://www.west-wind.com/weblog/posts/2007/Sep/18/ResolveUrl-without-Page .However the function assumes that the call is synchronous, in asynchronous call (e.g called from TPL task) HttpContext.Current==null.I had to split my asynchronous method into two-a long asynchronous one, invoked as task and generating relative URL and a post-task, that is calling wwWebUtils.ResolveServerUrl(relativeUrL)The http://www.codeproject.com/Articles/205425/ASP-NET-ResolveUrl-Without-Page  article suggests to useSystem.Web.VirtualPathUtility.ToAbsolute("~/default.aspx");but i expect, it wouldn’t work from asynchronous thread as well.

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  • Slides and Code from “Using C#’s Async Effectively”

    - by Reed
    The slides and code from my talk on the new async language features in C# and VB.Net are now available on https://github.com/ReedCopsey/Effective-Async This includes the complete slide deck, and all 4 projects, including: FakeService: Simple WCF service to run locally and simulate network service calls. AsyncService: Simple WCF service which wraps FakeService to demonstrate converting sync to async SimpleWPFExample: Simplest example of converting a method call to async from a synchronous version AsyncExamples: Windows Store application demonstrating main concepts, pitfalls, tips, and tricks from the slide deck

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  • LOB Pointer Indexing Proposal

    - by jchang
    My observations are that IO to lob pages (and row overflow pages as well?) is restricted to synchronous IO, which can result in serious problems when these reside on disk drive storage. Even if the storage system is comprised of hundreds of HDDs, the realizable IO performance to lob pages is that of a single disk, with some improvement in parallel execution plans. The reason for this appears to be that each thread must work its way through a page to find the lob pointer information, and then generates...(read more)

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  • Occasional disk I/O errors in SQLite

    - by Alix Axel
    I have a very simple website running PHP and SQLite 3.7.9 (with PDO). After establishing the SQLite connection I immediately execute the following queries: PRAGMA busy_timeout=0; PRAGMA cache_size=8192; PRAGMA foreign_keys=ON; PRAGMA journal_size_limit=67110000; PRAGMA legacy_file_format=OFF; PRAGMA page_size=4096; PRAGMA recursive_triggers=ON; PRAGMA secure_delete=ON; PRAGMA synchronous=NORMAL; PRAGMA temp_store=MEMORY; PRAGMA journal_mode=WAL; PRAGMA wal_autocheckpoint=4096; This website only has one writer and a few occasional readers, so I don't expect any concurrency problems (and I'm even using WAL). Every couple of days, I've seen this error being reported by PHP: Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 10 disk I/O error' in ... Stack trace: #0 ...: PDO-exec('PRAGMA cache_si...') There are several things that make this error very weird to me: it's not a transient problem - no matter how many times I refresh the page, it won't go away the database file is not corrupted - the sqlite3 executable can open the database without problems If the following pragmas are commented out, PHP stops throwing the disk I/O exception: PRAGMA cache_size=8192; PRAGMA synchronous=NORMAL; PRAGMA journal_mode=WAL; Then, after successfully reconnecting to the database, I'm able to reintroduce these pragmas and the code with run smoothly for days - until eventually, the same error will occur without any apparent reason. I wasn't able to reproduce this error so far, so I'm clueless about the origin of it. I'm really curious what may be causing this problem... Any ideas? Environment: Ubuntu Server 12.04 LTS PHP 5.4.15 SQLite 3.7.9 Database size: ? 10MiB Transaction (write) size: ? 1KiB EDIT: Might these symptoms have something to do with busy_timeout?

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  • RAM being displayed is lesser than the actual in my Windows 7

    - by Prateek Somani
    I am using Windows 7 and Ubuntu on the same machine. Earlier I had 3 GB of RAM,but now the Windows is displaying just 1 GB of RAM. Please also find the output of the free command in my Ubuntu : total used free shared buffers cached Mem: 1008208 904808 103400 5736 13516 239596 -/+ buffers/cache: 651696 356512 Swap: 3127292 10252 3117040 Has the swap memory consumed my 2 GB of RAM? Will I be able to use the whole of 3GB of the RAM in my Windows? Regards, Prateek Update : I tried to run the lshw command and I got the following output : *-memory description: System Memory physical id: 1b slot: System board or motherboard size: 1GiB *-bank:0 description: SODIMM DDR3 Synchronous 1067 MHz (0.9 ns) product: HMT112S6BFR6C-H9 vendor: Hynix physical id: 0 serial: 2C71D069 slot: Bottom - Slot 1 size: 1GiB width: 64 bits clock: 1067MHz (0.9ns) *-bank:1 description: SODIMM DDR3 Synchronous 1067 MHz (0.9 ns) [empty] product: 16JSF25664HZ-1G4F1 vendor: Micron physical id: 1 serial: FD421821 slot: Bottom - Slot 2 width: 64 bits clock: 1067MHz (0.9ns) Why it is able to detect the vendor/product name of the bank-1 RAM, why can't it detect the RAM size and other details ? Has my RAM got faulty?

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  • Distributed storage and computing

    - by Tim van Elteren
    Dear Serverfault community, After researching a number of distributed file systems for deployment in a production environment with the main purpose of performing both batch and real-time distributed computing I've identified the following list as potential candidates, mainly on maturity, license and support: Ceph Lustre GlusterFS HDFS FhGFS MooseFS XtreemFS The key properties that our system should exhibit: an open source, liberally licensed, yet production ready, e.g. a mature, reliable, community and commercially supported solution; ability to run on commodity hardware, preferably be designed for it; provide high availability of the data with the most focus on reads; high scalability, so operation over multiple data centres, possibly on a global scale; removal of single points of failure with the use of replication and distribution of (meta-)data, e.g. provide fault-tolerance. The sensitivity points that were identified, and resulted in the following questions, are: transparency to the processing layer / application with respect to data locality, e.g. know where data is physically located on a server level, mainly for resource allocation and fast processing, high performance, how can this be accomplished? Do you from experience know what solutions provide this transparency and to what extent? posix compliance, or conformance, is mentioned on the wiki pages of most of the above listed solutions. The question here mainly is, how relevant is support for the posix standard? Hadoop for example isn't posix compliant by design, what are the pro's and con's? what about the difference between synchronous and asynchronous opeartion of a distributed file system. Though a synchronous distributed file system has the preference because of reliability it also imposes certain limitations with respect to scalability. What would be, from your expertise, the way to go on this? I'm looking forward to your replies. Thanks in advance! :) With kind regards, Tim van Elteren

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  • Can't connect to VPN on Ubuntu 12.04

    - by 12rad
    I'm having a lot of trouble connecting to VPN. This used to work on my machine, but i recently did an update and it's stopped working. I'm not sure what the problem is. My question is how do i debug this? I'm not able to narrow it down to a specific problem. This is what i get when i tail the syslogs. Would appreciate any help! Nov 6 23:42:52 meera NetworkManager[1137]: <info> Starting VPN service 'pptp'... Nov 6 23:42:52 meera NetworkManager[1137]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 6132 Nov 6 23:42:52 meera NetworkManager[1137]: <info> VPN service 'pptp' appeared; activating connections Nov 6 23:42:52 meera NetworkManager[1137]: <info> VPN plugin state changed: starting (3) Nov 6 23:42:52 meera NetworkManager[1137]: <info> VPN connection 'NAME VPN' (Connect) reply received. Nov 6 23:42:52 meera pppd[6136]: Plugin /usr/lib/pppd/2.4.5/nm-pptp-pppd-plugin.so loaded. Nov 6 23:42:52 meera pppd[6136]: pppd 2.4.5 started by root, uid 0 Nov 6 23:42:52 meera chat[6139]: timeout set to 15 seconds Nov 6 23:42:52 meera chat[6139]: abort on (NO CARRIER) Nov 6 23:42:52 meera chat[6139]: abort on (NO DIALTONE) Nov 6 23:42:52 meera chat[6139]: abort on (ERROR) Nov 6 23:42:52 meera chat[6139]: abort on (NO ANSWER) Nov 6 23:42:52 meera chat[6139]: abort on (BUSY) Nov 6 23:42:52 meera chat[6139]: abort on (Username/Password Incorrect) Nov 6 23:42:52 meera chat[6139]: send (AT^M) Nov 6 23:42:52 meera pptp[6138]: nm-pptp-service-6132 log[main:pptp.c:314]: The synchronous pptp option is NOT activated Nov 6 23:42:52 meera chat[6139]: expect (OK) Nov 6 23:42:52 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request' Nov 6 23:42:53 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply Nov 6 23:42:53 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established. Nov 6 23:42:53 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request' Nov 6 23:42:54 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply. Nov 6 23:42:54 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 13077). Nov 6 23:42:54 meera pptp[6138]: nm-pptp-service-6132 warn[decaps_hdlc:pptp_gre.c:231]: The ppp mode is synchronous, yet no pptp --sync option is specified! Nov 6 23:43:07 meera chat[6139]: alarm Nov 6 23:43:07 meera chat[6139]: Failed Nov 6 23:43:07 meera pppd[6136]: Script chat -v -f /etc/ppp/chat-ztisp finished (pid 6139), status = 0x3 Nov 6 23:43:07 meera pppd[6136]: Connect script failed Nov 6 23:43:07 meera pppd[6136]: Waiting for 1 child processes... Nov 6 23:43:07 meera pppd[6136]: script /usr/sbin/pptp 204.197.218.90 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-6132, pid 6138 Nov 6 23:43:07 meera pptp[6138]: nm-pptp-service-6132 warn[decaps_hdlc:pptp_gre.c:204]: short read (-1): Input/output error Nov 6 23:43:07 meera pptp[6138]: nm-pptp-service-6132 warn[decaps_hdlc:pptp_gre.c:216]: pppd may have shutdown, see pppd log Nov 6 23:43:07 meera pptp[6143]: nm-pptp-service-6132 log[callmgr_main:pptp_callmgr.c:234]: Closing connection (unhandled) Nov 6 23:43:07 meera pppd[6136]: Script /usr/sbin/pptp 204.197.218.90 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-6132 finished (pid 6138), status = 0x0 Nov 6 23:43:07 meera pptp[6143]: nm-pptp-service-6132 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 12 'Call-Clear-Request' Nov 6 23:43:07 meera pptp[6143]: nm-pptp-service-6132 log[call_callback:pptp_callmgr.c:79]: Closing connection (call state) Nov 6 23:43:07 meera pppd[6136]: Exit. Nov 6 23:43:07 meera NetworkManager[1137]: <warn> VPN plugin failed: 1 Nov 6 23:43:07 meera NetworkManager[1137]: <info> VPN plugin state changed: stopped (6) Nov 6 23:43:07 meera NetworkManager[1137]: <info> VPN plugin state change reason: 0 Nov 6 23:43:07 meera NetworkManager[1137]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.

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  • Running and managing NSTimer in different NSThread/NSRunLoop

    - by mips
    I'm writing a Cocoa application, with a GUI designed in Interface Builder. I need to schedule background activity (at regular intervals) without blocking the UI, so I run it in a separate thread, like this: - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { [self performSelectorInBackground:@selector(schedule) withObject:nil]; } - (void) schedule { NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; NSRunLoop* runLoop = [NSRunLoop currentRunLoop]; timer = [[NSTimer scheduledTimerWithTimeInterval:FEED_UPDATE_INTERVAL target:activityObj selector:@selector(run:) userInfo:nil repeats:YES] retain]; [runLoop run]; [pool release]; } I retain the timer, so I can easily invalidate and reschedule. Problem: I must also fire the run: method in response to GUI events, so it is synchronous (i.e. a "perform activity" button). Like this: [timer fire]; I could do this with performSelectorInBackground too, and of course it doesn't block the UI. But this synchronous firings run in another runloop! So I have no guarantee that they won't overlap. How can I queue all of my firings on the same runloop?

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  • Silverlight Async Design Pattern Issue

    - by Mike Mengell
    I'm in the middle of a Silverlight application and I have a function which needs to call a webservice and using the result complete the rest of the function. My issue is that I would have normally done a synchronous web service call got the result and using that carried on with the function. As Silverlight doesn't support synchronous web service calls without additional custom classes to mimic it, I figure it would be best to go with the flow of async rather than fight it. So my question relates around whats the best design pattern for working with async calls in program flow. In the following example I want to use the myFunction TypeId parameter depending on the return value of the web service call. But I don't want to call the web service until this function is called. How can I alter my code design to allow for the async call? string _myPath; bool myFunction(Guid TypeId) { WS_WebService1.WS_WebService1SoapClient proxy = new WS_WebService1.WS_WebService1SoapClient(); proxy.GetPathByTypeIdCompleted += new System.EventHandler<WS_WebService1.GetPathByTypeIdCompleted>(proxy_GetPathByTypeIdCompleted); proxy.GetPathByTypeIdAsync(TypeId); // Get return value if (myPath == "\\Server1") { //Use the TypeId parameter in here } } void proxy_GetPathByTypeIdCompleted(object sender, WS_WebService1.GetPathByTypeIdCompletedEventArgs e) { string server = e.Result.Server; myPath = '\\' + server; } Thanks in advance, Mike

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  • ItemUpdating called twice after ItemAdded in event receiver

    - by Jason
    I've created an event receiver to handle the ItemAdded and ItemUpdating events on a document library in SharePoint 2010. I've encountered a problem where when I add a document to the library (e.g. by saving it back from Word) the ItemAdded method is correctly called however this is then followed by two calls to ItemUpdating. I have removed all code from my handlers to ensure that it's not something I'm doing inside that is causing the problem. They literally look like: public override void ItemUpdating(SPItemEventProperties properties) { } public override void ItemAdded(SPItemEventProperties properties) { } Does anyone have a solution to this issue? Here is my elements.xml file for the event receiver: <Elements xmlns="http://schemas.microsoft.com/sharepoint/"> <Receivers ListTemplateId="101"> <Receiver> <Name>DocumentsEventReceiverItemUpdating</Name> <Type>ItemUpdating</Type> <Assembly>$SharePoint.Project.AssemblyFullName$</Assembly> <Class>My.Namespace.DocumentsEventReceiver</Class> <SequenceNumber>10000</SequenceNumber> <Synchronization>Synchronous</Synchronization> </Receiver> <Receiver> <Name>DocumentsEventReceiverItemAdded</Name> <Type>ItemAdded</Type> <Assembly>$SharePoint.Project.AssemblyFullName$</Assembly> <Class>My.Namespace.DocumentsEventReceiver</Class> <SequenceNumber>10000</SequenceNumber> <Synchronization>Synchronous</Synchronization> </Receiver> </Receivers> </Elements>

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  • Is it possible to wrap an asynchronous event and its callback in a function that returns a boolean?

    - by Rob Flaherty
    I'm trying to write a simple test that creates an image element, checks the image attributes, and then returns true/false. The problem is that using the onload event makes the test asynchronous. On it own this isn't a problem (using a callback as I've done in the code below is easy), but what I can't figure out is how to encapsulate this into a single function that returns a boolean. I've tried various combinations of closures, recursion, and self-executing functions but have had no luck. So my question: am I being dense and overlooking something simple, or is this in fact not possible, because, no matter what, I'm still trying to wrap an asynchronous function in synchronous expectations? Here's the code: var supportsImage = function(callback) { var img = new Image(); img.onload = function() { //Check attributes and pass true or false to callback callback(true); }; img.src = 'data:image/gif;base64,R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs='; }; supportsImage(function(status){ console.log(status); }); To be clear, what I want is to be able to wrap this in something such that it can be used like: if (supportsImage) { //Do some crazy stuff } Thanks! (Btw, I know there are a ton of SO questions regarding confusion about synchronous vs. asynchronous. Apologies if this can be reduced to something previously answered.)

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  • Server.CreateObject Fails when calling .Net object from ASP on 64-bit windows in IIS 32-bit mode

    - by DrFredEdison
    I have a server running Windows 2003 64-bit, that runs IIS in 32-bit mode. I have a COM object that was registered using the following command: C:\WINDOWS\microsoft.net\Framework\v2.0.50727>regasm D:\Path\To\MyDll.dll /tlb:MyTLB.tlb /codebase When I create the object via ASP I get: Server object error 'ASP 0177 : 8000ffff' Server.CreateObject Failed /includes/a_URLFilter.asp, line 19 8000ffff When I create the object in a vbs script and use the 32-bit version of cscript (in \Windows\syswow64) it works fine. I've checked permissions on the DLL, and the IUSR has Read/Execute. Even if I add the IUSR to the Administrators group, I get the same error. This is the log from ProcessMonitor filtering for the path of my dll (annotated with my actions): [Stop IIS] 1:56:30.0891918 PM w3wp.exe 4088 CloseFile D:\Path\To\MyDll.dll SUCCESS [Start IIS] [Refresh ASP page that uses DLL] 1:56:42.7825154 PM w3wp.exe 2196 QueryOpen D:\Path\To\MyDll.dll SUCCESS CreationTime: 8/19/2009 1:11:17 PM, LastAccessTime: 8/19/2009 1:30:26 PM, LastWriteTime: 8/18/2009 12:09:33 PM, ChangeTime: 8/19/2009 1:22:02 PM, AllocationSize: 20,480, EndOfFile: 20,480, FileAttributes: A 1:56:42.7825972 PM w3wp.exe 2196 QueryOpen D:\Path\To\MyDll.dll SUCCESS CreationTime: 8/19/2009 1:11:17 PM, LastAccessTime: 8/19/2009 1:30:26 PM, LastWriteTime: 8/18/2009 12:09:33 PM, ChangeTime: 8/19/2009 1:22:02 PM, AllocationSize: 20,480, EndOfFile: 20,480, FileAttributes: A 1:56:42.7826961 PM w3wp.exe 2196 CreateFile D:\Path\To\MyDll.dll SUCCESS Desired Access: Generic Read, Disposition: Open, Options: Synchronous IO Non-Alert, Non-Directory File, Attributes: N, ShareMode: Read, Delete, AllocationSize: n/a, Impersonating: SERVER2\IUSR_SERVER2, OpenResult: Opened 1:56:42.7827194 PM w3wp.exe 2196 CreateFileMapping D:\Path\To\MyDll.dll SUCCESS SyncType: SyncTypeCreateSection, PageProtection: 1:56:42.7827546 PM w3wp.exe 2196 CreateFileMapping D:\Path\To\MyDll.dll SUCCESS SyncType: SyncTypeOther 1:56:42.7829130 PM w3wp.exe 2196 Load Image D:\Path\To\MyDll.dll SUCCESS Image Base: 0x6350000, Image Size: 0x8000 1:56:42.7830590 PM w3wp.exe 2196 Load Image D:\Path\To\MyDll.dll SUCCESS Image Base: 0x6360000, Image Size: 0x8000 1:56:42.7838855 PM w3wp.exe 2196 CreateFile D:\Webspace\SecurityDll\bin SUCCESS Desired Access: Read Data/List Directory, Synchronize, Disposition: Open, Options: Directory, Synchronous IO Non-Alert, Attributes: n/a, ShareMode: Read, Write, Delete, AllocationSize: n/a, Impersonating: SERVER2\IUSR_SERVER2, OpenResult: Opened 1:56:42.7839081 PM w3wp.exe 2196 QueryDirectory D:\Path\To\MyDll.INI NO SUCH FILE Filter: SecurityDll.INI 1:56:42.7839281 PM w3wp.exe 2196 CloseFile D:\Webspace\SecurityDll\bin SUCCESS [Refresh ASP page that uses DLL] [Refresh ASP page that uses DLL] [Refresh ASP page that uses DLL] This dll works fine on other servers, running 32-bit windows. I can't think of anything else that would make this work. Any suggestions? UPDATE The .dll is not in the GAC, it is compiled as 32-bit, and is Strongly signed.

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  • Windows XP long login (15 minutes +)

    - by Emily Pinkerton
    I'm having a lot of issues with our Windows XP SP3 machines (about 5, but every week another gets on the bandwagon of this issue). They take forever (15 minutes) to apply the user settings once our employee's enter their username and password to login to our domain. It only happens say if a user has reboot the machine and then when they go to log back in then it hangs forever. Reboot and restart are the key words for sure I've noticed with this issue. Here are things I have tested: •Made sure the DNS was set to point to our two servers (Server01 & Server02 are DNS Domain Controllers, 01 is primary and 02 backup). •No major changes have been applied to our network. •All profiles are local, so I have deleted out local profiles that aren't being used on those machines that run slow. •Also I have tried to enable and disable the Enable Fast Login under the local machines GP. It was not configured originally and when I tested both, it made the computer hang on "applying computer settings" for about 15 minutes. When it finally came up to the login screen the it was very quick to login to the domain. However this doesn't fix my issue, and even more frustrating upon setting it back to being not configured it now still takes for forever to apply computer settings. •I enabled the userenv log and here is what I see, but my experience is limited and I'm not sure how to read it exactly. (see below for log, this isn't the whole thing because it's really long) USERENV(2ec.2f0) 10:50:41:843 LoadUserProfile: LoadUserProfileP succeeded USERENV(2ec.2f0) 10:50:41:843 LoadUserProfile: Returning success. Final Information follows: USERENV(2ec.2f0) 10:50:41:843 lpProfileInfo-UserName = USERENV(2ec.2f0) 10:50:41:843 lpProfileInfo-lpProfilePath = < USERENV(2ec.2f0) 10:50:41:843 lpProfileInfo-dwFlags = 0x0 USERENV(2ec.2f0) 10:50:41:843 LoadUserProfile: Returning TRUE. hProfile = <0x818 USERENV(2ec.2f0) 10:50:41:984 IsSyncForegroundPolicyRefresh: Synchronous, Reason:NonCachedCredentials USERENV(2ec.248) 10:50:41:984 IsSyncForegroundPolicyRefresh: Synchronous, Reason:NonCachedCredentials USERENV(3c4.3dc) 10:51:26:166 LibMain: Process Name: C:\WINDOWS\system\wbem\wmiprvse.exe USERENV(2ec.5cc) 11:05:08:741 ProcessGPOs: network name is 192.168.49.0 USERENV(4a8.888) 11:05:08:804 GetProfileType: Profile already loaded. USERENV(4a8.888) 11:05:08:804 LoadProfileInfo: Failed to query central profile with error 2 USERENV(4a8.888) 11:05:08:804 GetProfileType: ProfileFlags is 0 Also this error is in the file quite a lot: USERENV(328.5bc) 11:05:29:733 GetUserDNSDomainName: Failed to impersonate user USERENV(328.834) 11:05:29:733 ImpersonateUser: Failed to impersonate user with 5. I'm really not sure what else to do with my limited experience, but I'm hoping someone can help me. I feel like I'm dealing with an issue way above my level and any knowledge I can gain out of getting this issue fixed would be amazing.

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  • Problem in working with async and await?

    - by Vicky
    I am trying to upload files to Azure Blob Storage and after successful upload adding the filename to a list for my further operation. When i am doing synchronous it works fine but when i am doing async the error occured. Error : Collection was modified; enumeration operation may not execute. foreach(var file in files) { // ..... await blockBlob.UploadFromStreamAsync(fs); listOfMovedLabelFiles.Add(fileName); } if (listOfMovedLabelFiles.Count > 0) // error point { // my code for further operation } Is there any way to wait till all the async operations get completed.

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  • Parallelism in .NET – Part 13, Introducing the Task class

    - by Reed
    Once we’ve used a task-based decomposition to decompose a problem, we need a clean abstraction usable to implement the resulting decomposition.  Given that task decomposition is founded upon defining discrete tasks, .NET 4 has introduced a new API for dealing with task related issues, the aptly named Task class. The Task class is a wrapper for a delegate representing a single, discrete task within your decomposition.  We will go into various methods of construction for tasks later, but, when reduced to its fundamentals, an instance of a Task is nothing more than a wrapper around a delegate with some utility functionality added.  In order to fully understand the Task class within the new Task Parallel Library, it is important to realize that a task really is just a delegate – nothing more.  In particular, note that I never mentioned threading or parallelism in my description of a Task.  Although the Task class exists in the new System.Threading.Tasks namespace: Tasks are not directly related to threads or multithreading. Of course, Task instances will typically be used in our implementation of concurrency within an application, but the Task class itself does not provide the concurrency used.  The Task API supports using Tasks in an entirely single threaded, synchronous manner. Tasks are very much like standard delegates.  You can execute a task synchronously via Task.RunSynchronously(), or you can use Task.Start() to schedule a task to run, typically asynchronously.  This is very similar to using delegate.Invoke to execute a delegate synchronously, or using delegate.BeginInvoke to execute it asynchronously. The Task class adds some nice functionality on top of a standard delegate which improves usability in both synchronous and multithreaded environments. The first addition provided by Task is a means of handling cancellation via the new unified cancellation mechanism of .NET 4.  If the wrapped delegate within a Task raises an OperationCanceledException during it’s operation, which is typically generated via calling ThrowIfCancellationRequested on a CancellationToken, or if the CancellationToken used to construct a Task instance is flagged as canceled, the Task’s IsCanceled property will be set to true automatically.  This provides a clean way to determine whether a Task has been canceled, often without requiring specific exception handling. Tasks also provide a clean API which can be used for waiting on a task.  Although the Task class explicitly implements IAsyncResult, Tasks provide a nicer usage model than the traditional .NET Asynchronous Programming Model.  Instead of needing to track an IAsyncResult handle, you can just directly call Task.Wait() to block until a Task has completed.  Overloads exist for providing a timeout, a CancellationToken, or both to prevent waiting indefinitely.  In addition, the Task class provides static methods for waiting on multiple tasks – Task.WaitAll and Task.WaitAny, again with overloads providing time out options.  This provides a very simple, clean API for waiting on single or multiple tasks. Finally, Tasks provide a much nicer model for Exception handling.  If the delegate wrapped within a Task raises an exception, the exception will automatically get wrapped into an AggregateException and exposed via the Task.Exception property.  This exception is stored with the Task directly, and does not tear down the application.  Later, when Task.Wait() (or Task.WaitAll or Task.WaitAny) is called on this task, an AggregateException will be raised at that point if any of the tasks raised an exception.  For example, suppose we have the following code: Task taskOne = new Task( () => { throw new ApplicationException("Random Exception!"); }); Task taskTwo = new Task( () => { throw new ArgumentException("Different exception here"); }); // Start the tasks taskOne.Start(); taskTwo.Start(); try { Task.WaitAll(new[] { taskOne, taskTwo }); } catch (AggregateException e) { Console.WriteLine(e.InnerExceptions.Count); foreach (var inner in e.InnerExceptions) Console.WriteLine(inner.Message); } .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, our routine will print: 2 Different exception here Random Exception! Note that we had two separate tasks, each of which raised two distinctly different types of exceptions.  We can handle this cleanly, with very little code, in a much nicer manner than the Asynchronous Programming API.  We no longer need to handle TargetInvocationException or worry about implementing the Event-based Asynchronous Pattern properly by setting the AsyncCompletedEventArgs.Error property.  Instead, we just raise our exception as normal, and handle AggregateException in a single location in our calling code.

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  • SQL SERVER – Integration Services Balanced Data Distributor – SSIS Balanced Data Distributor

    - by pinaldave
    Microsoft SSIS Balanced Data Distributor (BDD) is a new SSIS transform. This transform takes a single input and distributes the incoming rows to one or more outputs uniformly via multithreading. The transform takes one pipeline buffer worth of rows at a time and moves it to the next output in a round robin fashion. It’s balanced and synchronous so if one of the downstream transforms or destinations is slower than the others, the rest of the pipeline will stall so this transform works best if all of the outputs have identical transforms and destinations. Download SQL Server Integration Services Balanced Data Distributor Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Semi-blocking Transformations in SQL Server Integration Services SSIS

    In a SSIS data flow, there are multiple types of transformations. On one hand you have synchronous and asynchronous transformations, but on the other hand you have non-blocking, semi-blocking and fully-blocking components. In this tip, Koen Verbeeck takes a closer look on the performance impact of semi-blocking transformations in SSIS. Can 41,000 DBAs really be wrong? Join 41,000 other DBAs who are following the new series from the DBA Team: the 5 Worst Days in a DBA’s Life. Part 3, As Corrupt As It Gets, is out now – read it here.

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  • C# async and actors

    - by Alex.Davies
    If you read my last post about async, you might be wondering what drove me to write such odd code in the first place. The short answer is that .NET Demon is written using NAct Actors. Actors are an old idea, which I believe deserve a renaissance under C# 5. The idea is to isolate each stateful object so that only one thread has access to its state at any point in time. That much should be familiar, it's equivalent to traditional lock-based synchronization. The different part is that actors pass "messages" to each other rather than calling a method and waiting for it to return. By doing that, each thread can only ever be holding one lock. This completely eliminates deadlocks, my least favourite concurrency problem. Most people who use actors take this quite literally, and there are plenty of frameworks which help you to create message classes and loops which can receive the messages, inspect what type of message they are, and process them accordingly. But I write C# for a reason. Do I really have to choose between using actors and everything I love about object orientation in C#? Type safety Interfaces Inheritance Generics As it turns out, no. You don't need to choose between messages and method calls. A method call makes a perfectly good message, as long as you don't wait for it to return. This is where asynchonous methods come in. I have used NAct for a while to wrap my objects in a proxy layer. As long as I followed the rule that methods must always return void, NAct queued up the call for later, and immediately released my thread. When I needed to get information out of other actors, I could use EventHandlers and callbacks (continuation passing style, for any CS geeks reading), and NAct would call me back in my isolated thread without blocking the actor that raised the event. Using callbacks looks horrible though. To remind you: m_BuildControl.FilterEnabledForBuilding(    projects,    enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(        enabledProjects,             newDirtyProjects =             {                 ....... Which is why I'm really happy that NAct now supports async methods. Now, methods are allowed to return Task rather than just void. I can await those methods, and C# 5 will turn the rest of my method into a continuation for me. NAct will run the other method in the other actor's context, but will make sure that when my method resumes, we're back in my context. Neither actor was ever blocked waiting for the other one. Apart from when they were actually busy doing something, they were responsive to concurrent messages from other sources. To be fair, you could use async methods with lock statements to achieve exactly the same thing, but it's ugly. Here's a realistic example of an object that has a queue of data that gets passed to another object to be processed: class QueueProcessor {    private readonly ItemProcessor m_ItemProcessor = ...     private readonly object m_Sync = new object();    private Queue<object> m_DataQueue = ...    private List<object> m_Results = ...     public async Task ProcessOne() {         object data = null;         lock (m_Sync)         {             data = m_DataQueue.Dequeue();         }         var processedData = await m_ItemProcessor.ProcessData(data); lock (m_Sync)         {             m_Results.Add(processedData);         }     } } We needed to write two lock blocks, one to get the data to process, one to store the result. The worrying part is how easily we could have forgotten one of the locks. Compare that to the version using NAct: class QueueProcessorActor : IActor { private readonly ItemProcessor m_ItemProcessor = ... private Queue<object> m_DataQueue = ... private List<object> m_Results = ... public async Task ProcessOne()     {         // We are an actor, it's always thread-safe to access our private fields         var data = m_DataQueue.Dequeue();         var processedData = await m_ItemProcessor.ProcessData(data);         m_Results.Add(processedData);     } } You don't have to explicitly lock anywhere, NAct ensures that your code will only ever run on one thread, because it's an actor. Either way, async is definitely better than traditional synchronous code. Here's a diagram of what a typical synchronous implementation might do: The left side shows what is running on the thread that has the lock required to access the QueueProcessor's data. The red section is where that lock is held, but doesn't need to be. Contrast that with the async version we wrote above: Here, the lock is released in the middle. The QueueProcessor is free to do something else. Most importantly, even if the ItemProcessor sometimes calls the QueueProcessor, they can never deadlock waiting for each other. So I thoroughly recommend you use async for all code that has to wait a while for things. And if you find yourself writing lots of lock statements, think about using actors as well. Using actors and async together really takes the misery out of concurrent programming.

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  • How to write reusable code in node.js

    - by lortabac
    I am trying to understand how to design node.js applications, but it seems there is something I can't grasp about asynchronous programming. Let's say my application needs to access a database. In a synchronous environment I would implement a data access class with a read() method, returning an associative array. In node.js, because code is executed asynchronously, this method can't return a value, so, after execution, it will have to "do" something as a side effect. It will then contain some code which does something else than just reading data. Let's suppose I want to call this method multiple times, each time with a different success callback. Since the callback is included in the method itself, I can't find a clean way to do this without either duplicating the method or specifying all possible callbacks in a long switch statement. What is the proper way to handle this problem? Am I approaching it the wrong way?

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  • How can I switch memory modules to 1600 Mhz?

    - by Salvador
    Some months ago I bought 4 Memory modules of 4GB DDR3 1600 KINGSTON HYPERX. The official Kingston manual says: *This module has been tested to run at DDR3-1600 at a low latency timing of 9-9-9-27 at 1.65V.The SPD is programmed to JEDEC standard latency DDR3-1333 timing of 9-9-9. I cannot find which is the real speed of my memory modules. I normally get from several tools that the real speed is 1333 Mhz srs@ubuntu:~$ sudo dmidecode -t memory # dmidecode 2.9 SMBIOS 2.6 present. Handle 0x005D, DMI type 16, 15 bytes Physical Memory Array Location: System Board Or Motherboard Use: System Memory Error Correction Type: None Maximum Capacity: 32 GB Error Information Handle: 0x005F Number Of Devices: 4 Handle 0x005C, DMI type 17, 28 bytes Memory Device Array Handle: 0x005D Error Information Handle: 0x0060 Total Width: 64 bits Data Width: 64 bits Size: 4096 MB Form Factor: DIMM Set: None Locator: ChannelA-DIMM0 Bank Locator: BANK 0 Type: <OUT OF SPEC> Type Detail: Synchronous Speed: 1333 MHz (0.8 ns) Manufacturer: Kingston Serial Number: 07288F23 Asset Tag: 9876543210 Part Number: 9905403-439.A00LF How can I switch memory modules to 1600 Mhz?

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  • Organization &amp; Architecture UNISA Studies &ndash; Chap 5

    - by MarkPearl
    Learning Outcomes Describe the operation of a memory cell Explain the difference between DRAM and SRAM Discuss the different types of ROM Explain the concepts of a hard failure and a soft error respectively Describe SDRAM organization Semiconductor Main Memory The two traditional forms of RAM used in computers are DRAM and SRAM DRAM (Dynamic RAM) Divided into two technologies… Dynamic Static Dynamic RAM is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0. Because capacitors have natural tendency to discharge, dynamic RAM requires periodic charge refreshing to maintain data storage. The term dynamic refers to the tendency of the stored charge to leak away, even with power continuously applied. Although the DRAM cell is used to store a single bit (0 or 1), it is essentially an analogue device. The capacitor can store any charge value within a range, a threshold value determines whether the charge is interpreted as a 1 or 0. SRAM (Static RAM) SRAM is a digital device that uses the same logic elements used in the processor. In SRAM, binary values are stored using traditional flip flop logic configurations. SRAM will hold its data as along as power is supplied to it. Unlike DRAM, no refresh is required to retain data. SRAM vs. DRAM DRAM is simpler and smaller than SRAM. Thus it is more dense and less expensive than SRAM. The cost of the refreshing circuitry for DRAM needs to be considered, but if the machine requires a large amount of memory, DRAM turns out to be cheaper than SRAM. SRAMS are somewhat faster than DRAM, thus SRAM is generally used for cache memory and DRAM is used for main memory. Types of ROM Read Only Memory (ROM) contains a permanent pattern of data that cannot be changed. ROM is non volatile meaning no power source is required to maintain the bit values in memory. While it is possible to read a ROM, it is not possible to write new data into it. An important application of ROM is microprogramming, other applications include library subroutines for frequently wanted functions, System programs, Function tables. A ROM is created like any other integrated circuit chip, with the data actually wired into the chip as part of the fabrication process. To reduce costs of fabrication, we have PROMS. PROMS are… Written only once Non-volatile Written after fabrication Another variation of ROM is the read-mostly memory, which is useful for applications in which read operations are far more frequent than write operations, but for which non volatile storage is required. There are three common forms of read-mostly memory, namely… EPROM EEPROM Flash memory Error Correction Semiconductor memory is subject to errors, which can be classed into two categories… Hard failure – Permanent physical defect so that the memory cell or cells cannot reliably store data Soft failure – Random error that alters the contents of one or more memory cells without damaging the memory (common cause includes power supply issues, etc.) Most modern main memory systems include logic for both detecting and correcting errors. Error detection works as follows… When data is to be read into memory, a calculation is performed on the data to produce a code Both the code and the data are stored When the previously stored word is read out, the code is used to detect and possibly correct errors The error checking provides one of 3 possible results… No errors are detected – the fetched data bits are sent out An error is detected, and it is possible to correct the error. The data bits plus error correction bits are fed into a corrector, which produces a corrected set of bits to be sent out An error is detected, but it is not possible to correct it. This condition is reported Hamming Code See wiki for detailed explanation. We will probably need to know how to do a hemming code – refer to the textbook (pg. 188 – 189) Advanced DRAM organization One of the most critical system bottlenecks when using high-performance processors is the interface to main memory. This interface is the most important pathway in the entire computer system. The basic building block of main memory remains the DRAM chip. In recent years a number of enhancements to the basic DRAM architecture have been explored, and some of these are now on the market including… SDRAM (Synchronous DRAM) DDR-DRAM RDRAM SDRAM (Synchronous DRAM) SDRAM exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states. SDRAM employs a burst mode to eliminate the address setup time and row and column line precharge time after the first access In burst mode a series of data bits can be clocked out rapidly after the first bit has been accessed SDRAM has a multiple bank internal architecture that improves opportunities for on chip parallelism SDRAM performs best when it is transferring large blocks of data serially There is now an enhanced version of SDRAM known as double data rate SDRAM or DDR-SDRAM that overcomes the once-per-cycle limitation of SDRAM

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  • 12c??? - Active Data Guard Far Sync

    - by Jian Zhang(??)
    ?? ================ Active Data Guard Far Sync?Oracle 12c????(???Far Sync Standby),Far Sync?????????????(Primary Database)?????????Far Sync??,??(Primary Database) ??(synchronous)??redo?Far Sync??,??Far Sync????redo??(asynchronous)???????(Standby Database)???????????????????????Far Sync????????,init?????????,???????? ??redo ????Maximum Availability??,???????????(Primary Database)?????????Far Sync??,??(Primary Database)??(synchronous)??redo?Far Sync??,???????(zero data loss),?????Far Sync????,??????,??????????????Far Sync????redo??(asynchronous)???????(Standby Database)? ??redo ????Maximum Performance??,???????????(Primary Database)?????????Far Sync??,??(Primary Database) ????redo?Far Sync??,??Far Sync???????redo?????????(Standby Database)????????????????(Standby Database)??redo???(offload)? Far Sync????Data Guard ????(role transitions)????,?switchover/failover?????12c????? ???????Data Guard ????,?switchover/failover,???????????????Far Sync??,??Far Sync???????????????????? ???Far Sync???????,??????????????2?Far Sync??,???????? ???????Far Sync????? Far Sync??? ================ ????Far Sync ================ 1. ??Data Guard,???11.2??,??????«Active Database Duplication for A standby database» 2. ????Far Sync??,Far Sync????????,init?????????,???????? ??Far Sync???????,?????: SQL> ALTER DATABASE CREATE FAR SYNC INSTANCE CONTROLFILE AS '/tmp/controlfs01.ctl'; 3. ????redo?????Far Sync??,????LOG_ARCHIVE_DEST_2??: LOG_ARCHIVE_DEST_2='SERVICE=dg12cfs SYNC AFFIRM MAX_FAILURE=1 ALTERNATE=LOG_ARCHIVE_DEST_3 VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=dg12cfs' 4. ??Far Sync??????redo???,??Far Sync??LOG_ARCHIVE_DEST_2??: LOG_ARCHIVE_DEST_2='SERVICE=dg12cs ASYNC VALID_FOR=(STANDBY_LOGFILES,STANDBY_ROLE) DB_UNIQUE_NAME=dg12cs' 5. ????Far Sync???????,??????????????2?Far Sync??? 6. ???????: SQL> select * from  V$DATAGUARD_CONFIG; DB_UNIQUE_NAME       PARENT_DBUN       DEST_ROLE         CURRENT_SCN     CON_ID ------------------------------ ------------------------------     ----------------- ----------- ---------- dg12cfs                        dg12cp          FAR SYNC INSTANCE      682995          0 dg12cs                         dg12cfs         PHYSICAL STANDBY       682995          0 dg12cp                        NONE             PRIMARY DATABASE      683138          0 ????????????????:Oracle_12c_Active_Data_Guard_Far_Sync_v1.pdf

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  • Tuesday at Oracle OpenWorld 2012 - Must See Session: “Oracle Fusion Applications: Best Practices in Integration Design Patterns”

    - by Lionel Dubreuil
    Don’t miss this “CON8685 - Oracle Fusion Applications: Best Practices in Integration Design Patterns “ session: Speakers: Rajesh Raheja - Senior Director, Development, Oracle Ravi Sankaran - Director, Applications Development, Oracle Date: Tuesday, Oct 2 Time: 1:15 PM - 2:15 PM Location: Palace Hotel - Telegraph Oracle Fusion Applications provide various ways to integrate their functional capabilities with other Oracle applications as well as third-party and legacy applications. In this session, you will learn the patterns used when communicating with Oracle Fusion Applications with a SOA approach. It addresses items related to identifying the integration artifacts available, also known as assets, in Oracle Enterprise Repository; how to invoke synchronous and asynchronous Web services; importing and exporting bulk data; and any integration issues to look out for. The patterns will be applicable to on-premises and SaaS/cloud deployment modes and are indicated as such. Objectives for this session are to: Highlight the various ways to integrate with Oracle Fusion Applications Showcase use of Oracle Fusion Middleware technologies for integration Describe best practices and design patterns for integration

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  • Tuesday at Oracle OpenWorld 2012 - Must See Session: “Oracle Fusion Applications: Best Practices in Integration Design Patterns”

    - by Lionel Dubreuil
    Don’t miss this “CON8685 - Oracle Fusion Applications: Best Practices in Integration Design Patterns “ session: Speakers: Rajesh Raheja - Senior Director, Development, Oracle Ravi Sankaran - Director, Applications Development, Oracle Date: Tuesday, Oct 2 Time: 1:15 PM - 2:15 PM Location: Palace Hotel - Telegraph Oracle Fusion Applications provide various ways to integrate their functional capabilities with other Oracle applications as well as third-party and legacy applications. In this session, you will learn the patterns used when communicating with Oracle Fusion Applications with a SOA approach. It addresses items related to identifying the integration artifacts available, also known as assets, in Oracle Enterprise Repository; how to invoke synchronous and asynchronous Web services; importing and exporting bulk data; and any integration issues to look out for. The patterns will be applicable to on-premises and SaaS/cloud deployment modes and are indicated as such. Objectives for this session are to: Highlight the various ways to integrate with Oracle Fusion Applications Showcase use of Oracle Fusion Middleware technologies for integration Describe best practices and design patterns for integration

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