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  • boost::asio::async_resolve Problem

    - by Moo-Juice
    Hi All, I'm in the process of constructing a Socket class that uses boost::asio. To start with, I made a connect method that took a host and a port and resolved it to an IP address. This worked well, so I decided to look in to async_resolve. However, my callback always gets an error code of 995 (using the same destination host/port as when it worked synchronously). code: Function that starts the resolution: // resolve a host asynchronously template<typename ResolveHandler> void resolveHost(const String& _host, Port _port, ResolveHandler _handler) const { boost::asio::ip::tcp::endpoint ret; boost::asio::ip::tcp::resolver::query query(_host, boost::lexical_cast<std::string>(_port)); boost::asio::ip::tcp::resolver r(m_IOService); r.async_resolve(query, _handler); }; // eo resolveHost Code that calls this function: void Socket::connect(const String& _host, Port _port) { // Anon function for resolution of the host-name and asynchronous calling of the above auto anonResolve = [this](const boost::system::error_code& _errorCode, boost::asio::ip::tcp::resolver_iterator _epIt) { // raise event onResolve.raise(SocketResolveEventArgs(*this, !_errorCode ? (*_epIt).host_name() : String(""), _errorCode)); // perform connect, calling back to anonymous function if(!_errorCode) connect(*_epIt); }; // Resolve the host calling back to anonymous function Root::instance().resolveHost(_host, _port, anonResolve); }; // eo connect The message() function of the error_code is: The I/O operation has been aborted because of either a thread exit or an application request And my main.cpp looks like this: int _tmain(int argc, _TCHAR* argv[]) { morse::Root root; TextSocket s; s.connect("somehost.com", 1234); while(true) { root.performIO(); // calls io_service::run_one() } return 0; } Thanks in advance!

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  • WCF Async callback setup for polled device

    - by Mark Pim
    I have a WCF service setup to control a USB fingerprint reader from our .Net applications. This works fine and I can ask it to enroll users and so on. The reader allows identification (it tells you that a particular user has presented their finger, as opposed to asking it to verify that a particular user's finger is present), but the device must be constantly polled while in identification mode for its status - when a user is detected the status changes. What I want is for an interested application to notify the service that it wants to know when a user is identified, and provide a callback that gets triggered when this happens. The WCF service will return immediately and spawn a thread in the background to continuously poll the device. This polling could go on for hours at a time if no one tries to log in. What's the best way to acheive this? My service contract is currently defined as follows: [ServiceContract (CallbackContract=typeof(IBiometricCallback))] public interface IBiometricWcfService { ... [OperationContract (IsOneWay = true)] void BeginIdentification(); ... } public interface IBiometricCallback { ... [OperationContract(IsOneWay = true)] void IdentificationFinished(int aUserId, string aMessage, bool aSuccess); ... } In my BeginIdentification() method can I easily spawn a worker thread to poll the device, or is it easier to make the WCF service asynchronous?

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  • InvalidOperationException: The Undo operation encountered a context that is different from what was

    - by McN
    I got the following exception: Exception Type: System.InvalidOperationException Exception Message: The Undo operation encountered a context that is different from what was applied in the corresponding Set operation. The possible cause is that a context was Set on the thread and not reverted(undone). Exception Stack: at System.Threading.SynchronizationContextSwitcher.Undo() at System.Threading.ExecutionContextSwitcher.Undo() at System.Threading.ExecutionContext.runFinallyCode(Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteBackoutCodeHelper(Object backoutCode, Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.ContextAwareResult.Complete(IntPtr userToken) at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken) at System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) Exception Source: mscorlib Exception TargetSite.Name: Undo Exception HelpLink: The application is a Visual Studio 2005 (.Net 2.0) console application. It is a server for multiple TCP/IP connections, doing asynchronous socket reads and synchronous socket writes. In searching for an answer I came across this post which talks about a call to Application.Doevents() which I don't use in my code. I also found this post which has a resolution involved with Component which I also don't use in my code. The application does reference a library that I created that contains custom user controls and components, but they are not being used by the application. Question: What caused this to happen and how do I prevent this from happening again? Or a more realistic question: What does this exception actually mean? How is "context" defined in this situation? Anything that can help me understand what is going on would be very much appreciated.

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  • Two pass JSP page rendering

    - by dotsid
    Suppose an example. I have following interface: public interface DataSource<T> { Future<T> fetch(); } This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP: <html> <d:fetch from="${orderDS}" var="orders"> <c:foreach in="${orders}" var="order"> <div class="order"> <c:out value="${order.title}" /> </div> </c:foreach> </d:fetch> </html> So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available. Is there any way to do such a thing?

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  • Execute a block of database querys

    - by Nightmare
    I have the following task to complete: In my program a have a block of database querys or questions. I want to execute these questions and wait for the result of all questions or catch an error if one question fails! My Question object looks like this (simplified): public class DbQuestion(String sql) { [...] } [...] //The answer is just a holder for custom data... public void SetAnswer(DbAnswer answer) { //Store the answer in the question and fire a event to the listeners this.OnAnswered(EventArgs.Empty); } [...] public void SetError() { //Signal an Error in this query! this.OnError(EventArgs.Empty); } So every question fired to the database has a listener that waits for the parsed result. Now I want to fire some questions asynchronous to the database (max. 5 or so) and fire an event with the data from all questions or an error if only one question throws one! Which is the best or a good way to accomplish this task? Can I really execute more then one question parallel and stop all my work when one question throws an error? I think I need some inspiration on this... Just a note: I´m working with .NET framework 2.0

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  • callback on a variable which is inside a .each() loop

    - by Stoic
    I have this function, which is doing an asynchronous call to FB.api method. Now, i am looping over some data and capturing result of the above method call successfully. However, I am using a .each loop and I really can not figure out how to place my callback in this method, so that the outer method is only executed once. Here are the functions I am using: ask_for_perms($(this).val(),function(result) { $('#some-div').html('<a onclick = "get_perms(result);" >get perms</a>'); }); function ask_for_perms(perms_requested,cb) { var request = []; $.each(perms_requested,function(i,permission) { FB.api({ method: 'users.hasAppPermission', ext_perm: permission }, function(response) { if (response == 0) request.push(permission); request.join(','); cb(request); // cb is called many times here. }); }); } I am trying to return the request string from ask_for_perms function. Can anyone suggest me on where to place a proper callback to ask_for_perms. Right now, however, it works for me, but the callback is being called many times since it is inside a for loop. referencing: returning a variable from the callback of a function

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  • how get fully result from Asynchronism communication?

    - by rima
    Hi all refer to these post : here1 and here2 at last I solve my problem by build a asynchronous solution,and it work well!!! but there is a problem that i face with it,now my code is like this: class MyProcessStarter { private Process process; private StreamWriter myStreamWriter; private static StringBuilder shellOutput = null; public String GetShellOutput { get { return shellOutput.ToString(); }} public MyProcessStarter(){ shellOutput = new StringBuilder(""); process = new Process(); process.StartInfo.FileName = "sqlplus"; process.StartInfo.UseShellExecute = false; process.StartInfo.CreateNoWindow = true; process.OutputDataReceived += new DataReceivedEventHandler(ShellOutputHandler); process.StartInfo.RedirectStandardInput = true; process.StartInfo.RedirectStandardOutput = true; //process.StartInfo.RedirectStandardError = true; process.Start(); myStreamWriter = process.StandardInput; process.BeginOutputReadLine(); } private static void ShellOutputHandler(object sendingProcess,DataReceivedEventArgs outLine) { if (!String.IsNullOrEmpty(outLine.Data)) shellOutput.Append(Environment.NewLine + outLine.Data); } public void closeConnection() { myStreamWriter.Close(); process.WaitForExit(); process.Close(); } public void RunCommand(string arguments) { myStreamWriter.WriteLine(arguments); myStreamWriter.Flush(); process.WaitForExit(100); Console.WriteLine(shellOutput); Console.WriteLine("============="+Environment.NewLine); process.WaitForExit(2000); Console.WriteLine(shellOutput); } } and my input is like this: myProcesStarter.RunCommand("myusername/mypassword"); Console.writeline(myProcesStarter.GetShellOutput); but take a look at my out put: SQL*Plus: Release 11.1.0.6.0 - Production on Thu May 20 11:57:38 2010 Copyright (c) 1982, 2007, Oracle. All rights reserved. ============= SQL*Plus: Release 11.1.0.6.0 - Production on Thu May 20 11:57:38 2010 Copyright (c) 1982, 2007, Oracle. All rights reserved. Enter user-name: Connected to: Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production With the Partitioning, OLAP, Data Mining and Real Application Testing options as u see the output for run a function is not same in different time!So now would you do me a faver and help me that how I can wait until all the output done in other mean how I can customize my process to wait until output finishing ?? because I want to write a sqlcompiler so I need the exact output of shell. plz help me soon.thanxxxxxxxxxxxx :X

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  • jQuery post request is not sent until first post request is compleated

    - by Champ
    I have a function which have a long execution time. public void updateCampaign() { context.Session[processId] = "0|Fetching Lead360 Campaign"; Lead360 objLead360 = new Lead360(); string campaignXML = objLead360.getCampaigns(); string todayDate = DateTime.Now.ToString("dd-MMMM-yyyy"); context.Session[processId] = "1|Creating File for Lead360 Campaign on " + todayDate; string fileName = HttpContext.Current.Server.MapPath("campaigns") + todayDate + ".xml"; objLead360.createFile(fileName, campaignXML); context.Session[processId] = "2|Reading The latest Lead360 Campaign"; string file = File.ReadAllText(fileName); context.Session[processId] = "3|Updating Lead360 Campaign"; string updateStatus = objLead360.updateCampaign(fileName); string[] statusArr = updateStatus.Split('|'); context.Session[processId] = "99|" + statusArr[0] + " New Inserted , " + statusArr[1] + " Updated , With " + statusArr[2] + " Error , "; } So to track the Progress of the function I wrote a another function public void getProgress() { if (context.Session[processId] == null) { string json = "{\"error\":true}"; Response.Write(json); Response.End(); }else{ string[] status = context.Session[processId].ToString().Split('|'); if (status[0] == "99") context.Session.Remove(processId); string json = "{\"error\":false,\"statuscode\":" + status[0] + ",\"statusmsz\":\"" + status[1] + "\" }"; Response.Write(json); Response.End(); } } To call this by jQuery post request is used reqUrl = "AjaxPages/lead360Campaign.aspx?processid=" + progressID + "&action=updatecampaign"; $.post(reqUrl); setTimeout(getProgress, 500); get getProgress is : function getProgress() { reqUrl = "AjaxPages/lead360Campaign.aspx?processid=" + progressID + "&action=getProgress"; $.post(reqUrl, function (response) { var progress = jQuery.parseJSON(response); console.log(progress) if (progress.error) { $("#fetchedCampaign .waitingMsz").html("Some error occured. Please try again later."); $("#fetchedCampaign .waitingMsz").css({ "background": "url(common/images/ajax_error.jpg) no-repeat center 6px" }); return; } if (progress.statuscode == 99) { $("#fetchedCampaign .waitingMsz").html("Update Status :"+ progress.statusmsz ); $("#fetchedCampaign .waitingMsz").css({ "background": "url(common/images/ajax_loded.jpg) no-repeat center 6px" }); return; } $("#fetchedCampaign .waitingMsz").html("Please Wait... " + progress.statusmsz); setTimeout(getProgress, 500); }); } But the problem is that I can't see the intermediate message. Only the last message is been displayed after a long lime of ajax loading message Also on the browser console I just see that after a long time first requested is completed and after that the second request is completed. but there should be for getProgress ? I have checked jquery.doc and it says that $post is an asynchronous request. Can anyone please explain what is wrong with the code or logic?

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  • Can an asynchronously fired event run synchronously on a form?

    - by cyclotis04
    [VS 2010 Beta with .Net Framework 3.5] I've written a C# component to asynchronously monitor a socket and raise events when data is received. I set the VB form to show message boxes when the event is raised. What I've noticed is that when the component raises the event synchronously, the message box blocks the component code and locks the form until the user closes the message. When it's raised asynchronously, it neither blocks the code, nor locks the form. What I want is a way to raise an event in such a way that it does not block the code, but is called on the same thread as the form (so that it locks the form until the user selects an option.) Can you help me out? Thanks. [Component] using System; using System.Threading; using System.ComponentModel; namespace mySpace { public delegate void SyncEventHandler(object sender, SyncEventArgs e); public delegate void AsyncEventHandler(object sender, AsyncEventArgs e); public class myClass { readonly object syncEventLock = new object(); readonly object asyncEventLock = new object(); SyncEventHandler syncEvent; AsyncEventHandler asyncEvent; private delegate void WorkerDelegate(string strParam, int intParam); public void DoWork(string strParam, int intParam) { OnSyncEvent(new SyncEventArgs()); AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null); WorkerDelegate delWorker = new WorkerDelegate(ClientWorker); IAsyncResult result = delWorker.BeginInvoke(strParam, intParam, null, null); } private void ClientWorker(string strParam, int intParam) { Thread.Sleep(2000); OnAsyncEvent(new AsyncEventArgs()); OnAsyncEvent(new AsyncEventArgs()); } public event SyncEventHandler SyncEvent { add { lock (syncEventLock) syncEvent += value; } remove { lock (syncEventLock) syncEvent -= value; } } public event AsyncEventHandler AsyncEvent { add { lock (asyncEventLock) asyncEvent += value; } remove { lock (asyncEventLock) asyncEvent -= value; } } protected void OnSyncEvent(SyncEventArgs e) { SyncEventHandler handler; lock (syncEventLock) handler = syncEvent; if (handler != null) handler(this, e, null, null); // Blocks and locks //if (handler != null) handler.BeginInvoke(this, e, null, null); // Neither blocks nor locks } protected void OnAsyncEvent(AsyncEventArgs e) { AsyncEventHandler handler; lock (asyncEventLock) handler = asyncEvent; //if (handler != null) handler(this, e, null, null); // Blocks and locks if (handler != null) handler.BeginInvoke(this, e, null, null); // Neither blocks nor locks } } } [Form] Imports mySpace Public Class Form1 Public WithEvents component As New mySpace.myClass() Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click component.DoWork("String", 1) End Sub Private Sub component_SyncEvent(ByVal sender As Object, ByVal e As pbxapi.SyncEventArgs) Handles component.SyncEvent MessageBox.Show("Synchronous event", "Raised:", MessageBoxButtons.OK) End Sub Private Sub component_AsyncEvent(ByVal sender As Object, ByVal e As pbxapi.AsyncEventArgs) Handles component.AsyncEvent MessageBox.Show("Asynchronous event", "Raised:", MessageBoxButtons.OK) End Sub End Class

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  • Synchronous vs. asynchronous for publish subscribe communication between JavaScript objects

    - by natlee75
    I implemented the publish subscribe pattern in a JavaScript module to be used by entirely client-side oriented JavaScript objects. This module has nothing to do with client-server communications in any way, shape or form. My question is whether it's better for the publish method in such a module to be synchronous or asynchronous, and why. As a very simplified example let's say I'm building a custom UI for an HTML5 video player widget: One of my modules is the "video" module that contains the VIDEO element and handles the various features and events associated with that element. This would probably have a namespace something like "widgets.player.video." Another is the "controls" module that has the various buttons - play, pause, volume, scrub, fullscreen, etc. This might have a namespace along the lines of "widgets.player.controls." These two modules are children of a parent "player" module ("widgets.player" ??), and as such would have no inherent knowledge of each other when instantiated as children of the "player" object. The "controls" elements would obviously need to be able to effect some changes on the video (click "Play" and the video should play), and vice versa (video's "timeUpdate" event fires and the visual display of the current time in the controls should update). I could tightly couple these modules and pass references to each other, but I'd rather take a more loosely coupled approach by setting up a pubsub type module that both can subscribe to and publish from. SO (thanks for bearing with me) in this kind of a scenario is there an advantage one way or another for synchronous publication versus asynchronous publication? I've seen some solutions posted online that allow for either/or with a boolean flag whereas others automatically do it asynchronously. I haven't personally seen an implementation that just automatically goes with synchronous publication... is this because there's no advantage to it? I know that I can accomplish this with features provided by jQuery, but it seems that there may be too much overhead involved here. The publish subscribe pattern can be implemented with relatively lightweight code designed specifically for this particular purpose so I'd rather go with that then a more general purpose eventing system like jQuery's (which I'll use for more general eventing needs :-).

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  • Asp.Net MVC and ajax async callback execution order

    - by lrb
    I have been sorting through this issue all day and hope someone can help pinpoint my problem. I have created a "asynchronous progress callback" type functionality in my app using ajax. When I strip the functionality out into a test application I get the desired results. See image below: Desired Functionality When I tie the functionality into my single page application using the same code I get a sort of blocking issue where all requests are responded to only after the last task has completed. In the test app above all request are responded to in order. The server reports a ("pending") state for all requests until the controller method has completed. Can anyone give me a hint as to what could cause the change in behavior? Not Desired Desired Fiddler Request/Response GET http://localhost:12028/task/status?_=1383333945335 HTTP/1.1 X-ProgressBar-TaskId: 892183768 Accept: */* X-Requested-With: XMLHttpRequest Referer: http://localhost:12028/ Accept-Language: en-US Accept-Encoding: gzip, deflate User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0) Connection: Keep-Alive DNT: 1 Host: localhost:12028 HTTP/1.1 200 OK Cache-Control: private Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Server: Microsoft-IIS/8.0 X-AspNetMvc-Version: 3.0 X-AspNet-Version: 4.0.30319 X-SourceFiles: =?UTF-8?B?QzpcUHJvamVjdHNcVEVNUFxQcm9ncmVzc0Jhclx0YXNrXHN0YXR1cw==?= X-Powered-By: ASP.NET Date: Fri, 01 Nov 2013 21:39:08 GMT Content-Length: 25 Iteration completed... Not Desired Fiddler Request/Response GET http://localhost:60171/_Test/status?_=1383341766884 HTTP/1.1 X-ProgressBar-TaskId: 838217998 Accept: */* X-Requested-With: XMLHttpRequest Referer: http://localhost:60171/Report/Index Accept-Language: en-US Accept-Encoding: gzip, deflate User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0) Connection: Keep-Alive DNT: 1 Host: localhost:60171 Pragma: no-cache Cookie: ASP.NET_SessionId=rjli2jb0wyjrgxjqjsicdhdi; AspxAutoDetectCookieSupport=1; TTREPORTS_1_0=CC2A501EF499F9F...; __RequestVerificationToken=6klOoK6lSXR51zCVaDNhuaF6Blual0l8_JH1QTW9W6L-3LroNbyi6WvN6qiqv-PjqpCy7oEmNnAd9s0UONASmBQhUu8aechFYq7EXKzu7WSybObivq46djrE1lvkm6hNXgeLNLYmV0ORmGJeLWDyvA2 HTTP/1.1 200 OK Cache-Control: private Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Server: Microsoft-IIS/8.0 X-AspNetMvc-Version: 4.0 X-AspNet-Version: 4.0.30319 X-SourceFiles: =?UTF-8?B?QzpcUHJvamVjdHNcSUxlYXJuLlJlcG9ydHMuV2ViXHRydW5rXElMZWFybi5SZXBvcnRzLldlYlxfVGVzdFxzdGF0dXM=?= X-Powered-By: ASP.NET Date: Fri, 01 Nov 2013 21:37:48 GMT Content-Length: 25 Iteration completed... The only difference in the two requests headers besides the auth tokens is "Pragma: no-cache" in the request and the asp.net version in the response. Thanks Update - Code posted (I probably need to indicate this code originated from an article by Dino Esposito ) var ilProgressWorker = function () { var that = {}; that._xhr = null; that._taskId = 0; that._timerId = 0; that._progressUrl = ""; that._abortUrl = ""; that._interval = 500; that._userDefinedProgressCallback = null; that._taskCompletedCallback = null; that._taskAbortedCallback = null; that.createTaskId = function () { var _minNumber = 100, _maxNumber = 1000000000; return _minNumber + Math.floor(Math.random() * _maxNumber); }; // Set progress callback that.callback = function (userCallback, completedCallback, abortedCallback) { that._userDefinedProgressCallback = userCallback; that._taskCompletedCallback = completedCallback; that._taskAbortedCallback = abortedCallback; return this; }; // Set frequency of refresh that.setInterval = function (interval) { that._interval = interval; return this; }; // Abort the operation that.abort = function () { // if (_xhr !== null) // _xhr.abort(); if (that._abortUrl != null && that._abortUrl != "") { $.ajax({ url: that._abortUrl, cache: false, headers: { 'X-ProgressBar-TaskId': that._taskId } }); } }; // INTERNAL FUNCTION that._internalProgressCallback = function () { that._timerId = window.setTimeout(that._internalProgressCallback, that._interval); $.ajax({ url: that._progressUrl, cache: false, headers: { 'X-ProgressBar-TaskId': that._taskId }, success: function (status) { if (that._userDefinedProgressCallback != null) that._userDefinedProgressCallback(status); }, complete: function (data) { var i=0; }, }); }; // Invoke the URL and monitor its progress that.start = function (url, progressUrl, abortUrl) { that._taskId = that.createTaskId(); that._progressUrl = progressUrl; that._abortUrl = abortUrl; // Place the Ajax call _xhr = $.ajax({ url: url, cache: false, headers: { 'X-ProgressBar-TaskId': that._taskId }, complete: function () { if (_xhr.status != 0) return; if (that._taskAbortedCallback != null) that._taskAbortedCallback(); that.end(); }, success: function (data) { if (that._taskCompletedCallback != null) that._taskCompletedCallback(data); that.end(); } }); // Start the progress callback (if any) if (that._userDefinedProgressCallback == null || that._progressUrl === "") return this; that._timerId = window.setTimeout(that._internalProgressCallback, that._interval); }; // Finalize the task that.end = function () { that._taskId = 0; window.clearTimeout(that._timerId); } return that; };

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  • Asynchrony in C# 5 (Part I)

    - by javarg
    I’ve been playing around with the new Async CTP preview available for download from Microsoft. It’s amazing how language trends are influencing the evolution of Microsoft’s developing platform. Much effort is being done at language level today than previous versions of .NET. In these post series I’ll review some major features contained in this release: Asynchronous functions TPL Dataflow Task based asynchronous Pattern Part I: Asynchronous Functions This is a mean of expressing asynchronous operations. This kind of functions must return void or Task/Task<> (functions returning void let us implement Fire & Forget asynchronous operations). The two new keywords introduced are async and await. async: marks a function as asynchronous, indicating that some part of its execution may take place some time later (after the method call has returned). Thus, all async functions must include some kind of asynchronous operations. This keyword on its own does not make a function asynchronous thought, its nature depends on its implementation. await: allows us to define operations inside a function that will be awaited for continuation (more on this later). Async function sample: Async/Await Sample async void ShowDateTimeAsync() {     while (true)     {         var client = new ServiceReference1.Service1Client();         var dt = await client.GetDateTimeTaskAsync();         Console.WriteLine("Current DateTime is: {0}", dt);         await TaskEx.Delay(1000);     } } The previous sample is a typical usage scenario for these new features. Suppose we query some external Web Service to get data (in this case the current DateTime) and we do so at regular intervals in order to refresh user’s UI. Note the async and await functions working together. The ShowDateTimeAsync method indicate its asynchronous nature to the caller using the keyword async (that it may complete after returning control to its caller). The await keyword indicates the flow control of the method will continue executing asynchronously after client.GetDateTimeTaskAsync returns. The latter is the most important thing to understand about the behavior of this method and how this actually works. The flow control of the method will be reconstructed after any asynchronous operation completes (specified with the keyword await). This reconstruction of flow control is the real magic behind the scene and it is done by C#/VB compilers. Note how we didn’t use any of the regular existing async patterns and we’ve defined the method very much like a synchronous one. Now, compare the following code snippet  in contrast to the previuous async/await: Traditional UI Async void ComplicatedShowDateTime() {     var client = new ServiceReference1.Service1Client();     client.GetDateTimeCompleted += (s, e) =>     {         Console.WriteLine("Current DateTime is: {0}", e.Result);         client.GetDateTimeAsync();     };     client.GetDateTimeAsync(); } The previous implementation is somehow similar to the first shown, but more complicated. Note how the while loop is implemented as a chained callback to the same method (client.GetDateTimeAsync) inside the event handler (please, do not do this in your own application, this is just an example).  How it works? Using an state workflow (or jump table actually), the compiler expands our code and create the necessary steps to execute it, resuming pending operations after any asynchronous one. The intention of the new Async/Await pattern is to let us think and code as we normally do when designing and algorithm. It also allows us to preserve the logical flow control of the program (without using any tricky coding patterns to accomplish this). The compiler will then create the necessary workflow to execute operations as the happen in time.

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  • Relationship between "Task Parallel Library" and "Task-based Asynchronous Pattern"?

    - by Sid
    In the context of C#, .NET 4/4.5 used for an application running on a web-server, what is the relationship between "Task Parallel Library" and "Task-based Asynchronous Pattern"? I understand one is a library and the other is a pattern. But to dig deeper, is it like "The library is used by the pattern to enforce good practices". I'm also not clear if both are supported in .NET 4.0 (with awake and async keywords) Edit: Seems that awake and async are only in .NET 4.5 ...

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  • [C#] WebClient - Upload data, get stream

    - by Barguast
    I have a situation where I want to asynchronously write a series of bytes with WebClient (in much the same way as UploadDataAsync) and get a readable response stream (in the same way as OpenReadAsync). You seem to be able to do the two individually, but not both of them together. Is there a way? Thanks!

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  • WCF: Server Not Found - from trace Empty Message when run async but works fine from console app?

    - by MrTortoise
    Todays cause of hair loss has been the following scenario: I have a service that takes 2 strings and returns another. This service uses basicHttpBinding <basicHttpBinding> <binding name="basicHttpNoSec"> <security mode="None" /> </binding> </basicHttpBinding> Anyway, it works fine from a console test app. I have a silverlight app sat on top which implements another basicHttpBinding service that simply reuses the contract in the other service and the silverlight App uses this service. I have a console app that confirms that this service is working and set up with basichttpbinding. I have all the clientAccessPolicy stuff in place. when I run the silverlight app the difference is that it runs everything async ... as such the only message i directly get back rom wcf is server not found. When i enable tracing I dig down to this message - as I know the methods work and the parameteres i pass in will return a valid string i am really puzzled at to what the cause is. any help much appreciated. <E2ETraceEvent xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent"> <System xmlns="http://schemas.microsoft.com/2004/06/windows/eventlog/system"> <EventID>131075</EventID> <Type>3</Type> <SubType Name="Error">0</SubType> <Level>2</Level> <TimeCreated SystemTime="2010-06-07T14:17:40.6639249Z" /> <Source Name="System.ServiceModel" /> <Correlation ActivityID="{8ea9530e-12f4-4a82-9c26-dd2e23264c3c}" /> <Execution ProcessName="aspnet_wp" ProcessID="4616" ThreadID="6" /> <Channel /> <Computer>5JC2Y2J</Computer> </System> <ApplicationData> <TraceData> <DataItem> <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Error"> <TraceIdentifier>http://msdn.microsoft.com/en-GB/library/System.ServiceModel.Diagnostics.ThrowingException.aspx</TraceIdentifier> <Description>Throwing an exception.</Description> <AppDomain>/LM/w3svc/1/ROOT/CopSilverlight.Web-1-129203938565564172</AppDomain> <Exception> <ExceptionType>System.ServiceModel.ProtocolException, System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>There is a problem with the XML that was received from the network. See inner exception for more details.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString>System.ServiceModel.ProtocolException: There is a problem with the XML that was received from the network. See inner exception for more details. ---&gt; System.Xml.XmlException: The body of the message cannot be read because it is empty. --- End of inner exception stack trace ---</ExceptionString> <InnerException> <ExceptionType>System.Xml.XmlException, System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>The body of the message cannot be read because it is empty.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString>System.Xml.XmlException: The body of the message cannot be read because it is empty.</ExceptionString> </InnerException> </Exception> </TraceRecord> </DataItem> </TraceData> </ApplicationData> </E2ETraceEvent>

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  • Long-running ASP.NET tasks

    - by John Leidegren
    I know there's a bunch of APIs out there that do this, but I also know that the hosting environment (being ASP.NET) puts restrictions on what you can reliably do in a separate thread. I could be completely wrong, so please correct me if I am, this is however what I think I know. A request typically timeouts after 120 seconds (this is configurable) but eventually the ASP.NET runtime will kill a request that's taking too long to complete. The hosting environment, typically IIS, employs process recycling and can at any point decide to recycle your app. When this happens all threads are aborted and the app restarts. I'm however not sure how aggressive it is, it would be kind of stupid to assume that it would abort a normal ongoing HTTP request but I would expect it to abort a thread because it doesn't know anything about the unit of work of a thread. If you had to create a programming model that easily and reliably and theoretically put a long running task, that would have to run for days, how would you accomplish this from within an ASP.NET application? The following are my thoughts on the issue: I've been thinking a long the line of hosting a WCF service in a win32 service. And talk to the service through WCF. This is however not very practical, because the only reason I would choose to do so, is to send tasks (units of work) from several different web apps. I'd then eventually ask the service for status updates and act accordingly. My biggest concern with this is that it would NOT be a particular great experience if I had to deploy every task to the service for it to be able to execute some instructions. There's also this issue of input, how would I feed this service with data if I had a large data set and needed to chew through it? What I typically do right now is this SELECT TOP 10 * FROM WorkItem WITH (ROWLOCK, UPDLOCK, READPAST) WHERE WorkCompleted IS NULL It allows me to use a SQL Server database as a work queue and periodically poll the database with this query for work. If the work item completed with success, I mark it as done and proceed until there's nothing more to do. What I don't like is that I could theoretically be interrupted at any point and if I'm in-between success and marking it as done, I could end up processing the same work item twice. I might be a bit paranoid and this might be all fine but as I understand it there's no guarantee that that won't happen... I know there's been similar questions on SO before but non really answers with a definitive answer. This is a really common thing, yet the ASP.NET hosting environment is ill equipped to handle long-running work. Please share your thoughts.

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  • Silverlight Async Timeout Error

    - by Nath
    Calling through to my Silverlight Enabled WCF-Service in my silverlight application, occasionally users get timeouts. Whats the easiest way to boost the time allowed by the service client for a response? The exact exception thrown is: System.TimeoutException: [HttpRequestTimedOutWithoutDetail] Thanks

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  • Async friendly DispatcherTimer wrapper/subclass

    - by Simon_Weaver
    I have a DispatcherTimer running in my code that fire every 30 seconds to update system status from the server. The timer fires in the client even if I'm debugging my server code so if I've been debugging for 5 minutes I may end up with a dozen timeouts in the client. Finally decided I needed to fix this so looking to make a more async / await friendly DispatcherTimer. Code running in DispatcherTimer must be configurable whether it is reentrant or not (i.e. if the task is already running it should not try to run it again) Should be task based (whether or not this requires I actually expose Task at the root is a gray area) Should be able to run async code and await on tasks to complete Whether it wraps or extends DispatcherTimer probably doesn't really matter but wrapping it may be slightly less ambiguous if you don't know how to use it Possibly expose bindable properties for IsRunning for UI

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  • Suggestions for doing async I/O with Task Parallel Library

    - by anelson
    I have some high performance file transfer code which I wrote in C# using the Async Programming Model (APM) idiom (eg, BeginRead/EndRead). This code reads a file from a local disk and writes it to a socket. For best performance on modern hardware, it's important to keep more than one outstanding I/O operation in flight whenever possible. Thus, I post several BeginRead operations on the file, then when one completes, I call a BeginSend on the socket, and when that completes I do another BeginRead on the file. The details are a bit more complicated than that but at the high level that's the idea. I've got the APM-based code working, but it's very hard to follow and probably has subtle concurrency bugs. I'd love to use TPL for this instead. I figured Task.Factory.FromAsync would just about do it, but there's a catch. All of the I/O samples I've seen (most particularly the StreamExtensions class in the Parallel Extensions Extras) assume one read followed by one write. This won't perform the way I need. I can't use something simple like Parallel.ForEach or the Extras extension Task.Factory.Iterate because the async I/O tasks don't spend much time on a worker thread, so Parallel just starts up another task, resulting in potentially dozens or hundreds of pending I/O operations; way too much! You can work around that by Waiting on your tasks, but that causes creation of an event handle (a kernel object), and a blocking wait on a task wait handle, which ties up a worker thread. My APM-based implementation avoids both of those things. I've been playing around with different ways to keep multiple read/write operations in flight, and I've managed to do so using continuations that call a method that creates another task, but it feels awkward, and definitely doesn't feel like idiomatic TPL. Has anyone else grappled with an issue like this with the TPL? Any suggestions?

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  • Silverlight async calls and anonymous methods....

    - by JLewis
    I know there are a couple of debates on this kind of thing.... At any rate, I have several cases where I need to populate combobox items based on enumerations returned from the WCF service. In an effort to keep code clean, I started this approach. After looking into it more, I don't think the this works as well is initially thought... I am throwing this out to get recommendations/advice/code snippets on how you would do this or how you currently do this. I may be forced to have a seperate, non anonymous method, procedure. I hate doing this for something like this but at the moment, don't see it working another way... EventHandler<GetEnumerationsForTypeCompletedEventArgs> ev = null; ev = delegate(object eventSender, GetEnumerationsForTypeCompletedEventArgs eventArgs) { if (eventArgs.Error == null) { //comboBox.ItemsSource = eventArgs.Result; // populate combox for display purposes (for now) foreach (Enumeration e in eventArgs.Result) { ComboBoxItem cbi = new ComboBoxItem(); cbi.Content = e.EnumerationValueDisplayed; comboBox.Items.Add(cbi); } // remove event so we don't keep adding new events each time we need an enumeration proxy.GetEnumerationsForTypeCompleted -= ev; } }; proxy.GetEnumerationsForTypeCompleted += ev; proxy.GetEnumerationsForTypeAsync(sEnumerationType); Basically in this example we use ev to hold the anonymous method so we can then use ev from within the method to remove it from the events once called. This prevents this method from getting called more than one time. I suspect that the comboBox local var declared before this call, but within the same method, is not always the combobox originally intended but can't really verify that yet. I may add a tag to it to do some tests and populating to verify. Sorry if this is not clear. I can elaborate more if needed. Thanks Jeff

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  • Asyncronus javascript rendering widgets

    - by Joe J
    Hey all, I'm creating a javascript widget so third partys (web designers) can post a link on their website and it will render the widget on their site. Currently, I'm doing this with just a script link tag: <div class="some_random_div_in_html_body"> <script type='text/javascript' src='http://remotehost.com/link/to/widget.js'></script> </div> However, this has the side-effect of slowing down a thrid party's website render times of the page if my site is under a load. Therefore, I'd like the third party website to request the widget link from my site asyncronously and then render it on their site when the widget link loads completely. The Google Analytics javascript snippet seems to have a nice bit of asyncronous code that does a nice async request to model off of, but I'm wondering if I can modify it so that it will render content on the third party's site. Using the example below, I want the content of http://mysite.com/link/to/widget.js to render something in the "message" id field. <HTML> <HEAD><TITLE>Third Party Site</TITLE><STYLE>#message { background-color: #eee; } </STYLE></HEAD> <BODY> <div id="message">asdf</div> <script type="text/javascript"> (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = 'http://mysite.com/link/to/widget.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script> </BODY> </HTML> I don't know if what I'm trying to do constitutes Cross Site Scripting (still a bit vague on that concept) but am wondering if what I'm trying to do is possible. Or if anyone has any other approaches to creating javascript widgets effectively, I'd appreciate any advice. Thanks for reading this. Joe

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  • Understanding the Silverlight Dispatcher

    - by Matt
    I had a Invalid Cross Thread access issue, but a little research and I managed to fix it by using the Dispatcher. Now in my app I have objects with lazy loading. I'd make an Async call using WCF and as usual I use the Dispatcher to update my objects DataContext, however it didn't work for this scenario. I did however find a solution here. Here's what I don't understand. In my UserControl I have code to call an Toggle method on my object. The call to this method is within a Dispatcher like so. Dispatcher.BeginInvoke( () => _CurrentPin.ToggleInfoPanel() ); As I mentioned before this was not enough to satisfy Silverlight. I had to make another Dispatcher call within my object. My object is NOT a UIElement, but a simple class that handles all its own loading/saving. So the problem was fixed by calling Deployment.Current.Dispatcher.BeginInvoke( () => dataContext.Detail = detail ); within my class. Why did I have to call the Dispatcher twice to achieve this? Shouldn't a high-level call be enough? Is there a difference between the Deployment.Current.Dispatcher and the Dispatcher in a UIElement?

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  • Async Load JavaScript Files with Callback

    - by Gcoop
    Hi All, I am trying to write an ultra simple solution to load a bunch of JS files asynchronously. I have the following script below so far. However the callback is sometimes called when the scripts aren't actually loaded which causes a variable not found error. If I refresh the page sometimes it just works because I guess the files are coming straight from the cache and thus are there quicker than the callback is called, it's very strange? var Loader = function () { } Loader.prototype = { require: function (scripts, callback) { this.loadCount = 0; this.totalRequired = scripts.length; this.callback = callback; for (var i = 0; i < scripts.length; i++) { this.writeScript(scripts[i]); } }, loaded: function (evt) { this.loadCount++; if (this.loadCount == this.totalRequired && typeof this.callback == 'function') this.callback.call(); }, writeScript: function (src) { var self = this; var s = document.createElement('script'); s.type = "text/javascript"; s.async = true; s.src = src; s.addEventListener('load', function (e) { self.loaded(e); }, false); var head = document.getElementsByTagName('head')[0]; head.appendChild(s); } } Is there anyway to test that a JS file is completely loaded, without putting something in the actual JS file it's self, because I would like to use the same pattern to load libraries out of my control (GMaps etc). Invoking code, just before the tag. var l = new Loader(); l.require([ "ext2.js", "ext1.js"], function() { var config = new MSW.Config(); Refraction.Application().run(MSW.ViewMapper, config); console.log('All Scripts Loaded'); }); Thanks for any help.

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  • Boost asio async vs blocking reads, udp speed/quality

    - by Dolphin
    I have a quick and dirty proof of concept app that I wrote in C# that reads high data rate multicast UDP packets from the network. For various reasons the full implementation will be written in C++ and I am considering using boost asio. The C# version used a thread to receive the data using blocking reads. I had some problems with dropped packets if the computer was heavily loaded (generally with processing those packets in another thread). What I would like to know is if the async read operations in boost (which use overlapped io in windows) will help ensure that I receive the packets and/or reduce the cpu time needed to receive the packets. The single thread doing blocking reads is pretty straightforward, using the async reads seems like a step up in complexity, but I think it would be worth it if it provided higher performance or dropped fewer packets on a heavily loaded system. Currently the data rate should be no higher than 60Mb/s.

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  • HttpRequest.BeginWebRequest not executing asynchronously

    - by Shawn Simon
    I have the following code: Private Function CreateRequest() As HttpWebRequest Dim request As HttpWebRequest = HttpWebRequest.Create(_url) request.Method = "POST" request.ContentType = "application/x-www-form-urlencoded" Dim postData As String = String.Join("&", GetPostData().Select(Function(s) String.Format("{0}={1}", s.Key, HttpUtility.UrlEncode(s.Value))).ToArray) Dim data As Byte() = (New ASCIIEncoding).GetBytes(postData) request.Timeout = _maxTimeoutSeconds * 1000 Dim stream = request.GetRequestStream stream.Write(data, 0, data.Length) stream.Close() Return request End Function Public Sub SendAsync(ByVal callback As Action(Of ResponseBase)) Dim request = CreateRequest() _attemptCount += 1 Dim reqID As Integer If _loggingContext IsNot Nothing Then Try reqID = Log.NotesRequest(_url.ToString, GetPostData, _loggingContext) Catch ex As Exception ErrorTracker.LogError(ex) End Try End If Dim responseState As New ResponseState responseState.LoggedNotesRequestID = reqID responseState.Request = request responseState.Callback = callback Dim response = request.BeginGetResponse(New AsyncCallback(AddressOf RespCallback), responseState) End Sub Private Sub RespCallback(ByVal ar As IAsyncResult) Dim responseState As ResponseState = CType(ar.AsyncState, ResponseState) ' Process response... I set up the request to go to a mock server which sleeps for 30 seconds. When I call BeginGetResponse, the application just waits at that line of code for the response. I want it to carry on with the app, and then just run the callback whenever it finishes. This code is run from a web page, and my callback just logs the response and sends an email. I don't want to use to have to wait for the response.

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