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POProblem with IHttpAsyncHandler and ASP.NET "Requests Executing" counter
 

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  1. POProblem with IHttpAsyncHandler and ASP.NET "Requests Executing" counter
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    <p><h1>Solved:</h1><b>I found the solution to this. </b><s>Not sure why it happens but</s><b> Switching the application pool type to 'classic' from 'integrated' solves the problem. Now the 'Requests Executing' keeps going up, the actual application pool process thread remains low (~31 threads) and the app is <em>very</em> responsive (as it should be). <br><br><s>I'm using .Net 2.0 so maybe there is an issue there - tried to google it but no luck.</s> </b> <hr> <b>See <a href="https://stackoverflow.com/questions/6123453/problem-with-ihttpasynchandler-and-asp-net-requests-executing-counter/6128861#6128861">Joe Enzminger's reply for an explanation</a> </b> <hr> Thank you all again. <br/><br/><i>ps. the code is used for playing pool (billiards) online - windows (free) version <a href="http://poolrebel.com" rel="nofollow noreferrer">here</a> for anyone curious and brave enough to try :)</i></p> <hr/> <p>Hello,</p> <p>I've implemented an IHttpAsyncHandler that client applications "poll" to wait for server notifications. Notifications are generated by other "activities" on the server and the Async Handler does no work at all.</p> <p>The execution steps are:</p> <pre><code>IHttpAsyncHandler.BeginProcessRequest Create AsyncResult instance and add it to a "registered clients" collection return the AsyncResult </code></pre> <p><i>...other server activity will generate notifications to be sent to registered clients...</i></p> <pre><code>AsyncResult.CompleteCall called as a result of the generated notification(s). IHttpAsyncHandler.EndProcessRequest is called The notification(s) attached to the AsyncResult are written to the response stream. </code></pre> <p><b>The problem:</b></p> <p>I've tested this on IIS7 on a VM with Windows Server 2008 SP2 and 1 cpu core. After 12 clients register for notifications (using an HTTP GET on the Async.ashx) the performance is degraded to the point that subsequent clients cannot connect.</p> <p>When I check the ASP.NET performance counters the "Requests Executing" counter goes up with each client registration and stays at 12 (which appears to be its maximum value - probably a thread pool size per CPU). </p> <p>I find this very confusing. I though the whole point of async handlers is to free up threads for other connections. It appears that this is not the case so I must be doing something wrong!</p> <p>Why is ASP.NET consuming a thread while waiting for my AsyncResult to complete? Is this a config issue? Do I need to do something specific to indicate that this is an Async Handler?</p> <p>Thank you, Nikos.</p> <p><b>Edit: Added code below:</b><br></p> <pre><code>public class AsyncResult : IAsyncResult { private AsyncCallback _cb; private object _state; private ManualResetEvent _event; private bool _completed; private bool _completedsynchronously; private HttpContext _context; private byte[] _data; private int _datalength; private object _lock = new object(); public AsyncWaitResult(AsyncCallback cb, object state, HttpContext context) { _context = context; _cb = cb; _state = state; } public void Close() { if (_event != null) { _event.Close(); _event = null; } } public HttpContext Context { get { return _context; } } public Object AsyncState { get { return _state; } } public bool CompletedSynchronously { get { return _completedsynchronously; } } public bool IsCompleted { get { return _completed; } } public byte[] Data { get { return _data; } } public int DataLength { get { return _datalength; } } public WaitHandle AsyncWaitHandle { get { lock (_lock) { if (_event == null) _event = new ManualResetEvent(_completed); return _event; } } } public void CompleteCall(byte[] data, int length, bool completedsynchronously) { _data = data; _datalength = length; _completedsynchronously = completedsynchronously; lock (_lock) { _completed = true; if (_event != null) _event.Set(); } if (_cb != null) _cb(this); } } public class Outbound : IHttpAsyncHandler { public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object state) { AsyncResult asyncresult = new AsyncResult(cb, state, context); RegisteredClients.Instance.Add(asyncresult); return asyncresult; } public void EndProcessRequest(IAsyncResult ar) { AsyncResult result = (AsyncResult)ar; if (result != null) { result.Context.Response.Cache.SetCacheability(HttpCacheability.NoCache); result.Context.Response.ContentType = "application/octet-stream"; result.Context.Response.AddHeader("Connection", "keep-alive"); if (result.Data != null) result.Context.Response.OutputStream.Write(result.Data, 0, result.DataLength); result.Close(); } } public void ProcessRequest(HttpContext context){} public bool IsReusable { get { return true; } } } </code></pre>
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    1. COI think you need to post more detailed code. It sounds like a "leak" of some kind as a result of failing to implement the async pattern correctly, but it's hard to say.
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      1. USJoe Enzminger
    2. COdone - pretty simple really. If you want clarifications pls let me know.
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    3. CORegisteredClients.Instance.Add() can't block for any reason, can it?
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