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    <p>From what I understand you want to constrain the number of threads used for processing a certain type of message at the same time.</p> <p>One approach would be to simply wrap the message processor, invoked on a new thread with something like</p> <pre><code>try { Interlocked.Increment(ref count) Process(message); } finally { Interlocked.Decrement(ref count) } </code></pre> <p>Before invoking the wrapper, simply check if the ‘count’ is less than your threshold count; and stop polling/handling more messages till the count is sufficiently lower.</p> <p><strong>EDIT</strong> Added more information based on comment</p> <p>Frans, not sure why you see the infrastructure and business code being coupled. Once you place your business process to be serviced as a task on a new thread to run asynchronously, you need not worry about performing additional IO bound calls asynchronously. This is a simpler model to program in.</p> <p>Here is what I am thinking.</p> <pre><code>// semi - pseudo-code // Infrastructure – reads messages from the queue // (independent thread, could be a triggered by a timer) while(count &lt; maxCount &amp;&amp; (message = Queue.GetMessage()) != null) { Interlocked.Increment(ref count); // process message asynchronously on a new thread Task.Factory.StartNew(() =&gt; ProcessWrapper(message)); } // glue / semi-infrastructure - deals with message deletion and exceptions void ProcessWrapper(Message message) { try { Process(message); Queue.DeleteMessage(message); } catch(Exception ex) { // Handle exception here. // Log, write to poison message queue etc ... } finally { Interlocked.Decrement(ref count) } } // business process void Process(Message message) { // actual work done here ; } </code></pre>
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    1. POHow to implement an IIS-like threadpool on a worker-server
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    1. COThanks for responding. You are right, limiting how many requests I start to process is easy, using the method you outlined or semaphores. What I can't get my head around is how to deal with the returns from async calls. Unless I explicitly put the thread throttling code directly in my return functions, but that would be putting infrastructure code into business logic so I would prefer not to do it if I can help it.
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    2. COFrans, The way I see it the async call would be self-contained and only throw an exception (to signal it could not process the message successfully). If the message is processed successfully the message can be deleted else the ‘infrastructure’ code can deal with it appropriately (log, move to poison queue etc). Please see my updated answer … it may offer more clarity.
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    3. COThanks again. Your solution would limit the total number of requests I am serving concurrently but would not distinguish between the amount of work required on the worker; A locally CPU intensive request is limited similarly to a request that is I/O bound for 5 seconds. On another note, if you do find yourself implementing something like this, you may want to look at semaphores as an alternative to increasing and decreasing a counter. Thanks again for your help.
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