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POLaunching multiple tasks from a WCF service
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copied!<p>I need to optimize a WCF service... it's quite a complex thing. My problem this time has to do with tasks (Task Parallel Library, .NET 4.0). What happens is that I launch several tasks when the service is invoked (using <code>Task.Factory.StartNew</code>) and then wait for them to finish:</p> <pre><code>Task.WaitAll(task1, task2, task3, task4, task5, task6); </code></pre> <p>Ok... what I see, and don't like, is that on the first call (sometimes the first 2-3 calls, if made quickly one after another), the final task starts much later than the others (I am looking at a case where it started 0.5 seconds after the others). I tried calling</p> <pre><code>ThreadPool.SetMinThreads(12*Environment.ProcessorCount, 20); </code></pre> <p>at the beginning of my service, but it doesn't seem to help.</p> <p>The tasks are all database-related: I'm reading from multiple databases and it has to take as little time as possible.</p> <p>Any idea why the last task is taking so long? Is there something I can do about it?</p> <p>Alternatively, should I use the thread pool directly? As it happens, in one case I'm looking at, one task had already ended before the last one started - I would had saved 0.2 seconds if I had reused that thread instead of waiting for a new one to be created. However, I can not be sure that <em>that</em> task will always end so quickly, so I can't put both requests in the same task.</p> <p>[Edit] The OS is Windows Server 2003, so there should be no connection limit. Also, it is hosted in IIS - I don't know if I should create regular threads or using the thread pool - which is the preferred version?</p> <p>[Edit] I've also tried using <code>Task.Factory.StartNew(action, TaskCreationOptions.LongRunning);</code> - it doesn't help, the last task still starts much later (around half a second later) than the rest.</p> <p>[Edit] MSDN<a href="http://msdn.microsoft.com/en-us/library/0ka9477y(v=vs.85).aspx" rel="noreferrer">1</a> says:</p> <blockquote> <p>The thread pool has a built-in delay (half a second in the .NET Framework version 2.0) before starting new idle threads. If your application periodically starts many tasks in a short time, a small increase in the number of idle threads can produce a significant increase in throughput. Setting the number of idle threads too high consumes system resources needlessly.</p> </blockquote> <p>However, as I said, I'm already calling SetMinThreads and it doesn't help.</p>

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