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POWhy does the Task Parallel Library have a 'hidden' 1 second timeout for scheduling tasks under certain conditions?
 

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  1. POWhy does the Task Parallel Library have a 'hidden' 1 second timeout for scheduling tasks under certain conditions?
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    <p>My laptop has 2 logical processors and I stumbled upon the scenario where if I schedule 2 tasks that take longer than 1 second without designating them long-running, subsequent tasks are started after 1 second has elapsed. It is possible to change this timeout?</p> <p>I know normal tasks should be short-running - much shorter than a second if possible - I'm just wondering I am seeing hard-coded TPL behavior or if I can influence this behavior in any way other than designating tasks long-running.</p> <p>This Console app method should demonstrate the behavior for a machine with any number of processors:</p> <pre><code>static void Main(string[] args) { var timer = new Stopwatch(); timer.Start(); int numberOfTasks = Environment.ProcessorCount; var rudeTasks = new List&lt;Task&gt;(); var shortTasks = new List&lt;Task&gt;(); for (int index = 0; index &lt; numberOfTasks; index++) { int capturedIndex = index; rudeTasks.Add(Task.Factory.StartNew(() =&gt; { Console.WriteLine("Starting rude task {0} at {1}ms", capturedIndex, timer.ElapsedMilliseconds); Thread.Sleep(5000); })); } for (int index = 0; index &lt; numberOfTasks; index++) { int capturedIndex = index; shortTasks.Add(Task.Factory.StartNew(() =&gt; { Console.WriteLine("Short-running task {0} running at {1}ms", capturedIndex, timer.ElapsedMilliseconds); })); } Task.WaitAll(shortTasks.ToArray()); Console.WriteLine("Finished waiting for short tasks at {0}ms", timer.ElapsedMilliseconds); Task.WaitAll(rudeTasks.ToArray()); Console.WriteLine("Finished waiting for rude tasks at {0}ms", timer.ElapsedMilliseconds); Console.ReadLine(); } </code></pre> <p>Here is the app's output on my 2 proc laptop:</p> <pre><code>Starting rude task 0 at 2ms Starting rude task 1 at 2ms Short-running task 0 running at 1002ms Short-running task 1 running at 1002ms Finished waiting for short tasks at 1002ms Finished waiting for rude tasks at 5004ms Press any key to continue . . . </code></pre> <p>The lines:</p> <pre><code>Short-running task 0 running at 1002ms Short-running task 1 running at 1002ms </code></pre> <p>indicate that there is a 1 second timeout or something of that nature allowing the shorter-running tasks to get scheduled over the 'rude' tasks. That's what I'm inquiring about.</p>
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      1. POWhy does the Task Parallel Library have a 'hidden' 1 second timeout for scheduling tasks under certain conditions?
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    2. VO
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    1. COPlease post a description of the misbehavior.
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      1. POWhy does the Task Parallel Library have a 'hidden' 1 second timeout for scheduling tasks under certain conditions?
      1. USAdam Robinson
    2. CO@AdamRobinson Hi Adam, the first paragraph describes the behavior I am seeing - I am uncertain if I should call it "misbehavior" but I would like to know if I can affect this behavior in any way, or if I need to adjust my expectations and approach to using the TPL
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    3. COSorry, I meant some sample output demonstrating what you're describing. I'm not exactly clear what it is you're describing, but seeing your console output might make that clearer.
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      1. USAdam Robinson
 

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