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    <p>Unfortunately, this can't be solved with a <code>TaskScheduler</code>, because they always work at the <code>Task</code> level, and an <code>async</code> method almost always contains multiple <code>Task</code>s.</p> <p>You should use a <a href="http://msdn.microsoft.com/en-us/library/system.threading.semaphoreslim.aspx" rel="nofollow"><code>SemaphoreSlim</code></a> in conjunction with a prioritizing scheduler. Alternatively, you could use <a href="http://blogs.msdn.com/b/pfxteam/archive/2012/02/12/10266988.aspx" rel="nofollow"><code>AsyncLock</code></a> (which is also included in my <a href="http://nitoasyncex.codeplex.com/" rel="nofollow">AsyncEx library</a>).</p> <pre><code>class Program { private static QueuedTaskScheduler queueScheduler = new QueuedTaskScheduler(targetScheduler: TaskScheduler.Default, maxConcurrencyLevel: 1); private static TaskScheduler ts_priority1; private static TaskScheduler ts_priority2; private static SemaphoreSlim semaphore = new SemaphoreSlim(1); static void Main(string[] args) { ts_priority1 = queueScheduler.ActivateNewQueue(1); ts_priority2 = queueScheduler.ActivateNewQueue(2); QueueValue(1, ts_priority2); QueueValue(2, ts_priority2); QueueValue(3, ts_priority2); QueueValue(4, ts_priority1); QueueValue(5, ts_priority1); QueueValue(6, ts_priority1); Console.ReadLine(); } private static Task QueueTask(Func&lt;Task&gt; f, TaskScheduler ts) { return Task.Factory.StartNew(f, CancellationToken.None, TaskCreationOptions.HideScheduler | TaskCreationOptions.DenyChildAttach, ts).Unwrap(); } private static Task QueueValue(int i, TaskScheduler ts) { return QueueTask(async () =&gt; { await semaphore.WaitAsync(); try { Console.WriteLine("Start {0}", i); await Task.Delay(1000); Console.WriteLine("End {0}", i); } finally { semaphore.Release(); } }, ts); } } </code></pre>
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    1. POLimited concurrency level task scheduler (with task priority) handling wrapped tasks
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    1. USStephen Cleary
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    1. COThis looks like an interesting solution. However, I see one problem with this. Although the solution will (at first) result in the correct output (as in this question), but it will break the priority of the executed tasks. The scheduler will execute all tasks (in the correct priority) up until the `await semaphore.WaitAsync()` but tasks with higher priority will not be released from the lock before tasks of lower priority. This is especially true if higher priority tasks are scheduled after lower priority tasks (that are still waiting to be released from the lock).
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    2. COIn that case, you'll need an actual priority-based lock, which does not exist because AFAIK no one else has needed one. You'll have to build your own.
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    3. COI have added my own [answer](http://stackoverflow.com/a/13414364/1514235). Please have a look and see what you think.
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