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POasync/await thread transition curiosity
 

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    <p>I have the following simple console application:</p> <pre class="lang-cs prettyprint-override"><code>class Program { private static int times = 0; static void Main(string[] args) { Console.WriteLine("Start {0}", Thread.CurrentThread.ManagedThreadId); var task = DoSomething(); task.Wait(); Console.WriteLine("End {0}", Thread.CurrentThread.ManagedThreadId); Console.ReadLine(); } static async Task&lt;bool&gt; DoSomething() { times++; if (times &gt;= 3) { return true; } Console.WriteLine("DoSomething-1 sleeping {0}", Thread.CurrentThread.ManagedThreadId); await Task.Run(() =&gt; { Console.WriteLine("DoSomething-1 sleep {0}", Thread.CurrentThread.ManagedThreadId); Task.Yield(); }); Console.WriteLine("DoSomething-1 awake {0}", Thread.CurrentThread.ManagedThreadId); Console.WriteLine("DoSomething-2 sleeping {0}", Thread.CurrentThread.ManagedThreadId); await Task.Run(() =&gt; { Console.WriteLine("DoSomething-2 sleep {0}", Thread.CurrentThread.ManagedThreadId); Task.Yield(); }); Console.WriteLine("DoSomething-2 awake {0}", Thread.CurrentThread.ManagedThreadId); bool b = await DoSomething(); return b; } } </code></pre> <p>with the output</p> <pre><code>Start 1 DoSomething-1 sleeping 1 DoSomething-1 sleep 3 DoSomething-1 awake 4 DoSomething-2 sleeping 4 DoSomething-2 sleep 4 DoSomething-2 awake 4 DoSomething-1 sleeping 4 DoSomething-1 sleep 3 DoSomething-1 awake 3 DoSomething-2 sleeping 3 DoSomething-2 sleep 3 DoSomething-2 awake 3 End 1 </code></pre> <p>I'm aware that console apps don't provide a SynchronizationContext so Tasks run on the thread pool. But what surprises me is that when resuming execution from an await in <code>DoSomething</code>, we are on the same thread as we are on inside the await. I had assumed that we'd either return to the thread we awaited on or be on another thread entirely when we resume execution of the awaiting method.</p> <p>Does anyone know why? Is my example flawed in some way?</p>
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