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    <blockquote> <p>From what I understand, the await keyword will suspend the code flow until the function returns</p> </blockquote> <p>Well, Yes and No.</p> <ul> <li>Yes, because code flow does stop in a sense.</li> <li>No, because the thread executing this code flow does not block. (The synchronous call <code>client.GetString()</code> will block the thread).</li> </ul> <p>In fact, it will return to its calling method. To understand what it means by return to its calling method, you can read about another C# compiler magic - the <code>yield return</code> statement.</p> <p>Iterator blocks with <code>yield return</code> will break the method into a state machine - where code after the <code>yield return</code> statement will execute only after <code>MoveNext()</code> is called on the enumerator. (See <a href="http://startbigthinksmall.wordpress.com/2008/06/09/behind-the-scenes-of-the-c-yield-keyword/" rel="noreferrer">this</a> and <a href="http://csharpindepth.com/articles/chapter6/iteratorblockimplementation.aspx" rel="noreferrer">this</a>).</p> <p>Now, <code>async/await</code> mechanism is also based on similar state machine (however, its much more complicated than the <code>yield return</code> state machine).</p> <p>To simplify matters, lets consider a simple async method:</p> <pre><code>public async Task MyMethodAsync() { // code block 1 - code before await // await stateement var r = await SomeAwaitableMethodAsync(); // code block 2 - code after await } </code></pre> <ul> <li>When you mark a method with <code>async</code> identifier you tell the compiler to break the method into a state machine and that you are going to <code>await</code> inside this method.</li> <li>Lets say code is running on a thread <code>Thread1</code> and your code calls this <code>MyMethodAsync()</code>. Then <code>code block 1</code> will synchronously run on the same thread. </li> <li><code>SomeAwaitableMethodAsync()</code> will also be called synchronously - but lets say that method starts a new asynchronous operation and returns a <code>Task</code>. </li> <li>This is when <code>await</code> comes into picture. It will return the code flow back to its caller and the thread <code>Thread1</code> is free to run callers code. What happens then in calling method depends on whether calling method <code>await</code>s on <code>MyMethodAsync()</code> or does something else - but important thing is <code>Thread1</code> is not blocked.</li> <li>Now rest of await's magic - When the Task returned by <code>SomeAwaitableMethodAsync()</code> eventually completes, the <code>code block 2</code> is <em>Scheduled</em> to run.</li> <li><code>async/await</code> is built on the Task parallel library - so, this <em>Scheduling</em> is done over TPL.</li> <li>Now the thing is that this <code>code block 2</code> may not be scheduled over the same thread <code>Thread1</code> unless it had an active <code>SynchronizationContext</code> with thread affinity (like WPF/WinForms UI thread). <code>await</code> is <code>SynchronizationContext</code> aware, so, <code>code block 2</code> is scheduled over same <code>SynchronizationContext</code>, if any, when the <code>MyMethodAsync()</code> was called. If there was no active <code>SynchronizationContext</code>, then with all possibility, <code>code block 2</code> will run over some different thread.</li> </ul> <p>Lastly, I will say that since <code>async/await</code> is based on state machine created by compiler, like <code>yield return</code>, it shares some of the shortcomings - for example, you cannot <code>await</code> inside a <code>finally</code> block.</p> <p>I hope this clears your doubts.</p>
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    1. POHow is async w/ await different from a synchronous call?
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    1. COThanks for the elaborate answer!
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