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POHow to wait for a BackgroundWorker to cancel?
 

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  1. POHow to wait for a BackgroundWorker to cancel?
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    <p>Consider a <em>hypothetical</em> method of an object that does stuff for you:</p> <pre><code>public class DoesStuff { BackgroundWorker _worker = new BackgroundWorker(); ... public void CancelDoingStuff() { _worker.CancelAsync(); //todo: Figure out a way to wait for BackgroundWorker to be cancelled. } } </code></pre> <p>How can one wait for a BackgroundWorker to be done?</p> <hr> <p>In the past people have tried:</p> <pre><code>while (_worker.IsBusy) { Sleep(100); } </code></pre> <p>But <a href="http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1819196&amp;SiteID=1" rel="noreferrer">this deadlocks</a>, because <code>IsBusy</code> is not cleared until after the <code>RunWorkerCompleted</code> event is handled, and that event can't get handled until the application goes idle. The application won't go idle until the worker is done. (Plus, it's a busy loop - disgusting.)</p> <p>Others have add suggested kludging it into:</p> <pre><code>while (_worker.IsBusy) { Application.DoEvents(); } </code></pre> <p>The problem with that is that is <code>Application.DoEvents()</code> causes messages currently in the queue to be processed, which cause re-entrancy problems (.NET isn't re-entrant).</p> <p>I would hope to use some solution involving Event synchronization objects, where the code <strong>waits</strong> for an event - that the worker's <code>RunWorkerCompleted</code> event handlers sets. Something like:</p> <pre><code>Event _workerDoneEvent = new WaitHandle(); public void CancelDoingStuff() { _worker.CancelAsync(); _workerDoneEvent.WaitOne(); } private void RunWorkerCompletedEventHandler(sender object, RunWorkerCompletedEventArgs e) { _workerDoneEvent.SetEvent(); } </code></pre> <p>But I'm back to the deadlock: the event handler can't run until the application goes idle, and the application won't go idle because it's waiting for an Event.</p> <p>So how can you wait for an BackgroundWorker to finish?</p> <hr> <p><strong>Update</strong> People seem to be confused by this question. They seem to think that I will be using the BackgroundWorker as:</p> <pre><code>BackgroundWorker worker = new BackgroundWorker(); worker.DoWork += MyWork; worker.RunWorkerAsync(); WaitForWorkerToFinish(worker); </code></pre> <p>That is <em>not</em> it, that is <em>not</em> what I'm doing, and that is <em>not</em> what is being asked here. If that were the case, there would be no point in using a background worker.</p>
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