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copied!<p>Yes, this code is wrong - the outcome is not really defined, but it would be quite reasonable for it to throw an exception at the <code>mrEvent.WaitOne()</code>, since <code>mrEvent</code> is the almost-certainly-now-disposed <code>ManualResetEvent</code>. Technically there's a chance that the worker thread was all ready to go, and the worker thread did its "some processing..." faster than the primary thread did the "some other processing...", but: I wouldn't rely on it. So in most cases: <code>mrEvent</code> is dead already.</p> <p>As for how to avoid this: perhaps this simply isn't a scenario for <code>using</code>. But it occurs that since the worker thread does a <code>WaitOne</code>, the worker thread's <code>WaitOne</code> <strong>cannot</strong> complete before the primary thread performs the <code>mre.Set()</code> call - so you could exploit that and move the <code>using</code> to the worker:</p> <pre><code> var mre = new ManualResetEvent(false); var bgWkr = new BackgroundWorker(); bgWkr.DoWork += delegate(object sender, DoWorkEventArgs e) { using(var mrEvent = e.Argument as ManualResetEvent) { // some processing... mrEvent.WaitOne(); } // broadcast an event }; bgWkr.RunWorkerAsync(mre); // some other processing... // hook into the same event mre.Set(); </code></pre> <p>Note, however, that this raises an interesting question of what happens if the primary thread throws an exception in the "some other processing..." - the call to <code>mre.Set()</code> would never be reached, and the worker thread would never exit. You might want to do the <code>mre.Set()</code> in a <code>finally</code>:</p> <pre><code> var mre = new ManualResetEvent(false); try { var bgWkr = new BackgroundWorker(); bgWkr.DoWork += delegate(object sender, DoWorkEventArgs e) { using(var mrEvent = e.Argument as ManualResetEvent) { // some processing... mrEvent.WaitOne(); } // broadcast an event }; bgWkr.RunWorkerAsync(mre); // some other processing... } finally { // hook into the same event mre.Set(); } </code></pre>

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