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    <p>A "cancel flag" is the way to do it, though not a global one, necessarily. The unavoidable point is that you need <strong>some</strong> way to signal to the thread that it should stop what it's doing.</p> <p>In the case of <code>BeginInvoke</code>, this is hard to do with anything but a global flag, because the work is carried out on the threadpool, and you don't know which thread. You have a couple of options (in order of preference):</p> <ol> <li>Use the <code>BackgroundWorker</code> instead of <code>BeginInvoke</code>. This has <a href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.cancelasync.aspx" rel="nofollow noreferrer">cancellation functionality baked-in</a>. This has other benefits, like <a href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.progresschanged.aspx" rel="nofollow noreferrer">progress monitoring</a>, and <a href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.runworkercompleted.aspx" rel="nofollow noreferrer">"Work complete" callbacks</a>. It also nicely <a href="https://stackoverflow.com/questions/258662/unhandled-exceptions-in-backgroundworker">handles exceptions</a>.</li> <li>Use <code>ThreadPool.QueueUserWorkItem</code>, passing in an object as the state that has a <code>Cancel()</code> method that sets a <code>Cancelled</code> flag that the executing code can check. Of course you'll need to keep a reference to the state object so you can call <code>Cancel()</code> on it (which is something the <code>BackgroundWorker</code> does for you - you have a component on your form. (Thanks to <a href="https://stackoverflow.com/users/93623/fredrik-mork">Fredrik</a> for reminding about this).</li> <li>Create your own <code>ThreadStart</code> delegate, passing in a state object as with option 2.</li> </ol>
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    1. POHow to cancel an asynchronous call?
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    1. USNeil Barnwell
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    1. POHow to cancel an asynchronous call?
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    1. CO+1 - As an addition; the `WaitCallback` used with the `ThreadPool.QueueUserWorkItem` takes a state object parameter, so that can also be used, instead of creating custom ThreadStart delegates.
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      1. USFredrik Mörk
    2. COAhh yes - I will plagarise your QueueUserWorkItem point. It's largely the same, but I have to admit I **always** use TP.QUWI rather than managing threads myself.
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      1. USNeil Barnwell
    3. CO+1: and on the topic of QUWI, it's also much more lightweight as there is(/may be) no need to create the thread if the pool isn't full.
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      1. USSteven Evers
 

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