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    <p>If you're already using Twisted, you should never need to "wait" like this.</p> <p>As you've described it:</p> <blockquote> <p>I spawn a thread to run a long operation ... This long operation also spawns some threads using twisted's deferToThread ...</p> </blockquote> <p>That implies that you're calling <code>deferToThread</code> from your "long operation" thread, not from your main thread (the one where <code>reactor.run()</code> is running). As Jean-Paul Calderone already noted in a comment, you can <em>only</em> call Twisted APIs (such as <code>deferToThread</code>) from the main reactor thread.</p> <p>The lock-up that you're seeing is a common symptom of not following this rule. It has nothing to do with the GIL, and everything to do with the fact that you have put Twisted's reactor into a broken state.</p> <p>Based on your loose description of your program, I've tried to write a sample program that does what you're talking about based entirely on Twisted APIs, spawning all threads via Twisted and controlling them all from the main reactor thread.</p> <pre><code>import time from twisted.internet import reactor from twisted.internet.defer import gatherResults from twisted.internet.threads import deferToThread, blockingCallFromThread def workReallyHard(): "'Work' function, invoked in a thread." time.sleep(0.2) def longOperation(): for x in range(10): workReallyHard() blockingCallFromThread(reactor, startShortOperation, x) result = blockingCallFromThread(reactor, gatherResults, shortOperations) return 'hooray', result def shortOperation(value): workReallyHard() return value * 100 shortOperations = [] def startShortOperation(value): def done(result): print 'Short operation complete!', result return result shortOperations.append( deferToThread(shortOperation, value).addCallback(done)) d = deferToThread(longOperation) def allDone(result): print 'Long operation complete!', result reactor.stop() d.addCallback(allDone) reactor.run() </code></pre> <p>Note that at the point in <code>allDone</code> where the reactor is stopped, you could fire off another "long operation" and have it start the process all over again.</p>
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    1. CO"If you're already using Twisted, you should never need to "wait" like this.". I cant believe nobody mentioned this till now.
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      1. USJeffrey Jose
    2. COThis works well but with a bit of experimentation I found that it is a little more involved then I would like. Seems the operations called using reactor threads block the reactor event loop. I used callInThread and callLater for a simple test. If my callInThread method sleeps for 30 seconds and I have my callLater firing at 10 seconds, I will not get the callLater until AFTER callInThread is complete. Is it possible to have a reactor-safe thread block? Or should I start ripping things apart?
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      1. USCharles
    3. COCharles, I'm sorry, but I don't know what you're talking about. callInThread will call your function in a thread, and not block the reactor mainloop; that's the whole point. I'd need to see a complete, working example of the code you're talking about to be more helpful.
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