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    <p>The interpreter will switch from one thread to another periodically anyway without your intervention - you don't need to tell the system not to 'hog' a thread.</p> <p>However, under normal circumstances, only one Python thread is executing at any one time. (Exceptions tend to revolve around times when threads are waiting on input from external devices such as the hard disk or the network.) This is due to the <a href="http://en.wikipedia.org/wiki/Global_Interpreter_Lock" rel="nofollow noreferrer">Global Interpreter Lock</a>. This does mean however that you probably aren't getting as much benefit from threads in Python as you would in Java or many other languages. Getting around this problem is not necessarily trivial, although moving to <a href="http://docs.python.org/library/multiprocessing.html" rel="nofollow noreferrer">multiprocessing</a> instead of multithreading is one good approach, if possible.</p> <p>However, what you want to do seems flawed in some sense - if you have 2 threads and they both have work to do, you shouldn't have to write application-side code to switch between them. That's the job of the operating system or the virtual machine. If you find yourself telling one thread to 'do less' because you want to favour another thread in terms of processor time, then rather than adding arbitrary yielding or sleeping, you should probably be setting thread priorities instead. (Although again, this may not have much meaning in Python given the presence of the Global Interpreter Lock.)</p>
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    1. POIn there something similar to Java's Thread.yield() in Python? Does that even make sense?
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    1. USKylotan
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    1. POIn there something similar to Java's Thread.yield() in Python? Does that even make sense?
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    1. COWhat happens when a thread is not yielding, is that it starts to starve the other threads. Java and C (pthreads) have yielding functions to tell the scheduler that the thread is "free". The answer here: http://stackoverflow.com/questions/787803/how-does-a-threading-thread-yield-the-rest-of-its-quantum-in-python/787810#787810 seems to give some further insight, but it seems that I can not get around it.
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    2. COI think you are misunderstanding how threads work on most systems. The system will switch between threads automatically on a very regular basis so all threads get to run. (This is called 'pre-emption' or 'preemptive multitasking'.) You don't need to manually switch between them on Java or Python. Methods such as yield() on such systems are a minor optimisation, not a requirement.
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    3. CONo, no. I know about pre-emption. The `yield` I am referring to (in the case of Java or pthreads) is simply advising the scheduler. It is a way to suggest a pre-emption point. As you say it is an optimization. I need to go and read more about the GIL. Thanks.
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