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copied!<p>Your vendor would be right if yours was <strong>pure python</strong> code; however, C extensions may release the <a href="http://effbot.org/pyfaq/what-is-the-global-interpreter-lock.htm" rel="nofollow noreferrer">GIL</a>, and therefore allows for actual multithreading.</p> <p>In particular, time.sleep <strong>does</strong> release the GIL (you can check it directly from the source code, <a href="http://svn.python.org/view/python/trunk/Modules/timemodule.c?view=markup" rel="nofollow noreferrer">here</a> - look at <code>floatsleep</code> implementation); so your code should not have any problem. As a further proof, I have made also a simple test, just removing the calls to USB, and it actually works as expected:</p> <pre><code>from threading import Thread import time import sys usb_device = 0 def usb_dump(): for i in range(100): time.sleep(0.001) print "dumping usb" class DumpThread(Thread): def run(self): usb_dump() t = DumpThread() t.start() print "Sleep 1" time.sleep(1) print "End" sys.exit(0) </code></pre> <p>Finally, just a couple of notes on the code you posted:</p> <ul> <li>usb_device is not being passed to the thread. You need to pass it as a parameter or (argh!) tell the thread to get it from the global namespace.</li> <li>Instead of forcing sys.exit(), it could be better to just signal the thread to stop, and then closing USB device. I suspect your code could get some multithreading issue, as it is now.</li> <li>If you need just a periodic poll, threading.Timer class may be a better solution for you.</li> </ul> <p>[<em>Update</em>] About the latest point: as told in the comment, I think a <code>Timer</code> would better fit the semantic of your function (a periodic poll) and would automatically avoid issues with the GIL not being released by the vendor code.</p>

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