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POSending arguments to Python threads blocks other threads
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copied!<p>Consider this test application for passing arguments to Python threads:</p> <pre><code>#!/usr/bin/python3 from pprint import pprint import signal import sys import threading class CallThreads(threading.Thread): def __init__(self, target, *args): self._target = target threading.Thread.__init__(self) target(*args) def main(argv): phrases = ['hello', 'goodbye'] num = 0 for phrase in phrases: num += 1 thread_handler = CallThreads(someFunction, phrase, num) thread_handler.daemon = True thread_handler.start() return True def someFunction(a, b): print("Hi: "+str(a)+" and "+str(b)) return True def signal_handler(signal, frame): print(["Got SIGINT!"]) sys.exit(0) if __name__ == '__main__': signal.signal(signal.SIGINT, signal_handler) main(sys.argv) </code></pre> <p>In it's current state, it seems as though the <code>for phrase in phrases</code> loop is waiting for the thread to finish before starting another thread. That is, if <code>someFunction()</code> takes a long time to complete, then the then next thread will not start until the previous thread returns. Why is this, and how can I work around it while still sending arguments to the threads?</p> <p><strong>Edit:</strong> I've tried saving the <code>args</code> array in <code>self._args</code> in the constructor, and then calling <code>self._target(*self._args)</code> or <code>self._target(self._args)</code> in <code>def run (self):</code>. This actually works in Python 2, but not in Python 3. What should I do?</p> <p><strong>Edit:</strong> It seems that the problem is that in Python 3, the <code>run</code> method cannot access the private variables. That is, for the following improved code:</p> <pre><code>def __init__(self, target, *args): self._args = args threading.Thread.__init__(self) def run(self): someFunction(*self._args) </code></pre> <p>Note the following output:</p> <pre><code>Exception in thread Thread-1: Traceback (most recent call last): File "/usr/lib/python3.3/threading.py", line 639, in _bootstrap_inner self.run() File "./test.py", line 19, in run someFunction(*self._args) TypeError: someFunction() missing 2 required positional arguments: 'a' and 'b' </code></pre> <p>And adding a <code>pprint(self._args)</code> to the <code>run()</code> method indeed shows that the tuple returned is empty. However, changing the variables to non-private works! The following code runs fine:</p> <pre><code>def __init__(self, target, *args): self.target = target self.args = args threading.Thread.__init__(self) def run(self): self.target(*self.args) </code></pre> <p>Therefore, I can use the application with public variables in Python 3. <strong>However, is there any way to use private variables in the <code>CallThreads</code> class, as in Python 2?</strong></p> <p>Thanks!</p>

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