[issue20147] multiprocessing.Queue.get() raises queue.Empty exception if even if an item is available

[Alexei Mozhaev]

Alexei Mozhaev added the comment:

We have a similar bug with Queue.get().

Queue.get(False) raises an exception Queue.Empty in the case when the queue is actually not empty!

An example of the code is attached and is listed below just in case:

----------------------
import multiprocessing
import Queue

class TestWorker(multiprocessing.Process):

    def __init__(self, inQueue):
        multiprocessing.Process.__init__(self)
        self.inQueue = inQueue

    def run(self):
        while True:
            try:
                task = self.inQueue.get(False)
            except Queue.Empty:
                # I suppose that Queue.Empty exception is about empty queue 
                # and self.inQueue.empty() must be true in this case
                # try to check it using assert
                assert self.inQueue.empty()
                break


def runTest():
    queue = multiprocessing.Queue()
    for _ in xrange(10**5):
        queue.put(1)
    workers = [TestWorker(queue) for _ in xrange(4)]
    map(lambda w: w.start(), workers)
    map(lambda w: w.join(), workers)


if __name__ == "__main__":
    runTest()
----------------------

----------
nosy: +Alexei.Mozhaev
versions:  -Python 3.1, Python 3.2, Python 3.3, Python 3.4, Python 3.5
Added file: http://bugs.python.org/file35000/py_mult_queue_bug.py

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20147>
_______________________________________