On 24 Oct 2009, at 00:02, paulC wrote:
On Oct 23, 3:18 am, Brian Quinlan <br...@sweetapp.com> wrote:
My test reduction:
import multiprocessing
import queue
def _process_worker(q):
while True:
try:
something = q.get(block=True, timeout=0.1)
except queue.Empty:
return
else:
print('Grabbed item from queue:', something)
def _make_some_processes(q):
processes = []
for _ in range(10):
p = multiprocessing.Process(target=_process_worker,
args=(q,))
p.start()
processes.append(p)
return processes
def _do(i):
print('Run:', i)
q = multiprocessing.Queue()
for j in range(30):
q.put(i*30+j)
processes = _make_some_processes(q)
while not q.empty():
pass
# The deadlock only occurs on Mac OS X and only when these lines
# are commented out:
# for p in processes:
# p.join()
for i in range(100):
_do(i)
--------------
Output (on Mac OS X using the svn version of py3k):
% ~/bin/python3.2 moprocessmoproblems.py
Run: 0
Grabbed item from queue: 0
Grabbed item from queue: 1
Grabbed item from queue: 2
...
Grabbed item from queue: 29
Run: 1
At this point the script produces no additional output. If I
uncomment
the lines above then the script produces the expected output. I don't
see any docs that would explain this problem and I don't know what
the
rule would be e.g. you just join every process that uses a queue
before
the queue is garbage collected.
Any ideas why this is happening?
Cheers,
Brian
I can't promise a definitive answer but looking at the doc.s:-
isAlive()
Return whether the thread is alive.
Roughly, a thread is alive from the moment the start() method
returns until its run() method terminates. The module function
enumerate() returns a list of all alive threads.
I guess that the word 'roughly' indicates that returning from the
start
() call does not mean that all the threads have actually started, and
so calling join is illegal. Try calling isAlive on all the threads
before returning from _make_some_processes.
Regards, Paul C.
--
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Hey Paul,
I guess I was unclear in my explanation - the deadlock only happens
when I *don't* call join.
Cheers,
Brian
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