> On 5 Dec 2021, at 23:50, Johannes Bauer <dfnsonfsdu...@gmx.de> wrote:
>
> Hi there,
>
> I'm a bit confused. In my scenario I a mixing threading with
> multiprocessing. Threading by itself would be nice, but for GIL reasons
> I need both, unfortunately. I've encountered a weird situation in which
> multiprocessing Process()es which are started in a new thread don't
> actually start and so they deadlock on join.
>
> I've created a minimal example that demonstrates the issue. I'm running
> on x86_64 Linux using Python 3.9.5 (default, May 11 2021, 08:20:37)
> ([GCC 10.3.0] on linux).
>
> Here's the code:
I suggest that you include the threading.current_thread() in your messages.
Then you can see which thread is saying what.
Barry
>
>
> import time
> import multiprocessing
> import threading
>
> def myfnc():
> print("myfnc")
>
> def run(result_queue, callback):
> result = callback()
> result_queue.put(result)
>
> def start(fnc):
> def background_thread():
> queue = multiprocessing.Queue()
> proc = multiprocessing.Process(target = run, args = (queue,
> fnc))
> proc.start()
> print("join?")
> proc.join()
> print("joined.")
> result = queue.get()
> threading.Thread(target = background_thread).start()
>
> start(myfnc)
> start(myfnc)
> start(myfnc)
> start(myfnc)
> while True:
> time.sleep(1)
>
>
> What you'll see is that "join?" and "joined." nondeterministically does
> *not* appear in pairs. For example:
>
> join?
> join?
> myfnc
> myfnc
> join?
> join?
> joined.
> joined.
>
> What's worse is that when this happens and I Ctrl-C out of Python, the
> started Thread is still running in the background:
>
> $ ps ax | grep minimal
> 370167 pts/0 S 0:00 python3 minimal.py
> 370175 pts/2 S+ 0:00 grep minimal
>
> Can someone figure out what is going on there?
>
> Best,
> Johannes
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>
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