New submission from Mark Dickinson:
On OS X (10.9.5), I'm getting an apparent deadlock in the following simple
Python script:
#--------------------------------------------------------
import itertools
import threading
def is_prime(n):
return n >= 2 and all(n % d for d in xrange(2, n))
def count_primes_in_range(start, stop):
return sum(is_prime(n) for n in xrange(start, stop))
def main():
threads = [
threading.Thread(
target=count_primes_in_range,
args=(12500*i, 12500*(i+1))
)
for i in xrange(8)
]
for thread in threads:
thread.start()
for thread in threads:
thread.join()
if __name__ == '__main__':
for i in itertools.count():
print "Iteration: ", i
main()
#--------------------------------------------------------
Each iteration takes around 60 seconds, and I typically get a deadlock within
the first 5 iterations. It looks as though the deadlock happens during the
"thread.join", at a stage where some of the threads have already completed and
been joined. The code hangs with no CPU activity, and a backtrace (attached)
shows that all the background threads are waiting for the GIL, while the main
thread is in a blocking `thread.join` call.
I've attached a gdb-generated stack trace.
I was unable to reproduce this with a debug build of Python. I *have*
reproduced with a normal build of Python, and on various Python 2.7 executables
from 3rd party sources (Apple, Macports, Enthought Canopy).
I've also not yet managed to reproduce on Python 3, but I haven't tried that
hard. I suspect it's a Python 2-only problem, though.
(And yes, this is horrible code that doesn't make much sense. It's actually a
cut-down example from a "how not to do it" part of a course on concurrency.
Nevertheless, it shouldn't be deadlocking.)
----------
components: Interpreter Core
files: hang_backtrace.txt
messages: 260273
nosy: mark.dickinson
priority: normal
severity: normal
status: open
title: Deadlock in thread.join
type: behavior
versions: Python 2.7
Added file: http://bugs.python.org/file41920/hang_backtrace.txt
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue26360>
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