Richard Oudkerk added the comment:
On Unix, using the fork start method (which was the only option till 3.4),
every sub process will incref every shared object for which its parent has a
reference.
This is deliberate because there is not really any way to know which shared
objects a subprocess might use. (On Windows where only things pickled as part
of the process object are inherited by the child process, we can know exactly
which shared objects the child process should incref.)
Typical programs will only have a single manager (or a very small number) but
may have a large number of normal processes (which will also do the increfing).
I do not think that this is worth trying to fix, particularly as it can cause
compatibility problems.
For 3.4 you can use the "spawn" or "forkserver" start methods instead.
import multiprocessing, logging
objs = []
def newman(n=50):
m = multiprocessing.Manager()
print('created')
for i in range(n):
objs.append(m.Value('i',i))
return m
def foo():
pass
if __name__ == '__main__':
## Try uncommenting next line with Python 3.4
# multiprocessing.set_start_method('spawn')
multiprocessing.log_to_stderr(logging.DEBUG)
print('#### first man')
m1 = newman()
print('#### starting foo')
p = multiprocessing.Process(target=foo)
p.start()
p.join()
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<http://bugs.python.org/issue20660>
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