New submission from Naftali Harris:
Hi everyone,
It appears that if you use a global variable in a function that you pass to
Pool.map, but modify that global variable after instantiating the Pool, then
the modification will not be reflected when Pool.map calls that function.
Here's a short script, (also attached), that demonstrates what I mean:
$ cat reproduces.py
from multiprocessing import Pool
name = "Not Updated"
def f(ignored):
print(name)
def main():
global name
p = Pool(3)
name = "Updated"
p.map(f, range(3))
if __name__ == "__main__":
main()
$ python reproduces.py
Not Updated
Not Updated
Not Updated
If the `name = "Updated"' line is moved above the `p = Pool(3)' line, then the
script will print "Updated" three times instead.
This behavior is present in versions 2.6, 2.7, 3.1, 3.2, 3.3, and 3.4. I run
Linux Mint 14 (nadia), on an Intel i5-3210M processor (four cores).
Is this expected behavior?
Thanks very much,
Naftali
----------
components: Library (Lib)
files: reproduces.py
messages: 212221
nosy: Naftali.Harris
priority: normal
severity: normal
status: open
title: Modifications to global variables ignored after instantiating
multiprocessing.Pool
type: behavior
versions: Python 2.7, Python 3.1, Python 3.2, Python 3.3, Python 3.4
Added file: http://bugs.python.org/file34223/reproduces.py
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<http://bugs.python.org/issue20775>
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