[issue11382] some posix module functions unnecessarily release the GIL

[Charles-Francois Natali]

New submission from Charles-Francois Natali <neologix at free.fr>:

Some posix module functions unnecessarily release the GIL.
For example, posix_dup, posix_dup2 and posix_pipe all release the GIL, but those are non-blocking syscalls (the don't imply any I/O, only modifying the process file descriptors table).
This leads to the famous convoy effect (see http://bugs.python.org/issue7946).

For example:

$ cat /tmp/test_dup2.py 
import os
import threading
import sys
import time


def do_loop():
    while True:
        pass

t = threading.Thread(target=do_loop)
t.setDaemon(True)
t.start()

f = os.open(sys.argv[1], os.O_RDONLY)

for i in range(4, 1000):
    os.dup2(f, i)

Whith  GIL release/acquire:

$ time ./python /tmp/test_dup2.py  /etc/fstab 

real    0m5.238s
user    0m5.223s
sys     0m0.009s

$ time ./python /tmp/test_pipe.py 

real    0m3.083s
user    0m3.074s
sys     0m0.007s

Without GIL release/acquire:

$ time ./python /tmp/test_dup2.py  /etc/fstab 

real    0m0.094s
user    0m0.077s
sys     0m0.010s

$ time ./python /tmp/test_pipe.py 

real    0m0.088s
user    0m0.074s
sys     0m0.008s

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title: some posix module functions -> some posix module functions unnecessarily release the GIL

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue11382>
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