sbt <[email protected]> added the comment:
Attached is a patch (without documentation) which creates an atfork module for
Unix.
Apart from the atfork() function modelled on pthread_atfork() there is also a
get_fork_lock() function. This returns a recursive lock which is held whenever
a child process is created using os.fork(), subprocess.Popen() or
multiprocessing.Process(). It can be used like
with atfork.get_fork_lock():
r, w = os.pipe()
pid = os.fork()
if pid == 0:
try:
os.close(r)
# do something with w
finally:
os._exit(0)
else:
os.close(w)
# do something with r
This prevents processes forked by other threads from accidentally inheriting
the writable end (which would potentially cause EOF to be delayed when reading
from the pipe). It can also be used to eliminate the potential race where you
create an fd and then set the CLOEXEC flag on it.
The patch modifies Popen() and Process.start() to acquire the lock when they
create their pipes. (A race condition previously made Process.sentinel and
Process.join() potentially unreliable in a multithreaded program.)
Note that using the deprecated os.popen?() and os.spawn?() functions can still
cause accidental inheritance of fds.
(I have also done a hopefully complete patch to multiprocessing to optionally
allow fork+exec on Unix -- see Issue 8713.)
----------
Added file: http://bugs.python.org/file24303/atfork.patch
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<http://bugs.python.org/issue6721>
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