Bugs item #1590864, was opened at 2006-11-05 17:06
Message generated for change (Comment added) made by astrand
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Category: Python Library
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Michael Tsai (michaeltsai)
>Assigned to: Nobody/Anonymous (nobody)
>Summary: import deadlocks when using PyObjC threads
Initial Comment:
When I use subprocess.py from a child thread, sometimes it deadlocks. I
determined that the new process is blocked during an import:
#0 0x90024427 in semaphore_wait_signal_trap ()
#1 0x90028414 in pthread_cond_wait ()
#2 0x004c77bf in PyThread_acquire_lock (lock=0x3189a0, waitflag=1)
at Python/thread_pthread.h:452
#3 0x004ae2a6 in lock_import () at Python/import.c:266
#4 0x004b24be in PyImport_ImportModuleLevel (name=0xaad74 "errno",
globals=0xbaed0, locals=0x502aa0, fromlist=0xc1378, level=-1) at
Python/import.c:2054
#5 0x0048d2e2 in builtin___import__ (self=0x0, args=0x53724c90,
kwds=0x0) at Python/bltinmodule.c:47
#6 0x0040decb in PyObject_Call (func=0xa94b8, arg=0x53724c90,
kw=0x0) at Objects/abstract.c:1860
and that the code in question is in os.py:
def _execvpe(file, args, env=None):
from errno import ENOENT, ENOTDIR
I think the problem is that since exec (the C function) hasn't yet been
called in the new process, it's inherited from the fork a lock that's already
held. The main process will eventually release its copy of the lock, but this
will not unlock it in the new process, so it deadlocks.
If I change os.py so that it imports the constants outside of
_execvpe, the new process no longer blocks in this way.
This is on Mac OS X 10.4.8.
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>Comment By: Peter Åstrand (astrand)
Date: 2007-01-13 23:42
Message:
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Since both the reporter and I believes that this is not a bug in the
subprocess module, I'm stepping back.
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Comment By: Michael Tsai (michaeltsai)
Date: 2007-01-07 18:09
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I don't have time at the moment to write sample code that reproduces this.
But, FYI, I was using PyObjC to create the threads. It might not happen
with "threading" threads. And second, I think it's a bug in os.py, not in
subprocess.py. Sorry for the confusion.
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Comment By: Peter Åstrand (astrand)
Date: 2007-01-07 15:10
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Can you provide a test case or sample code that demonstrates this problem?
I'm a bit unsure of if this really is a subprocess bug or a more general
Python bug.
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