[Python-Dev] Possible GIL/threading issue involving subprocess and PyMem_MALLOC...
Kristján Valur Jónsson
kristjan at ccpgames.com
Fri Dec 21 10:31:44 CET 2012
I ran into this the other day. I had put in hooks in the PyMem_MALLOC to track memory per tasklet, and it crashed
in those cases because it was being called without the GIL. My local patch was simply to _not_ release the GIL.
Clearly, calling PyMem_MALLOC without the GIL is an API violation.
> -----Original Message-----
> From: Python-Dev [mailto:python-dev-
> bounces+kristjan=ccpgames.com at python.org] On Behalf Of Trent Nelson
> Sent: 21. desember 2012 03:13
> To: Gregory P. Smith
> Cc: Python-Dev
> Subject: Re: [Python-Dev] Possible GIL/threading issue involving subprocess
> and PyMem_MALLOC...
> On Thu, Dec 20, 2012 at 05:47:40PM -0800, Gregory P. Smith wrote:
> > On Thu, Dec 20, 2012 at 10:43 AM, Trent Nelson <trent at snakebite.org>
> > wrote:
> > This seems odd to me so I wanted to see what others think. The unit
> > test Lib/unittest/test/test_runner.py:Test_TextRunner.test_warnings
> > will eventually hit subprocess.Popen._communicate.
> > The `mswindows` implementation of this method relies on threads to
> > buffer stdin/stdout. That'll eventually result in
> > PyOs_StdioReadline
> > being called without the GIL being held. PyOs_StdioReadline calls
> > PyMem_MALLOC, PyMem_FREE and possibly PyMem_REALLOC.
> > Those threads are implemented in Python so how would the GIL ever not
> > held?
> > -gps
> PyOS_Readline drops the GIL prior to calling PyOS_StdioReadline:
> #ifdef WITH_THREAD
> PyThread_acquire_lock(_PyOS_ReadlineLock, 1);
> /* This is needed to handle the unlikely case that the
> * interpreter is in interactive mode *and* stdin/out are not
> * a tty. This can happen, for example if python is run like
> * this: python -i < test1.py
> if (!isatty (fileno (sys_stdin)) || !isatty (fileno (sys_stdout)))
> rv = PyOS_StdioReadline (sys_stdin, sys_stdout, prompt); ----------------
> rv = (*PyOS_ReadlineFunctionPointer)(sys_stdin, sys_stdout,
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