On Oct 7, 2011, at 8:45 PM, Graham Dumpleton wrote:
> Hmmm, the local setup I thought I was getting this issue on, I am not,
> The error on my local setup was:
>
> [Fri Sep 23 15:05:13 2011] [notice] child pid 97541 exit signal Abort trap (6)
> Fatal Python error: XXX block stack underflow
>
> So, something entirely different.
>
> If you can distill that test case down to exclude subprocess it would
> thus help because if it is anything would suspect subprocess doing
> something.
I can reliably reproduce the problem thusly:
pid = os.fork()
if pid:
sys.stderr.write('Fork succeeded (PID=%s)\n' % pid)
return ['OK - ', pid]
else:
sys.stderr.write('Fork succeeded (child PID=%s)\n' % os.getpid())
os._exit(0)
Here's a small excerpt from my error log, the result of reloading the page four
times:
[Fri Oct 07 08:15:15 2011] [error] Fork succeeded (PID=90595)
[Fri Oct 07 08:15:15 2011] [error] Fork succeeded (child PID=90595)
[Fri Oct 07 08:15:35 2011] [error] Fork succeeded (PID=90599)
Fatal Python error: Couldn't create autoTLSkey mapping
[Fri Oct 07 08:15:43 2011] [error] Fork succeeded (PID=90600)
[Fri Oct 07 08:15:43 2011] [error] Fork succeeded (child PID=90600)
[Fri Oct 07 08:15:45 2011] [error] Fork succeeded (PID=90601)
Fatal Python error: Couldn't create autoTLSkey mapping
> If you aren't already, try adding:
>
> WSGIApplicationGroup %{GLOBAL}
>
> into Apache configuration just for that WSGI application.
That made the problem go away.
> This issue if there is one is likely going to relate to subprocess and
> forking in sub interpreters.
I'm pretty sure the error is being generated by this code in pystate.py:
/* Reset the TLS key - called by PyOS_AfterFork.
* This should not be necessary, but some - buggy - pthread implementations
* don't flush TLS on fork, see issue #10517.
*/
void
_PyGILState_Reinit(void)
{
PyThreadState *tstate = PyGILState_GetThisThreadState();
PyThread_delete_key(autoTLSkey);
if ((autoTLSkey = PyThread_create_key()) == -1)
Py_FatalError("Could not allocate TLS entry");
/* re-associate the current thread state with the new key */
if (PyThread_set_key_value(autoTLSkey, (void *)tstate) < 0)
Py_FatalError("Couldn't create autoTLSkey mapping");
}
> If all the process is then doing is subsequent exec then it is
> generally not a problem. It is when it wants to do mored complicate
> stuff that it becomes an issue. So to blanket say it is a really bad
> idea is plain wrong.
Yes, but this is not a C program, this is a Python program. Unless the
subprocess module is re-coded in C, it is not possible to call exec immediately
after fork. After calling fork from Python, control is necessarily returned to
the Python interpreter.
rg
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