import in execv after fork

[Rotem]

Hello,

We have been encountering several deadlocks in a threaded Python
application which calls subprocess.Popen (i.e. fork()) in some of its
threads.

This has occurred on Python 2.4.1 on a 2.4.27 Linux kernel.

Perliminary analysis of the hang shows that the child process blocks
upon entering the execvp function, in which the import_lock is acquired
due to the following line:

def _execvpe(file, args, env=None):
from errno import ENOENT, ENOTDIR
...

It is known that when forking from a pthreaded application, acquisition
attempts on locks which were already locked by other threads while
fork() was called will deadlock.

Due to these oddities I was wondering if it would be better to extract
the above import line from the execvpe call, to prevent lock
acquisition attempts in such cases.

I'd appreciate any opinions you might have on the subject.


Thanks in advance,

Rotem

 

[Rotem]

Another workaround could be re-assigning a new lock to import_lock
(such a thing is done with the global interpreter lock) at
PyOS_AfterFork or pthread_atfork.