[Python-Dev] pthreads, fork, import, and execvp (original) (raw)

Guido van Rossum guido at python.org
Fri May 12 06:48:35 CEST 2006

Yeah, I think imports inside functions are overused.

On 5/9/06, Rotem Yaari <vmalloc at gmail.com> wrote:

Hello everyone!

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. Preliminary analysis of the hang shows that the child process blocks upon entering the execvp function, in which the importlock 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 we were wondering if it would be better to extract the above import line from the execvpe call, to prevent lock acquisition attempts in such cases. Another workaround could be re-assigning a new lock to importlock (such a thing is done with the global interpreter lock) at PyOSAfterFork or pthreadatfork. We'd appreciate any opinions you might have on the subject. Thanks in advance, Yair and Rotem

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-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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