Guido van Rossum wrote:
Yeah, I think imports inside functions are overused.
Rotem took the time to explain the problem to me more fully in private email, and it appears that using import statements inside functions is currently fundamentally unsafe in a posix environment where both multiple threads and fork() are used. If any thread other than the one invoking fork() holds the import lock at the time of the fork then import statements in the spawned process will deadlock. So I believe fixing this properly would indeed require assigning a new lock object in one of the two places Rotem suggested. Cheers, Nick.
On 5/9/06, Rotem Yaari <vmalloc@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 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 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 import_lock (such a thing is done with the global interpreter lock) at PyOS_AfterFork or pthread_atfork.
We'd appreciate any opinions you might have on the subject.
Thanks in advance,
Yair and Rotem _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/guido%40python.org
-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia --------------------------------------------------------------- http://www.boredomandlaziness.org