On Wed, Sep 9, 2009 at 23:56, Nick Coghlan <ncoghlan@gmail.com> wrote:
Thomas Wouters wrote:
>     Your idea of making this an API called a 'fork lock' or something
>     sounds good (though I think it needs a better name.  PyBeforeFork &
>     PyAfterFork?).  The subprocess module, for example, disables garbage
>     collection before forking and restores it afterwards to avoid
>     http://bugs.python.org/issue1336.  That type of thing could also be
>     done in such a function.
> Unfortunately it's rather hard to make those functions work correctly
> with the current API -- we can't provide functions you can just use as
> arguments to pthread_atfork because the global interpreter lock is not
> re-entrant and we have no way of testing whether the current thread
> holds the GIL.

I thought "make sure I have the GIL, either by already having it or
waiting for it if I don't yet have it" was the entire point of the
PyGILState_Ensure() API? [1]

Hm, yeah. For some reason I was certain it was inappropriate, back when I was trying to create a pthread_atfork-friendly set of functions. At the time I was also hip-deep in the awfulness of Python/thread*.c and its unsafe punning and unwarranted assumptions, so I may have overreacted. I added this as a feature-request issue ( http://bugs.python.org/issue6923 ) and will look at it some more.

In the mean time, I fixed the biggest source of issues by checking in the change to make at least calls to fork() made by Python be safe, also backported to 2.6.

Thomas Wouters <thomas@python.org>

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