[Python-Dev] PEP Draft: Simplified Global Interpreter Lock acquisition for extensions

[Guido van Rossum]

> > One question: you claim that some implementation of TLS (Thread Local
> > Storage) is required to implement this API, but you don't give enough
> > implementation details to explain this requirement.
> >
> > I wonder if instead of relying on TLS, you could return a void*
> > pointer from PyAutoThreadState_Ensure() which must be passed back into
> > PyAutoThreadState_Release()?  Or is TLS used for something else too?
> 
> OK, I will re-work that portion.  I just came up with the following
> justification:
> 
>     A platform TLS implementation is required to correctly support
>     PyThreadState semantics.  It is assumed that it is an error if
>     two discrete PyThreadStates are used for a single thread.
>     Comments in pystate.h ("State unique per thread") support this
>     view, although it is never directly stated.  Thus, this
>     implementation will require some abstraction to allow at least
>     per-thread storage of a simple pointer to a thread's existing
>     PyThreadState.

Thanks, that explains it.

> > (I'm not a big fan of TLS, mostly because its API is different for
> > each native thread package; requiring it would make the burden of
> > providing the PyAutoThreadState API bigger.)
> 
> In the thread that started this discussion, it was noted that nobody needs
> to support "screw-ball", or even old, platforms.  All complicated extensions
> that require PyAutoThreadState only run on "major" platforms.  Everybody
> seemed happy if only Windows, Mac and pthreads were supported.

OK.

> Anyway, I do not propose that a platform provide a *complete* TLS
> implementation - all I need is a way to get a per-thread pointer.  I expect
> that if we keep the bar that low, most platforms with a TLS API of any
> description should be able to provide this facility without too much pain.
> 
> I'll post a new PEP up with comments I have recieved, as well as a
> clarification on the TLS, shortly.

Great!

When can we expect code? :-)

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