[Python-Dev] PEP Draft: Simplified Global Interpreter Lock acquisition for extensions (original) (raw)

Guido van Rossum guido@python.org
Thu, 06 Feb 2003 08:50:38 -0500

> 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 PyAutoThreadStateEnsure() which must be passed back into > PyAutoThreadStateRelease()? 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/)