[Python-Dev] Proposal to drop f_tstate

[Guido van Rossum]

> For years, there has been a f_tstate field in frames.
> 
> During my implementation of thread pickling for Stackless,
> I investigated how much use is made of this field.
> I found out that it is only used in rare cases, only, and can
> be most probably replaced by PyThreadState_GET() in the
> six or seven cases where it is touched at all.
> 
> f_tstate would make sense if PyThreadState_GET() wasn't
> such a cheap macro. It also would make sense if it were used
> somewhere to assure proper allocation of a frame to its tstate.
> But this is nowhere used.
> In the case of Stackless, f_tstate turns out to be even a
> drawback, since non-recursively called frames can be freely
> moved between real threads, and I'm saving updates to f_tstate
> already, simply by removing it.
> 
> I also didn't find any external module that uses f_tstate.
> 
> Therefore, I hereby propose to remove this frame field,
> in order to save space.
> 
> I also offer to provide the simple patch, right now.

I notice that all the places that use f_tstate are functions that get
a frame passed in.  What makes you believe that those always run in
the same thread where the frame was created?

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