[Python-Dev] Reworking the GIL

[Antoine Pitrou]

Terry Reedy <tjreedy <at> udel.edu> writes:
> 
> I am curious as to whether the entire mechanism is or can be turned off 
> when not needed -- when there are not threads (other than the main, 
> starting thread)?

It is an implicit feature: when no thread is waiting on the GIL, the GIL-holding
thread isn't notified and doesn't try to release it at all (in the eval loop,
that is; GIL-releasing C extensions still release it).

Note that "no thread is waiting on the GIL" can mean one of two things:
- either there is only one Python thread
- or the other Python threads are doing things with the GIL released (zlib/bz2
compression, waiting on I/O, sleep()ing, etc.)

So, yes, it automatically "turns itself off".

Regards

Antoine.