[Python-ideas] PEP 3156 / Tulip: Synchronization primitives

[Antoine Pitrou]

Le Thu, 7 Feb 2013 16:18:14 -0800,
Nikolay Kim <fafhrd91 at gmail.com> a écrit :
> I think Tulip should have synchronization primitives by default. 
> Here is my motivation:
> 
>   1. it is more convenient to use locking primitive with existing
> semantics rather than tulip magic. crawl.py example could use
> semaphore instead of tasks.wait with timeout 0. 2. while it seems
> easy to implement semaphore with tulip, it still requires deep
> understanding of tulips control flow. i had 2 not very obvious bugs
> in my semaphore implementation:
> 
>      a) release() could be called from different co-routines during
> same scheduling step. b) bug with acquire and release during same
> scheduling step. example:
>       1. task tries to acquire locked semaphore
>       2. other task releases semaphore
> 
>       in result - semaphore gets acquired 2 times at the end of
> scheduling step, because actual semaphore acquisition happens in
> "call_soon" and at this stage release() call is already released
> semaphore but first waiter does not acquire it yet.

I think Twisted has DeferredSemaphore for the same reasons.

Regards

Antoine.