[Python-Dev] Encoding of PyFrameObject members

[Gregory P. Smith]

On Sun Feb 08 2015 at 12:21:36 AM Victor Stinner <victor.stinner at gmail.com>
wrote:

>
> Le 8 févr. 2015 05:39, "Gregory P. Smith" <greg at krypto.org> a écrit :
> > From there, in your signal handler you must try to acquire the newly
> exposed keymutex and (...)
>
> Stop! Acquiring a lock in a signal handler is just a crazy idea. It's very
> far from an async signal-safe function.
>
I'd normally agree... In this case, sem_trywait() is non-blocking. It is
unfortunately not on the official POSIX list of async-signal-safe functions
(of the SEMs, only sem_post() is) but many implementations actually are
safe, documented or not.

https://github.com/lattera/glibc/blob/master/nptl/sysdeps/unix/sysv/linux/x86_64/sem_trywait.S
- appears safe.

So long as the underlying semaphore is implemented using an atomic
instruction on the target platform I wouldn't expect any implementation of
sem_trywait to be async signal unsafe. (nor would I depend on that without
checking)

-gps

> > So until those are fixed (hooray for Antoine's PEP!), ...
>
> I wrote the PEP with Charles François Natali, but Charles wrote the whole
> implementation. Antoine also helped us and approved the PEP. It's the
> french connection! Just to say that Charles did most of the work.
>
> Victor
>
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