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Date: Thu, 18 May 2023 16:01:18 +0200
From: Jₑₙₛ Gustedt <jens.gustedt@...ia.fr>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com, 847567161 <847567161@...com>
Subject: Re: Question：Why musl call a_barrier in
__pthread_once?
Rich,
on Thu, 18 May 2023 09:29:05 -0400 you (Rich Felker <dalias@...c.org>)
wrote:
> Of course call_once is exempt from any such requirements
it was, but isn't anymore. In C23, now we have
Completion of an effective call to the `call_once` function
synchronizes with all subsequent calls to the `call_once` function
with the same value of `flag`.
POSIX (for which the ISO 9945 instantiation is currently at NB ballot)
also has updated all of this
The pthread_once() and call_once() functions shall synchronize
memory for the first successful call in each thread for a given
pthread_once_t or once_flag object, respectively. If the
init_routine called by pthread_once() or call_once() is a
cancellation point and is canceled, a successful call to
pthread_once() for the same pthread_once_t object or to
call_once() for the same once_flag object, made from a
cancellation cleanup handler shall also synchronize memory.
If I understand this correctly, the C11 interfaces become mandatory if
the platform supports threads.
Thanks
Jₑₙₛ
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