From: Bruno Haible <bruno@clisp.org>
To: Takashi Yano <takashi.yano@nifty.ne.jp>,
cygwin@cygwin.com, Noel Grandin <noelgrandin@gmail.com>
Subject: Re: [PATCH v2] Cygwin: pthread: Fix a race issue introduced by the commit 2c5433e5da82
Date: Thu, 30 May 2024 10:47:38 +0200 [thread overview]
Message-ID: <1721092.SVj2RUA3Z2@nimes> (raw)
In-Reply-To: <0126a98a-3bdc-4303-a0d2-09f4c7009392@gmail.com>
Noel Grandin wrote in cygwin-patches:
> Pardon my ignorance, but why not rather use the Windows SRWLock functionality?
> https://learn.microsoft.com/en-us/windows/win32/sync/slim-reader-writer--srw--locks
>
> SRW locks are very fast, only require a single pointer-sized storage area, can be statically initialised, and do not
> need to be destroyed, so there is no possibibilty of memory leakage.
>
> Then the implementation simply becomes
>
> int pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
> {
> AcquireSRWLockExclusive(once_control->lock);
> if (!once_control->state)
> {
> init_routine()
> once_control->state = 1;
> }
> ReleaseSRWLockExclusive(once_control->lock);
> }
SRW locks are spin-locks. Since they are only pointer-sized,
ReleaseSRWLockExclusive cannot notify other threads — unlike CRITICAL_SECTION.
Therefore, AcquireSRWLockExclusive must busy-loop when the lock is already
held.
But busy-looping is a bad practice for pthread_once. In the case,
for example, that the init_routine reads a multi-megabyte data
structure into memory and parses it, the other threads that wait
on the result of this operation would by busy-looping, eating
full CPU time.
Bruno
next parent reply other threads:[~2024-05-30 8:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240530050538.53724-1-takashi.yano@nifty.ne.jp>
[not found] ` <0126a98a-3bdc-4303-a0d2-09f4c7009392@gmail.com>
2024-05-30 8:47 ` Bruno Haible [this message]
2024-05-30 8:59 ` Noel Grandin
2024-05-30 9:15 ` Bruno Haible
2024-05-30 10:28 ` Noel Grandin
2024-05-30 13:53 ` SRW locks Bruno Haible
2024-05-30 10:14 ` [PATCH v2] Cygwin: pthread: Fix a race issue introduced by the commit 2c5433e5da82 Bruno Haible
[not found] ` <20240530205012.2aff4d507acac144e50df2a4@nifty.ne.jp>
[not found] ` <20240530205918.7c730117b567bb3bec3a0c3f@nifty.ne.jp>
2024-05-30 13:38 ` Bruno Haible
2024-05-31 14:01 ` Bruno Haible
2024-06-01 14:18 ` Takashi Yano
2024-06-01 16:08 ` Ken Brown
2024-06-01 21:11 ` Takashi Yano
2024-06-02 13:14 ` Bruno Haible
2024-06-02 14:27 ` Takashi Yano
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