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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 11:15:15 +0200
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From: Bruno Haible via Cygwin <cygwin@cygwin.com>
Reply-To: Bruno Haible <bruno@clisp.org>
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Noel Grandin wrote:
> > 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.
> > 
> 
> No, they only spin briefly, before calling into the OS to sleep - see the article about their internals here:
> 
> https://learn.microsoft.com/en-us/archive/msdn-magazine/2012/november/windows-with-c-the-evolution-of-synchronization-in-windows-and-c#slim-readerwriter-lock

Still: Does ReleaseSRWLockExclusive notify other threads?

> Alternatively, Windows already has an API for init-once i.e.
>    https://learn.microsoft.com/en-us/windows/win32/sync/one-time-initialization

Functionally, the INIT_ONCE looks interesting. But, like Takashi Yano mentioned,
how would you make it fit into a pthread_once_t that is defined as
  struct { pthread_mutex_t mutex; int state; }
?

Bruno


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