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Date: Sat, 18 Apr 2015 20:24:33 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] Use CAS instead of atomic swap to implement
spinlock
On Wed, Apr 15, 2015 at 01:44:53AM +0300, Alexander Monakov wrote:
> This should allow spinning without constantly dirtying cache lines holding the
> spinlock value. On architectures without native atomic swap, musl implement
> a_swap by looping around a_cas.
> ---
> If I'm not mistaken this was also suggested by nsz on IRC.
>
> src/thread/pthread_spin_lock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/thread/pthread_spin_lock.c b/src/thread/pthread_spin_lock.c
> index df575f0..dabcb31 100644
> --- a/src/thread/pthread_spin_lock.c
> +++ b/src/thread/pthread_spin_lock.c
> @@ -2,6 +2,6 @@
>
> int pthread_spin_lock(pthread_spinlock_t *s)
> {
> - while (a_swap(s, 1)) a_spin();
> + while (a_cas(s, 0, 1)) a_spin();
> return 0;
> }
Would it perhaps be better to do something like this?
while (*(volatile int *)s || a_cas(s, 0, 1)) a_spin();
Rich
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