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Date: Wed, 15 Apr 2015 01:44:53 +0300
From: Alexander Monakov <>
Cc: Alexander Monakov <>
Subject: [PATCH] Use CAS instead of atomic swap to implement spinlock

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;

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