From: Rich Felker <dalias@aerifal.cx>
Date: Fri, 26 Apr 2013 20:05:39 +0000 (-0400)
Subject: use atomic decrement rather than cas in pthread_exit thread count
X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=commitdiff_plain;h=c3a6839ce95c0f93bd73f7fbe5fcaee4054e5b62

use atomic decrement rather than cas in pthread_exit thread count

now that blocking signals prevents any application code from running
while the last thread is exiting, the cas logic is no longer needed to
prevent decrementing below zero.
---

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 6a37ee9b..0567f966 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -12,7 +12,6 @@ weak_alias(dummy_0, __pthread_tsd_run_dtors);
 _Noreturn void pthread_exit(void *result)
 {
 	pthread_t self = pthread_self();
-	int n;
 
 	self->result = result;
 
@@ -38,9 +37,7 @@ _Noreturn void pthread_exit(void *result)
 	 * reasons as well. */
 	__syscall(SYS_rt_sigprocmask, SIG_BLOCK, SIGALL_SET, 0, _NSIG/8);
 
-	do n = libc.threads_minus_1;
-	while (n && a_cas(&libc.threads_minus_1, n, n-1)!=n);
-	if (!n) exit(0);
+	if (a_fetch_add(&libc.threads_minus_1, -1)==0) exit(0);
 
 	if (self->detached && self->map_base) {
 		/* Detached threads must avoid the kernel clear_child_tid