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authorUlrich Drepper <drepper@redhat.com>2001-05-24 23:38:52 +0000
committerUlrich Drepper <drepper@redhat.com>2001-05-24 23:38:52 +0000
commit47e5d2a8b132c73bc0659baad25714326fb333c9 (patch)
tree36c83a82b882e1d624374ac0956b8a870881ee52 /linuxthreads/spinlock.c
parent65fa1dec4ec6d800ba9e91abe0e4ae8208b9905e (diff)
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Update.
2001-05-24 Ulrich Drepper <drepper@redhat.com> * spinlock.c (__pthread_lock) [HAS_COMPARE_AND_SWAP]: Before doing any serious work try once whether the lock is uncontested. Remove duplicate reading of __status before loop. Change suggested by Hans Boehm <hans_boehm@hp.com>. * spinlock.h (__pthread_trylock): Remove need for oldstatus variable. (__pthread_alt_trylock): Likewise.
Diffstat (limited to 'linuxthreads/spinlock.c')
-rw-r--r--linuxthreads/spinlock.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/linuxthreads/spinlock.c b/linuxthreads/spinlock.c
index 927cb19..199386a 100644
--- a/linuxthreads/spinlock.c
+++ b/linuxthreads/spinlock.c
@@ -64,8 +64,8 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock,
{
#if defined HAS_COMPARE_AND_SWAP
long oldstatus, newstatus;
- int successful_seizure, spurious_wakeup_count = 0;
- int spin_count = 0;
+ int successful_seizure, spurious_wakeup_count;
+ int spin_count;
#endif
#if defined TEST_FOR_COMPARE_AND_SWAP
@@ -79,6 +79,14 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock,
#endif
#if defined HAS_COMPARE_AND_SWAP
+ /* First try it without preparation. Maybe it's a completely
+ uncontested lock. */
+ if (lock->__status == 0 && __compare_and_swap (&lock->__status, 0, 1))
+ return;
+
+ spurious_wakeup_count = 0;
+ spin_count = 0;
+
again:
/* On SMP, try spinning to get the lock. */
@@ -174,8 +182,6 @@ int __pthread_unlock(struct _pthread_fastlock * lock)
WRITE_MEMORY_BARRIER();
again:
- oldstatus = lock->__status;
-
while ((oldstatus = lock->__status) == 1) {
if (__compare_and_swap_with_release_semantics(&lock->__status,
oldstatus, 0))