about summary refs log tree commit diff
path: root/linuxthreads/spinlock.c
diff options
context:
space:
mode:
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)
downloadglibc-47e5d2a8b132c73bc0659baad25714326fb333c9.tar.gz
glibc-47e5d2a8b132c73bc0659baad25714326fb333c9.tar.xz
glibc-47e5d2a8b132c73bc0659baad25714326fb333c9.zip
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 927cb19443..199386a4fc 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))