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.

diff --git a/linuxthreads/ChangeLog b/linuxthreads/ChangeLog
index 05ffaab..6282a60 100644 (file)
--- a/linuxthreads/ChangeLog
+++ b/linuxthreads/ChangeLog
@@ -1,3 +1,13 @@
+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.
+
 2001-05-01  Kaz Kylheku  <kaz@ashi.footprints.net>
 
        Memory barrier overhaul following line by line inspection.

diff --git a/linuxthreads/spinlock.c b/linuxthreads/spinlock.c
index 927cb19..199386a 100644 (file)
--- 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))

diff --git a/linuxthreads/spinlock.h b/linuxthreads/spinlock.h
index 0dbaa54..0ec40c5 100644 (file)
--- a/linuxthreads/spinlock.h
+++ b/linuxthreads/spinlock.h
@@ -104,10 +104,6 @@ static inline void __pthread_init_lock(struct _pthread_fastlock * lock)
 
 static inline int __pthread_trylock (struct _pthread_fastlock * lock)
 {
-#if defined HAS_COMPARE_AND_SWAP
-  long oldstatus;
-#endif
-
 #if defined TEST_FOR_COMPARE_AND_SWAP
   if (!__pthread_has_cas)
 #endif
@@ -119,8 +115,7 @@ static inline int __pthread_trylock (struct _pthread_fastlock * lock)
 
 #if defined HAS_COMPARE_AND_SWAP
   do {
-    oldstatus = lock->__status;
-    if (oldstatus != 0) return EBUSY;
+    if (lock->__status != 0) return EBUSY;
   } while(! __compare_and_swap(&lock->__status, 0, 1));
   return 0;
 #endif
@@ -146,10 +141,6 @@ static inline void __pthread_alt_init_lock(struct _pthread_fastlock * lock)
 
 static inline int __pthread_alt_trylock (struct _pthread_fastlock * lock)
 {
-#if defined HAS_COMPARE_AND_SWAP
-  long oldstatus;
-#endif
-
 #if defined TEST_FOR_COMPARE_AND_SWAP
   if (!__pthread_has_cas)
 #endif
@@ -173,8 +164,7 @@ static inline int __pthread_alt_trylock (struct _pthread_fastlock * lock)
 
 #if defined HAS_COMPARE_AND_SWAP
   do {
-    oldstatus = lock->__status;
-    if (oldstatus != 0) return EBUSY;
+    if (lock->__status != 0) return EBUSY;
   } while(! compare_and_swap(&lock->__status, 0, 1, &lock->__spinlock));
   return 0;
 #endif