diff options
| -rw-r--r-- | linuxthreads/ChangeLog | 10 | ||||
| -rw-r--r-- | linuxthreads/spinlock.c | 14 | ||||
| -rw-r--r-- | linuxthreads/spinlock.h | 14 |
3 files changed, 22 insertions, 16 deletions
diff --git a/linuxthreads/ChangeLog b/linuxthreads/ChangeLog index 05ffaab5da..6282a60b8e 100644 --- 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 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)) diff --git a/linuxthreads/spinlock.h b/linuxthreads/spinlock.h index 0dbaa54e2d..0ec40c57cb 100644 --- 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 |