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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.
This commit is contained in:
Ulrich Drepper 2001-05-24 23:38:52 +00:00
parent 65fa1dec4e
commit 47e5d2a8b1
3 changed files with 22 additions and 16 deletions
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10
linuxthreads/ChangeLog
View file

@ -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.

14
linuxthreads/spinlock.c
View file

@ -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))

14
linuxthreads/spinlock.h
View file

@ -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