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Make isc_rwlock_t.spins thread-safe

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Ondřej Surý
2019-05-14 00:35:43 +07:00
parent ca6fc94400
commit 83f06fd8e1
2 changed files with 5 additions and 7 deletions
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lib/isc/include/isc/rwlock.h
+1 -1
View File
@@ -35,7 +35,7 @@ struct isc_rwlock {
/* Unlocked. */
unsigned int magic;
isc_mutex_t lock;
int32_t spins;
atomic_int_fast32_t spins;
/*
* When some atomic instructions with hardware assistance are
lib/isc/rwlock.c
+4 -6
View File
@@ -101,7 +101,7 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
*/
rwl->magic = 0;
rwl->spins = 0;
atomic_init(&rwl->spins, 0);
atomic_init(&rwl->write_requests, 0);
atomic_init(&rwl->write_completions, 0);
atomic_init(&rwl->cnt_and_flag, 0);
@@ -326,12 +326,10 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
isc_result_t
isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
int32_t cnt = 0;
int32_t max_cnt = rwl->spins * 2 + 10;
int32_t spins = atomic_load_acquire(&rwl->spins) * 2 + 10;
int32_t max_cnt = ISC_MAX(spins, RWLOCK_MAX_ADAPTIVE_COUNT);
isc_result_t result = ISC_R_SUCCESS;
if (max_cnt > RWLOCK_MAX_ADAPTIVE_COUNT)
max_cnt = RWLOCK_MAX_ADAPTIVE_COUNT;
do {
if (cnt++ >= max_cnt) {
result = isc__rwlock_lock(rwl, type);
@@ -340,7 +338,7 @@ isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
isc_rwlock_pause();
} while (isc_rwlock_trylock(rwl, type) != ISC_R_SUCCESS);
rwl->spins += (cnt - rwl->spins) / 8;
atomic_fetch_add_relaxed(&rwl->spins, (cnt - spins) / 8);
return (result);
}