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Explicitly load atomic values in lib/isc/rwlock.c

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This commit is contained in:
Ondřej Surý
2018-08-17 19:21:12 +02:00
parent d1d15c03e2
commit b5709e5531
1 changed files with 34 additions and 21 deletions
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55
lib/isc/rwlock.c
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@@ -63,8 +63,10 @@ print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
ISC_MSG_READ, "read") : ISC_MSG_READ, "read") :
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK, isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_WRITE, "write")), ISC_MSG_WRITE, "write")),
rwl->write_requests, rwl->write_completions, atomic_load_explicit(&rwl->write_requests, memory_order_relaxed),
rwl->cnt_and_flag, rwl->readers_waiting, atomic_load_explicit(&rwl->write_completions, memory_order_relaxed),
atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed),
rwl->readers_waiting,
rwl->write_granted, rwl->write_quota); rwl->write_granted, rwl->write_quota);
} }
#endif /* ISC_RWLOCK_TRACE */ #endif /* ISC_RWLOCK_TRACE */
@@ -84,9 +86,9 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
rwl->magic = 0; rwl->magic = 0;
rwl->spins = 0; rwl->spins = 0;
rwl->write_requests = 0; atomic_init(&rwl->write_requests, 0);
rwl->write_completions = 0; atomic_init(&rwl->write_completions, 0);
rwl->cnt_and_flag = 0; atomic_init(&rwl->cnt_and_flag, 0);
rwl->readers_waiting = 0; rwl->readers_waiting = 0;
rwl->write_granted = 0; rwl->write_granted = 0;
if (read_quota != 0) { if (read_quota != 0) {
@@ -138,8 +140,9 @@ void
isc_rwlock_destroy(isc_rwlock_t *rwl) { isc_rwlock_destroy(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl)); REQUIRE(VALID_RWLOCK(rwl));
REQUIRE(rwl->write_requests == rwl->write_completions && REQUIRE(atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) ==
rwl->cnt_and_flag == 0 && rwl->readers_waiting == 0); atomic_load_explicit(&rwl->write_completions, memory_order_relaxed) &&
atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) == 0 && rwl->readers_waiting == 0);
rwl->magic = 0; rwl->magic = 0;
(void)isc_condition_destroy(&rwl->readable); (void)isc_condition_destroy(&rwl->readable);
@@ -224,10 +227,13 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
#endif #endif
if (type == isc_rwlocktype_read) { if (type == isc_rwlocktype_read) {
if (rwl->write_requests != rwl->write_completions) { if (atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_completions, memory_order_relaxed))
{
/* there is a waiting or active writer */ /* there is a waiting or active writer */
LOCK(&rwl->lock); LOCK(&rwl->lock);
if (rwl->write_requests != rwl->write_completions) { if (atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_completions, memory_order_relaxed)) {
rwl->readers_waiting++; rwl->readers_waiting++;
WAIT(&rwl->readable, &rwl->lock); WAIT(&rwl->readable, &rwl->lock);
rwl->readers_waiting--; rwl->readers_waiting--;
@@ -240,14 +246,15 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
memory_order_relaxed); memory_order_relaxed);
POST(cntflag); POST(cntflag);
while (1) { while (1) {
if ((rwl->cnt_and_flag & WRITER_ACTIVE) == 0) if ((atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) & WRITER_ACTIVE) == 0)
break; break;
/* A writer is still working */ /* A writer is still working */
LOCK(&rwl->lock); LOCK(&rwl->lock);
rwl->readers_waiting++; rwl->readers_waiting++;
if ((rwl->cnt_and_flag & WRITER_ACTIVE) != 0) if ((atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) & WRITER_ACTIVE) != 0) {
WAIT(&rwl->readable, &rwl->lock); WAIT(&rwl->readable, &rwl->lock);
}
rwl->readers_waiting--; rwl->readers_waiting--;
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
@@ -289,9 +296,9 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
/* enter the waiting queue, and wait for our turn */ /* enter the waiting queue, and wait for our turn */
prev_writer = atomic_fetch_add_explicit(&rwl->write_requests, 1, prev_writer = atomic_fetch_add_explicit(&rwl->write_requests, 1,
memory_order_relaxed); memory_order_relaxed);
while (rwl->write_completions != prev_writer) { while (atomic_load_explicit(&rwl->write_completions, memory_order_relaxed) != prev_writer) {
LOCK(&rwl->lock); LOCK(&rwl->lock);
if (rwl->write_completions != prev_writer) { if (atomic_load_explicit(&rwl->write_completions, memory_order_relaxed) != prev_writer) {
WAIT(&rwl->writeable, &rwl->lock); WAIT(&rwl->writeable, &rwl->lock);
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
continue; continue;
@@ -311,12 +318,13 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
/* Another active reader or writer is working. */ /* Another active reader or writer is working. */
LOCK(&rwl->lock); LOCK(&rwl->lock);
if (rwl->cnt_and_flag != 0) if (atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) != 0) {
WAIT(&rwl->writeable, &rwl->lock); WAIT(&rwl->writeable, &rwl->lock);
}
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
} }
INSIST((rwl->cnt_and_flag & WRITER_ACTIVE) != 0); INSIST((atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) & WRITER_ACTIVE));
rwl->write_granted++; rwl->write_granted++;
} }
@@ -365,7 +373,8 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
if (type == isc_rwlocktype_read) { if (type == isc_rwlocktype_read) {
/* If a writer is waiting or working, we fail. */ /* If a writer is waiting or working, we fail. */
if (rwl->write_requests != rwl->write_completions) if (atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_completions, memory_order_relaxed))
return (ISC_R_LOCKBUSY); return (ISC_R_LOCKBUSY);
/* Otherwise, be ready for reading. */ /* Otherwise, be ready for reading. */
@@ -385,7 +394,8 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
* new writers in this short period, wake them up. * new writers in this short period, wake them up.
*/ */
if (cntflag == READER_INCR && if (cntflag == READER_INCR &&
rwl->write_completions != rwl->write_requests) { atomic_load_explicit(&rwl->write_completions, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_requests, memory_order_relaxed)) {
LOCK(&rwl->lock); LOCK(&rwl->lock);
BROADCAST(&rwl->writeable); BROADCAST(&rwl->writeable);
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
@@ -501,7 +511,8 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
* FIFO order. * FIFO order.
*/ */
if (prev_cnt == READER_INCR && if (prev_cnt == READER_INCR &&
rwl->write_completions != rwl->write_requests) { atomic_load_explicit(&rwl->write_completions, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_requests, memory_order_relaxed)) {
LOCK(&rwl->lock); LOCK(&rwl->lock);
BROADCAST(&rwl->writeable); BROADCAST(&rwl->writeable);
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
@@ -519,8 +530,9 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
memory_order_relaxed); memory_order_relaxed);
if (rwl->write_granted >= rwl->write_quota || if (rwl->write_granted >= rwl->write_quota ||
rwl->write_requests == rwl->write_completions || (atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) ==
(rwl->cnt_and_flag & ~WRITER_ACTIVE) != 0) { atomic_load_explicit(&rwl->write_completions, memory_order_relaxed)) ||
(atomic_load_explicit(&rwl->cnt_and_flag, memory_order_relaxed) & ~WRITER_ACTIVE)) {
/* /*
* We have passed the write quota, no writer is * We have passed the write quota, no writer is
* waiting, or some readers are almost ready, pending * waiting, or some readers are almost ready, pending
@@ -537,7 +549,8 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
UNLOCK(&rwl->lock); UNLOCK(&rwl->lock);
} }
if (rwl->write_requests != rwl->write_completions && if ((atomic_load_explicit(&rwl->write_requests, memory_order_relaxed) !=
atomic_load_explicit(&rwl->write_completions, memory_order_relaxed)) &&
wakeup_writers) { wakeup_writers) {
LOCK(&rwl->lock); LOCK(&rwl->lock);
BROADCAST(&rwl->writeable); BROADCAST(&rwl->writeable);