diff options
| -rw-r--r-- | src/thread/pthread_cond_timedwait.c | 50 |
1 files changed, 21 insertions, 29 deletions
diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c index 52e306b2..c5cf66c3 100644 --- a/src/thread/pthread_cond_timedwait.c +++ b/src/thread/pthread_cond_timedwait.c @@ -24,7 +24,7 @@ struct waiter { struct waiter *prev, *next; - int state, barrier, requeued, mutex_ret; + int state, barrier, mutex_ret; int *notify; pthread_mutex_t *mutex; pthread_cond_t *cond; @@ -48,6 +48,14 @@ static inline void unlock(volatile int *l) __wake(l, 1, 1); } +static inline void unlock_requeue(volatile int *l, volatile int *r, int w) +{ + a_store(l, 0); + if (w) __wake(l, 1, 1); + else __syscall(SYS_futex, l, FUTEX_REQUEUE|128, 0, 1, r) != -EINVAL + || __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r); +} + enum { WAITING, SIGNALED, @@ -98,24 +106,16 @@ static void unwait(void *arg) if (oldstate == WAITING) return; - /* If this thread was requeued to the mutex, undo the extra - * waiter count that was added to the mutex. */ - if (node->requeued) a_dec(&node->mutex->_m_waiters); + if (!node->next) a_inc(&node->mutex->_m_waiters); - /* Unlock the barrier that's holding back the next waiter, - * and either wake it or requeue it to the mutex. */ + /* Unlock the barrier that's holding back the next waiter, and + * either wake it or requeue it to the mutex. */ if (node->prev) { - unlock(&node->prev->barrier); - node->prev->requeued = 1; - a_inc(&node->mutex->_m_waiters); - /* The futex requeue command cannot requeue from - * private to shared, so for process-shared mutexes, - * simply wake the target. */ - int wake = node->mutex->_m_type & 128; - __syscall(SYS_futex, &node->prev->state, FUTEX_REQUEUE|128, - wake, 1, &node->mutex->_m_lock) != -EINVAL - || __syscall(SYS_futex, &node->prev->state, FUTEX_REQUEUE, - 0, 1, &node->mutex->_m_lock); + unlock_requeue(&node->prev->barrier, + &node->mutex->_m_lock, + node->mutex->_m_type & 128); + } else { + a_dec(&node->mutex->_m_waiters); } } @@ -140,9 +140,9 @@ int pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict } else { lock(&c->_c_lock); - node.barrier = 1; - fut = &node.state; - seq = node.state = WAITING; + seq = node.barrier = 2; + fut = &node.barrier; + node.state = WAITING; node.next = c->_c_head; c->_c_head = &node; if (!c->_c_tail) c->_c_tail = &node; @@ -169,11 +169,6 @@ int __private_cond_signal(pthread_cond_t *c, int n) lock(&c->_c_lock); for (p=c->_c_tail; n && p; p=p->prev) { - /* The per-waiter-node barrier lock is held at this - * point, so while the following CAS may allow forward - * progress in the target thread, it doesn't allow - * access to the waiter list yet. Ideally the target - * does not run until the futex wake anyway. */ if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) { ref++; p->notify = &ref; @@ -198,10 +193,7 @@ int __private_cond_signal(pthread_cond_t *c, int n) while ((cur = ref)) __wait(&ref, 0, cur, 1); /* Allow first signaled waiter, if any, to proceed. */ - if (first) { - __wake(&first->state, 1, 1); - unlock(&first->barrier); - } + if (first) unlock(&first->barrier); return 0; } |