X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fthread%2Fpthread_cond_timedwait.c;h=6b761455c47f0f8c8afde4e2d57768208efc06ba;hb=3f701faace7addc75d16dea8a6cd769fa5b3f260;hp=7aaba95475957719fa0119eb9247bc02ed32da66;hpb=37195db8ec31300a87bc7ec09d2adcf299e9203d;p=musl

diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index 7aaba954..6b761455 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -10,12 +10,10 @@
  * degenerate list of one member.
  *
  * Waiter lists attached to the condition variable itself are
- * protected by the lock on the cv. Detached waiter lists are
- * protected by the associated mutex. The hand-off between protections
- * is handled by a "barrier" lock in each node, which disallows
- * signaled waiters from making forward progress to the code that will
- * access the list using the mutex until the list is in a consistent
- * state and the cv lock as been released.
+ * protected by the lock on the cv. Detached waiter lists are never
+ * modified again, but can only be traversed in reverse order, and are
+ * protected by the "barrier" locks in each node, which are unlocked
+ * in turn to control wake order.
  *
  * Since process-shared cond var semantics do not necessarily allow
  * one thread to see another's automatic storage (they may be in
@@ -26,11 +24,8 @@
 
 struct waiter {
 	struct waiter *prev, *next;
-	int state, barrier, requeued, mutex_ret;
-	int *notify;
-	pthread_mutex_t *mutex;
-	pthread_cond_t *cond;
-	int shared;
+	volatile int state, barrier;
+	volatile int *notify;
 };
 
 /* Self-synchronized-destruction-safe lock functions */
@@ -50,96 +45,25 @@ 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|FUTEX_PRIVATE, 0, 1, r) != -ENOSYS
+		|| __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
+}
+
 enum {
 	WAITING,
 	SIGNALED,
 	LEAVING,
 };
 
-static void unwait(void *arg)
+int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
 {
-	struct waiter *node = arg, *p;
-
-	if (node->shared) {
-		pthread_cond_t *c = node->cond;
-		pthread_mutex_t *m = node->mutex;
-		if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
-			__wake(&c->_c_waiters, 1, 0);
-		node->mutex_ret = pthread_mutex_lock(m);
-		return;
-	}
-
-	int oldstate = a_cas(&node->state, WAITING, LEAVING);
-
-	if (oldstate == WAITING) {
-		/* Access to cv object is valid because this waiter was not
-		 * yet signaled and a new signal/broadcast cannot return
-		 * after seeing a LEAVING waiter without getting notified
-		 * via the futex notify below. */
-
-		pthread_cond_t *c = node->cond;
-		lock(&c->_c_lock);
-		
-		if (c->_c_head == node) c->_c_head = node->next;
-		else if (node->prev) node->prev->next = node->next;
-		if (c->_c_tail == node) c->_c_tail = node->prev;
-		else if (node->next) node->next->prev = node->prev;
-		
-		unlock(&c->_c_lock);
-
-		if (node->notify) {
-			if (a_fetch_add(node->notify, -1)==1)
-				__wake(node->notify, 1, 1);
-		}
-	}
-
-	node->mutex_ret = pthread_mutex_lock(node->mutex);
-
-	if (oldstate == WAITING) return;
-
-	/* If the mutex can't be locked, we're in big trouble because
-	 * it's all that protects access to the shared list state.
-	 * In order to prevent catastrophic stack corruption from
-	 * unsynchronized access, simply deadlock. */
-	if (node->mutex_ret && node->mutex_ret != EOWNERDEAD)
-		for (;;) lock(&(int){0});
-
-	/* Wait until control of the list has been handed over from
-	 * the cv lock (signaling thread) to the mutex (waiters). */
-	lock(&node->barrier);
-
-	/* 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);
-
-	/* Find a thread to requeue to the mutex, starting from the
-	 * end of the list (oldest waiters). */
-	for (p=node; p->next; p=p->next);
-	if (p==node) p=node->prev;
-	for (; p && p->requeued; p=p->prev);
-	if (p==node) p=node->prev;
-	if (p) {
-		p->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, &p->state, FUTEX_REQUEUE|128,
-			wake, 1, &node->mutex->_m_lock) != -EINVAL
-		|| __syscall(SYS_futex, &p->state, FUTEX_REQUEUE,
-			0, 1, &node->mutex->_m_lock);
-	}
-
-	/* Remove this thread from the list. */
-	if (node->next) node->next->prev = node->prev;
-	if (node->prev) node->prev->next = node->next;
-}
-
-int pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
-{
-	struct waiter node = { .cond = c, .mutex = m };
-	int e, seq, *fut, clock = c->_c_clock;
+	struct waiter node = { 0 };
+	int e, seq, clock = c->_c_clock, cs, shared=0, oldstate, tmp;
+	volatile int *fut;
 
 	if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
 		return EPERM;
@@ -147,19 +71,19 @@ int pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict
 	if (ts && ts->tv_nsec >= 1000000000UL)
 		return EINVAL;
 
-	pthread_testcancel();
+	__pthread_testcancel();
 
 	if (c->_c_shared) {
-		node.shared = 1;
+		shared = 1;
 		fut = &c->_c_seq;
 		seq = c->_c_seq;
 		a_inc(&c->_c_waiters);
 	} 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;
@@ -168,35 +92,101 @@ int pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict
 		unlock(&c->_c_lock);
 	}
 
-	pthread_mutex_unlock(m);
+	__pthread_mutex_unlock(m);
 
-	do e = __timedwait(fut, seq, clock, ts, unwait, &node, !node.shared);
+	__pthread_setcancelstate(PTHREAD_CANCEL_MASKED, &cs);
+	if (cs == PTHREAD_CANCEL_DISABLE) __pthread_setcancelstate(cs, 0);
+
+	do e = __timedwait_cp(fut, seq, clock, ts, !shared);
 	while (*fut==seq && (!e || e==EINTR));
 	if (e == EINTR) e = 0;
 
-	unwait(&node);
+	if (shared) {
+		/* Suppress cancellation if a signal was potentially
+		 * consumed; this is a legitimate form of spurious
+		 * wake even if not. */
+		if (e == ECANCELED && c->_c_seq != seq) e = 0;
+		if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
+			__wake(&c->_c_waiters, 1, 0);
+		oldstate = WAITING;
+		goto relock;
+	}
+
+	oldstate = a_cas(&node.state, WAITING, LEAVING);
+
+	if (oldstate == WAITING) {
+		/* Access to cv object is valid because this waiter was not
+		 * yet signaled and a new signal/broadcast cannot return
+		 * after seeing a LEAVING waiter without getting notified
+		 * via the futex notify below. */
 
-	return node.mutex_ret ? node.mutex_ret : e;
+		lock(&c->_c_lock);
+		
+		if (c->_c_head == &node) c->_c_head = node.next;
+		else if (node.prev) node.prev->next = node.next;
+		if (c->_c_tail == &node) c->_c_tail = node.prev;
+		else if (node.next) node.next->prev = node.prev;
+		
+		unlock(&c->_c_lock);
+
+		if (node.notify) {
+			if (a_fetch_add(node.notify, -1)==1)
+				__wake(node.notify, 1, 1);
+		}
+	} else {
+		/* Lock barrier first to control wake order. */
+		lock(&node.barrier);
+	}
+
+relock:
+	/* Errors locking the mutex override any existing error or
+	 * cancellation, since the caller must see them to know the
+	 * state of the mutex. */
+	if ((tmp = pthread_mutex_lock(m))) e = tmp;
+
+	if (oldstate == WAITING) goto done;
+
+	if (!node.next && !(m->_m_type & 8))
+		a_inc(&m->_m_waiters);
+
+	/* Unlock the barrier that's holding back the next waiter, and
+	 * either wake it or requeue it to the mutex. */
+	if (node.prev) {
+		int val = m->_m_lock;
+		if (val>0) a_cas(&m->_m_lock, val, val|0x80000000);
+		unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & (8|128));
+	} else if (!(m->_m_type & 8)) {
+		a_dec(&m->_m_waiters);		
+	}
+
+	/* Since a signal was consumed, cancellation is not permitted. */
+	if (e == ECANCELED) e = 0;
+
+done:
+	__pthread_setcancelstate(cs, 0);
+
+	if (e == ECANCELED) {
+		__pthread_testcancel();
+		__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
+	}
+
+	return e;
 }
 
 int __private_cond_signal(pthread_cond_t *c, int n)
 {
-	struct waiter *p, *q=0;
-	int ref = 0, cur;
+	struct waiter *p, *first=0;
+	volatile int ref = 0;
+	int cur;
 
 	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;
 		} else {
 			n--;
-			if (!q) q=p;
+			if (!first) first=p;
 		}
 	}
 	/* Split the list, leaving any remainder on the cv. */
@@ -214,12 +204,10 @@ int __private_cond_signal(pthread_cond_t *c, int n)
 	 * signaled threads to proceed. */
 	while ((cur = ref)) __wait(&ref, 0, cur, 1);
 
-	/* Wake the first signaled thread and unlock the per-waiter
-	 * barriers preventing their forward progress. */
-	for (p=q; p; p=q) {
-		q = p->prev;
-		if (!p->next) __wake(&p->state, 1, 1);
-		unlock(&p->barrier);
-	}
+	/* Allow first signaled waiter, if any, to proceed. */
+	if (first) unlock(&first->barrier);
+
 	return 0;
 }
+
+weak_alias(__pthread_cond_timedwait, pthread_cond_timedwait);