X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fthread%2Fpthread_cond_timedwait.c;h=6b761455c47f0f8c8afde4e2d57768208efc06ba;hb=1e4204d522670a1d8b8ab85f1cfefa960547e8af;hp=e9b5e2fcb82ffa4f76dd1efee77e5b2ca9d287db;hpb=729d6368bdf9faa33299cdfa68efc7422af33bd7;p=musl

diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index e9b5e2fc..6b761455 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -1,69 +1,213 @@
 #include "pthread_impl.h"
 
-struct cm {
-	pthread_cond_t *c;
-	pthread_mutex_t *m;
+/*
+ * struct waiter
+ *
+ * Waiter objects have automatic storage on the waiting thread, and
+ * are used in building a linked list representing waiters currently
+ * waiting on the condition variable or a group of waiters woken
+ * together by a broadcast or signal; in the case of signal, this is a
+ * 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 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
+ * different processes), the waiter list is not used for the
+ * process-shared case, but the structure is still used to store data
+ * needed by the cancellation cleanup handler.
+ */
+
+struct waiter {
+	struct waiter *prev, *next;
+	volatile int state, barrier;
+	volatile int *notify;
 };
 
-static void unwait(pthread_cond_t *c, pthread_mutex_t *m)
-{
-	/* Removing a waiter is non-trivial if we could be using requeue
-	 * based broadcast signals, due to mutex access issues, etc. */
+/* Self-synchronized-destruction-safe lock functions */
 
-	if (c->_c_mutex == (void *)-1) {
-		a_dec(&c->_c_waiters);
-		return;
+static inline void lock(volatile int *l)
+{
+	if (a_cas(l, 0, 1)) {
+		a_cas(l, 1, 2);
+		do __wait(l, 0, 2, 1);
+		while (a_cas(l, 0, 2));
 	}
+}
 
-	while (a_swap(&c->_c_lock, 1))
-		__wait(&c->_c_lock, &c->_c_lockwait, 1, 1);
-
-	if (c->_c_waiters) c->_c_waiters--;
-	else a_dec(&m->_m_waiters);
-
-	a_store(&c->_c_lock, 0);
-	if (c->_c_lockwait) __wake(&c->_c_lock, 1, 1);
+static inline void unlock(volatile int *l)
+{
+	if (a_swap(l, 0)==2)
+		__wake(l, 1, 1);
 }
 
-static void cleanup(void *p)
+static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
 {
-	struct cm *cm = p;
-	unwait(cm->c, cm->m);
-	pthread_mutex_lock(cm->m);
+	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);
 }
 
-int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct timespec *ts)
+enum {
+	WAITING,
+	SIGNALED,
+	LEAVING,
+};
+
+int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
 {
-	struct cm cm = { .c=c, .m=m };
-	int r, e=0, seq;
+	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;
 
 	if (ts && ts->tv_nsec >= 1000000000UL)
 		return EINVAL;
 
-	pthread_testcancel();
+	__pthread_testcancel();
 
-	if (c->_c_mutex == (void *)-1) {
+	if (c->_c_shared) {
+		shared = 1;
+		fut = &c->_c_seq;
+		seq = c->_c_seq;
 		a_inc(&c->_c_waiters);
 	} else {
-		c->_c_mutex = m;
-		while (a_swap(&c->_c_lock, 1))
-			__wait(&c->_c_lock, &c->_c_lockwait, 1, 1);
-		c->_c_waiters++;
-		a_store(&c->_c_lock, 0);
-		if (c->_c_lockwait) __wake(&c->_c_lock, 1, 1);
+		lock(&c->_c_lock);
+
+		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;
+		else node.next->prev = &node;
+
+		unlock(&c->_c_lock);
 	}
 
-	seq = c->_c_seq;
+	__pthread_mutex_unlock(m);
 
-	if ((r=pthread_mutex_unlock(m))) return r;
+	__pthread_setcancelstate(PTHREAD_CANCEL_MASKED, &cs);
+	if (cs == PTHREAD_CANCEL_DISABLE) __pthread_setcancelstate(cs, 0);
 
-	do e = __timedwait(&c->_c_seq, seq, c->_c_clock, ts, cleanup, &cm, 0);
-	while (c->_c_seq == seq && (!e || e==EINTR));
+	do e = __timedwait_cp(fut, seq, clock, ts, !shared);
+	while (*fut==seq && (!e || e==EINTR));
 	if (e == EINTR) e = 0;
 
-	unwait(c, m);
+	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. */
+
+		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 ((r=pthread_mutex_lock(m))) return r;
+	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, *first=0;
+	volatile int ref = 0;
+	int cur;
+
+	lock(&c->_c_lock);
+	for (p=c->_c_tail; n && p; p=p->prev) {
+		if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
+			ref++;
+			p->notify = &ref;
+		} else {
+			n--;
+			if (!first) first=p;
+		}
+	}
+	/* Split the list, leaving any remainder on the cv. */
+	if (p) {
+		if (p->next) p->next->prev = 0;
+		p->next = 0;
+	} else {
+		c->_c_head = 0;
+	}
+	c->_c_tail = p;
+	unlock(&c->_c_lock);
+
+	/* Wait for any waiters in the LEAVING state to remove
+	 * themselves from the list before returning or allowing
+	 * signaled threads to proceed. */
+	while ((cur = ref)) __wait(&ref, 0, cur, 1);
+
+	/* Allow first signaled waiter, if any, to proceed. */
+	if (first) unlock(&first->barrier);
+
+	return 0;
+}
+
+weak_alias(__pthread_cond_timedwait, pthread_cond_timedwait);