X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=blobdiff_plain;f=src%2Fthread%2Fpthread_barrier_wait.c;h=db432ba30a21bf1b30c8bbd52daaad387b6271d5;hp=7bfadb9532195bfad63561032e5e3f2fde376f12;hb=60164570111873175111cf8a5b973375e492eee9;hpb=e882756311c7b06e59fcc8e582f03852b7dcfd30

diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index 7bfadb95..db432ba3 100644
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,31 +1,118 @@
 #include "pthread_impl.h"
 
+static int vmlock[2];
+
+void __vm_lock(int inc)
+{
+	for (;;) {
+		int v = vmlock[0];
+		if (inc*v < 0) __wait(vmlock, vmlock+1, v, 1);
+		else if (a_cas(vmlock, v, v+inc)==v) break;
+	}
+}
+
+void __vm_unlock(void)
+{
+	if (vmlock[0]>0) a_dec(vmlock);
+	else a_inc(vmlock);
+	if (vmlock[1]) __wake(vmlock, 1, 1);
+}
+
+static int pshared_barrier_wait(pthread_barrier_t *b)
+{
+	int limit = (b->_b_limit & INT_MAX) + 1;
+	int seq;
+	int ret = 0;
+
+	if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+	while (a_swap(&b->_b_lock, 1))
+		__wait(&b->_b_lock, &b->_b_waiters, 1, 0);
+
+	seq = b->_b_seq;
+
+	if (++b->_b_count == limit) {
+		ret = PTHREAD_BARRIER_SERIAL_THREAD;
+		b->_b_seq++;
+		__wake(&b->_b_seq, -1, 0);
+	} else {
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+		__wait(&b->_b_seq, 0, seq, 0);
+	}
+
+	__vm_lock(+1);
+
+	if (a_fetch_add(&b->_b_count, -1)==1) {
+		b->_b_seq++;
+		__wake(&b->_b_seq, -1, 0);
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+	} else {
+		__wait(&b->_b_seq, 0, seq+1, 0);
+	}
+	
+	__vm_unlock();
+
+	return 0;
+}
+
+struct instance
+{
+	int count;
+	int last;
+	int waiters;
+	int finished;
+};
+
 int pthread_barrier_wait(pthread_barrier_t *b)
 {
-	int cur;
+	int limit = b->_b_limit;
+	struct instance *inst;
 
 	/* Trivial case: count was set at 1 */
-	if (!b->_b_limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+	if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+	/* Process-shared barriers require a separate, inefficient wait */
+	if (limit < 0) return pshared_barrier_wait(b);
 
-	/* Wait for anyone still suspended at previous use of barrier */
-	while ((cur=b->_b_left))
-		__wait(&b->_b_left, &b->_b_waiters, cur, 0);
+	/* Otherwise we need a lock on the barrier object */
+	while (a_swap(&b->_b_lock, 1))
+		__wait(&b->_b_lock, &b->_b_waiters, 1, 1);
+	inst = b->_b_inst;
 
-	/* If we are the last to reach barrier, reset it and wake others */
-	if (a_fetch_add(&b->_b_count, 1) == b->_b_limit) {
-		b->_b_left = b->_b_limit;
-		b->_b_count = 0;
-		__wake(&b->_b_count, -1, 0);
+	/* First thread to enter the barrier becomes the "instance owner" */
+	if (!inst) {
+		struct instance new_inst = { 0 };
+		int spins = 10000;
+		b->_b_inst = inst = &new_inst;
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
+		while (spins-- && !inst->finished)
+			a_spin();
+		a_inc(&inst->finished);
+		while (inst->finished == 1)
+			__syscall(SYS_futex, &inst->finished, FUTEX_WAIT,1,0);
 		return PTHREAD_BARRIER_SERIAL_THREAD;
 	}
 
-	/* Wait for our peers to reach the barrier */
-	while ((cur=b->_b_count))
-		__wait(&b->_b_count, 0, cur, 0);
+	/* Last thread to enter the barrier wakes all non-instance-owners */
+	if (++inst->count == limit) {
+		b->_b_inst = 0;
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
+		a_store(&inst->last, 1);
+		if (inst->waiters)
+			__wake(&inst->last, -1, 1);
+	} else {
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
+		__wait(&inst->last, &inst->waiters, 0, 1);
+	}
 
-	/* If we're the last to wake up and barrier is awaiting reuse */
-	if (a_fetch_add(&b->_b_left, -1) == 1 && b->_b_waiters)
-		__wake(&b->_b_left, -1, 0);
+	/* Last thread to exit the barrier wakes the instance owner */
+	if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
+		__wake(&inst->finished, 1, 1);
 
 	return 0;
 }