Add a "fork" of musl as //fusl.

fusl/src/thread/pthread_barrier_wait.c

Index: fusl/src/thread/pthread_barrier_wait.c
diff --git a/fusl/src/thread/pthread_barrier_wait.c b/fusl/src/thread/pthread_barrier_wait.c
new file mode 100644
index 0000000000000000000000000000000000000000..06b83db9262a56e5b19ba1116f02c389398ea546
--- /dev/null
+++ b/fusl/src/thread/pthread_barrier_wait.c
@@ -0,0 +1,111 @@
+#include "pthread_impl.h"
+
+static int pshared_barrier_wait(pthread_barrier_t *b)
+{
+	int limit = (b->_b_limit & INT_MAX) + 1;
+	int ret = 0;
+	int v, w;
+
+	if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+	while ((v=a_cas(&b->_b_lock, 0, limit)))
+		__wait(&b->_b_lock, &b->_b_waiters, v, 0);
+
+	/* Wait for <limit> threads to get to the barrier */
+	if (++b->_b_count == limit) {
+		a_store(&b->_b_count, 0);
+		ret = PTHREAD_BARRIER_SERIAL_THREAD;
+		if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
+	} else {
+		a_store(&b->_b_lock, 0);
+		if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+		while ((v=b->_b_count)>0)
+			__wait(&b->_b_count, &b->_b_waiters2, v, 0);
+	}
+
+	__vm_lock();
+
+	/* Ensure all threads have a vm lock before proceeding */
+	if (a_fetch_add(&b->_b_count, -1)==1-limit) {
+		a_store(&b->_b_count, 0);
+		if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
+	} else {
+		while ((v=b->_b_count))
+			__wait(&b->_b_count, &b->_b_waiters2, v, 0);
+	}
+	
+	/* Perform a recursive unlock suitable for self-sync'd destruction */
+	do {
+		v = b->_b_lock;
+		w = b->_b_waiters;
+	} while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v);
+
+	/* Wake a thread waiting to reuse or destroy the barrier */
+	if (v==INT_MIN+1 || (v==1 && w))
+		__wake(&b->_b_lock, 1, 0);
+
+	__vm_unlock();
+
+	return ret;
+}
+
+struct instance
+{
+	volatile int count;
+	volatile int last;
+	volatile int waiters;
+	volatile int finished;
+};
+
+int pthread_barrier_wait(pthread_barrier_t *b)
+{
+	int limit = b->_b_limit;
+	struct instance *inst;
+
+	/* Trivial case: count was set at 1 */
+	if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+	/* Process-shared barriers require a separate, inefficient wait */
+	if (limit < 0) return pshared_barrier_wait(b);
+
+	/* 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;
+
+	/* First thread to enter the barrier becomes the "instance owner" */
+	if (!inst) {
+		struct instance new_inst = { 0 };
+		int spins = 200;
+		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|128,1,0) != -ENOSYS
+			|| __syscall(SYS_futex,&inst->finished,FUTEX_WAIT,1,0);
+		return PTHREAD_BARRIER_SERIAL_THREAD;
+	}
+
+	/* 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);
+	}
+
+	/* 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;
+}