+
+ m = c->_c_mutex;
+
+ /* If mutex ptr is not available, simply wake all waiters. */
+ if (m == (void *)-1) {
+ unlock(c);
+ __wake(&c->_c_block, -1, 0);
+ return 0;
+ }
+
+ /* Move waiter count to the mutex */
+ for (;;) {
+ w = c->_c_waiters;
+ a_fetch_add(&m->_m_waiters, w);
+ if (a_cas(&c->_c_waiters, w, 0) == w) break;
+ a_fetch_add(&m->_m_waiters, -w);
+ }
+
+ /* Perform the futex requeue, waking one waiter if and only if
+ * the calling thread does not hold the mutex. */
+ __syscall(SYS_futex, &c->_c_block, FUTEX_REQUEUE,
+ m->_m_lock!=pthread_self()->tid, INT_MAX, &m->_m_lock);
+
+ unlock(c);