optimize cond waiter move using atomic swap instead of cas loop

[musl] / src / thread / pthread_cond_timedwait.c

diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index 228f61f..9616dd8 100644 (file)
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -1,26 +1,57 @@
 #include "pthread_impl.h"
 
-static void relock(void *m)
+struct cm {
+       pthread_cond_t *c;
+       pthread_mutex_t *m;
+};
+
+static void unwait(pthread_cond_t *c, pthread_mutex_t *m)
+{
+       int w;
+
+       /* Cannot leave waiting status if there are any live broadcasters
+        * which might be inspecting/using the mutex. */
+       while ((w=c->_c_bcast)) __wait(&c->_c_bcast, &c->_c_leavers, w, 0);
+
+       /* If the waiter count is zero, it must be the case that the
+        * caller's count has been moved to the mutex due to bcast. */
+       do w = c->_c_waiters;
+       while (w && a_cas(&c->_c_waiters, w, w-1)!=w);
+       if (!w) a_dec(&m->_m_waiters);
+}
+
+static void cleanup(void *p)
 {
-       pthread_mutex_lock(m);
+       struct cm *cm = p;
+       unwait(cm->c, cm->m);
+       pthread_mutex_lock(cm->m);
 }
 
 int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct timespec *ts)
 {
-       int r, e=0;
-       CANCELPT(0);
+       struct cm cm = { .c=c, .m=m };
+       int r, e, tid;
+
+       if (ts && ts->tv_nsec >= 1000000000UL)
+               return EINVAL;
+
+       pthread_testcancel();
+
+       if (c->_c_mutex != (void *)-1) c->_c_mutex = m;
+
+       a_inc(&c->_c_waiters);
+       c->_c_block = tid = pthread_self()->tid;
 
-       pthread_cleanup_push(relock, m);
-       c->_c_block = 1;
        if ((r=pthread_mutex_unlock(m))) return r;
 
-       CANCELPT(1);
-       e = __timedwait(&c->_c_block, 1, c->_c_clock, ts, 0);
-       CANCELPT(0);
+       do e = __timedwait(&c->_c_block, tid, c->_c_clock, ts, cleanup, &cm, 0);
+       while (c->_c_block == tid && (!e || e==EINTR));
+       if (e == EINTR) e = 0;
+
+       unwait(c, m);
 
-       pthread_cleanup_pop(0);
        if ((r=pthread_mutex_lock(m))) return r;
 
-       CANCELPT(0);
+       pthread_testcancel();
        return e;
 }