eliminate global waiters count in pthread_once

diff --git a/src/thread/pthread_once.c b/src/thread/pthread_once.c
index b7388b9..7c47385 100644 (file)
--- a/src/thread/pthread_once.c
+++ b/src/thread/pthread_once.c
@@ -2,14 +2,14 @@
 
 static void undo(void *control)
 {
-       a_store(control, 0);
-       __wake(control, 1, 1);
+       /* Wake all waiters, since the waiter status is lost when
+        * resetting control to the initial state. */
+       if (a_swap(control, 0) == 3)
+               __wake(control, -1, 1);
 }
 
 int __pthread_once(pthread_once_t *control, void (*init)(void))
 {
-       static int waiters;
-
        /* Return immediately if init finished before, but ensure that
         * effects of the init routine are visible to the caller. */
        if (*control == 2) {
@@ -17,10 +17,11 @@ int __pthread_once(pthread_once_t *control, void (*init)(void))
                return 0;
        }
 
-       /* Try to enter initializing state. Three possibilities:
+       /* Try to enter initializing state. Four possibilities:
         *  0 - we're the first or the other cancelled; run init
         *  1 - another thread is running init; wait
-        *  2 - another thread finished running init; just return */
+        *  2 - another thread finished running init; just return
+        *  3 - another thread is running init, waiters present; wait */
 
        for (;;) switch (a_cas(control, 0, 1)) {
        case 0:
@@ -28,11 +29,14 @@ int __pthread_once(pthread_once_t *control, void (*init)(void))
                init();
                pthread_cleanup_pop(0);
 
-               a_store(control, 2);
-               if (waiters) __wake(control, -1, 1);
+               if (a_swap(control, 2) == 3)
+                       __wake(control, -1, 1);
                return 0;
        case 1:
-               __wait(control, &waiters, 1, 1);
+               /* If this fails, so will __wait. */
+               a_cas(control, 1, 3);
+       case 3:
+               __wait(control, 0, 3, 1);
                continue;
        case 2:
                return 0;