overhaul posix semaphores to fix destructability race

[musl] / src / thread / sem_post.c

diff --git a/src/thread/sem_post.c b/src/thread/sem_post.c
index 8f4700c..148ab78 100644 (file)
--- a/src/thread/sem_post.c
+++ b/src/thread/sem_post.c
@@ -3,8 +3,11 @@
 
 int sem_post(sem_t *sem)
 {
 
 int sem_post(sem_t *sem)
 {

-       a_inc(sem->__val);
-       if (sem->__val[1])
-               __wake(sem->__val, 1, 0);
+       int val, waiters;
+       do {
+               val = sem->__val[0];
+               waiters = sem->__val[1];
+       } while (a_cas(sem->__val, val, val+1+(val<0)) != val);
+       if (val<0 || waiters) __wake(sem->__val, 1, 0);

        return 0;
 }
        return 0;
 }