fix some semaphore wait semantics (race condition deadlock and error checking)

[musl] / src / thread / sem_trywait.c

diff --git a/src/thread/sem_trywait.c b/src/thread/sem_trywait.c
index d0e928e..c5370c7 100644 (file)
--- a/src/thread/sem_trywait.c
+++ b/src/thread/sem_trywait.c
@@ -5,7 +5,8 @@ int sem_trywait(sem_t *sem)
 {
        int val = a_fetch_add(sem->__val, -1);
        if (val > 0) return 0;
-       a_inc(sem->__val);
+       if (!a_fetch_add(sem->__val, 1))
+               __wake(sem->__val, 1, 0);
        errno = EAGAIN;
        return -1;
 }