overhaul posix semaphores to fix destructability race

[musl] / src / thread / sem_post.c

#include <semaphore.h>
#include "pthread_impl.h"

int sem_post(sem_t *sem)
{
        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;
}