third_party/musl/src/thread/sem_post.c

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

int sem_post(sem_t *sem)
{
	int val, new, waiters, priv = sem->__val[2];
	do {
		val = sem->__val[0];
		waiters = sem->__val[1];
		if ((val & SEM_VALUE_MAX) == SEM_VALUE_MAX) {
			errno = EOVERFLOW;
			return -1;
		}
		new = val + 1;
		if (waiters <= 1)
			new &= ~0x80000000;
	} while (a_cas(sem->__val, val, new) != val);
	if (val<0) __wake(sem->__val, waiters>1 ? 1 : -1, priv);
	return 0;
}