1 files changed, 21 insertions, 0 deletions
diff --git a/src/thread/sem_post.c b/src/thread/sem_post.c
new file mode 100644
index 0000000..5c2517f
--- /dev/null
+++ b/src/thread/sem_post.c
@@ -0,0 +1,21 @@
+#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;
+}