+/**
+ * Initializes a semaphore.
+ */
+void vlc_sem_init (vlc_sem_t *sem, unsigned value)
+{
+#if defined(__APPLE__)
+ if (unlikely(semaphore_create(mach_task_self(), sem, SYNC_POLICY_FIFO, value) != KERN_SUCCESS))
+ abort ();
+#else
+ if (unlikely(sem_init (sem, 0, value)))
+ abort ();
+#endif
+}
+
+/**
+ * Destroys a semaphore.
+ */
+void vlc_sem_destroy (vlc_sem_t *sem)
+{
+ int val;
+
+#if defined(__APPLE__)
+ if (likely(semaphore_destroy(mach_task_self(), *sem) == KERN_SUCCESS))
+ return;
+
+ val = EINVAL;
+#else
+ if (likely(sem_destroy (sem) == 0))
+ return;
+
+ val = errno;
+#endif
+
+ VLC_THREAD_ASSERT ("destroying semaphore");
+}
+
+/**
+ * Increments the value of a semaphore.
+ * @return 0 on success, EOVERFLOW in case of integer overflow
+ */
+int vlc_sem_post (vlc_sem_t *sem)
+{
+ int val;
+
+#if defined(__APPLE__)
+ if (likely(semaphore_signal(*sem) == KERN_SUCCESS))
+ return 0;
+
+ val = EINVAL;
+#else
+ if (likely(sem_post (sem) == 0))
+ return 0;
+
+ val = errno;
+#endif
+
+ if (unlikely(val != EOVERFLOW))
+ VLC_THREAD_ASSERT ("unlocking semaphore");
+ return val;
+}
+
+/**
+ * Atomically wait for the semaphore to become non-zero (if needed),
+ * then decrements it.
+ */
+void vlc_sem_wait (vlc_sem_t *sem)
+{
+ int val;
+
+#if defined(__APPLE__)
+ if (likely(semaphore_wait(*sem) == KERN_SUCCESS))
+ return;
+
+ val = EINVAL;
+#else
+ do
+ if (likely(sem_wait (sem) == 0))
+ return;
+ while ((val = errno) == EINTR);
+#endif
+
+ VLC_THREAD_ASSERT ("locking semaphore");
+}
+