val make : bool -> t
make b returns a new binary semaphore. If
true, the initial value of the semaphore is 1, meaning "available". If
false, the initial value of the semaphore is 0, meaning "unavailable".
val release : t -> unit
release s sets the value of semaphore
s to 1, putting it in the "available" state. If other threads are waiting on
s, one of them is restarted.
val acquire : t -> unit
acquire s blocks the calling thread until the semaphore
s has value 1 (is available), then atomically sets it to 0 and returns.
val try_acquire : t -> bool
try_acquire s immediately returns
false if the semaphore
s has value 0. If
s has value 1, its value is atomically set to 0 and
try_acquire s returns