package containers

A semaphore

create n creates a semaphore with initial value n

• raises Invalid_argument

  if n < 0

Current value

acquire n s blocks until get s > n, then atomically sets s := !s - n

release n s atomically sets s := !s + n

with_acquire ~n s ~f first acquires s with n units, calls f (), and then release s with n units. Safely release the semaphore even if f () fails

wait_until_at_least ~n s ~f waits until get s >= n, then calls f () and returns its result. Doesn't modify the semaphore.