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 releases 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.