The type of counting semaphores.

make n returns a new counting semaphore, with initial value n. The initial value n must be nonnegative.

• raises Invalid_argument

  if n < 0

release s increments the value of semaphore s. If other threads are waiting on s, one of them is restarted. If the current value of s is equal to max_int, the value of the semaphore is unchanged and a Sys_error exception is raised to signal overflow.

• raises Sys_error

  if the value of the semaphore would overflow max_int

acquire s blocks the calling thread until the value of semaphore s is not zero, then atomically decrements the value of s and returns.

try_acquire s immediately returns false if the value of semaphore s is zero. Otherwise, the value of s is atomically decremented and try_acquire s returns true.

get_value s returns the current value of semaphore s. The current value can be modified at any time by concurrent release and acquire operations. Hence, the get_value operation is racy, and its result should only be used for debugging or informational messages.