Module Await_sync.Countdown_latch

A Countdown_latch.t is a synchronization aid that allows one or more threads to wait until a number of operations being performed in other threads complete.

A countdown latch is initialized with a count. The await method blocks until a call to decr decrements the count to zero, after which all waiting threads are released. A countdown latch is one-shot -- the count cannot be changed after it reaches zero. If you need a version that resets the count, consider using a Barrier instead, though note that with a barrier the only operation available is waiting - it is not possible to decrement without blocking.

max_count is the maximum allowed count for a countdown latch.

create n returns a new countdown latch with its count initialized to n.

The optional padded argument specifies whether to pad the data structure to avoid false sharing. See Atomic.make for a longer explanation.

• raises Invalid_argument

  if n is negative or greater than max_count.

count t returns the current count of the countdown latch t.

poison t marks the countdown latch as poisoned. Concurrent and subsequent calls to await, await_or_cancel, and incr will raise the Poisoned exception.

is_poisoned t determines whether the countdown latch has been poisoned.

incr t increments the count of the countdown latch t.

The count is not logically modified after it has reached zero.

• raises Poisoned

  if the latch has been poisoned.

• raises Invalid_argument

  in case the latch has already previously reached zero.

decr t decrements the count of the countdown latch t, releasing all waiting threads if the count reaches zero.

The count is not logically modified after it has reached zero.

• raises Invalid_argument

  in case the latch has already previously reached zero.

await w t suspends the caller until the latch t is decremented to zero.

• raises Poisoned

  if the latch has been poisoned.

• raises Terminated

  if w is terminated before the latch reaches zero.

await_or_cancel w c t is Completed () if c is not cancelled or Canceled otherwise

• raises Poisoned

  if the latch has been poisoned.

• raises Terminated

  if w is terminated, even if c is canceled.