A CountDownLatch expects count calls to count_down/2 before calls to await/2 can continue.

A CountDownLatch is initialized with a count.

await/2 blocks until the current count reaches 0 due to invocations of the count_down/2 method, after which all blocked processes are unblocked.

Any subsequent invocations of await/2 return immediately. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a SyncPrimitives.CyclicBarrier.

Example

iex> latch = SyncPrimitives.CountDownLatch.start(2, fn -> IO.puts("latch done") end)
{SyncPrimitives.CountDownLatch, #PID<0.227.0>}
iex> spawn_link(fn ->
...>  IO.puts("before wait")
...>  SyncPrimitives.CountDownLatch.await(latch)
...>  IO.puts("after wait")
...> end)
before wait
#PID<0.233.0>
iex> # nothing happens for a while
nil
iex> SyncPrimitives.CountDownLatch.count_down(latch)
:ok
iex> SyncPrimitives.CountDownLatch.count_down(latch)
latch done
after wait
:ok
iex> SyncPrimitives.CountDownLatch.stop(latch)
:ok