Java.util.concurrent Synchronizers

Internal

• java.util.concurrent

CountDownLatch

External

• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CountDownLatch.html

Overview

A CountDownLatch is a synchronization tool that allows one or more threads to wait on it until a certain number of operations being performed in other threads completes. The latch is initialized with a count. Any thread calling await() blocks unit the count reaches zero, after which it is released. You can think of those threads as waiting on a gate to open. The count is decremented with countDown(), which can be called in a loop from a single thread, or concurrently from multiple threads. Note that the threads invoking countDown() are not blocked on the latch - they decrement and continue.

Once the count reached zero, the latch cannot be reused. If you need a reusable mechanism, use Cyclic Barrier.