#java.util.concurrent.CountDownLatch – a more general wait/notify mechanism
A synchronization aid that allows one or more threads to wait until a
set of operations being performed in other threads completes.
initialized with a given count.
The await methods block until the current count reaches zero due to
invocations of the countDown() method, after which all waiting threads
are released and any subsequent invocations of await return
This is a one-shot phenomenon – the count cannot be reset. If you need a version that resets the count, consider using a
A CountDownLatch is a versatile synchronization tool and can be used for a number of purposes.
- A CountDownLatch initialized with a count of one serves as a simple on/off latch, or gate: all threads invoking await wait at the gate until it is opened by a thread invoking countDown().
- A CountDownLatch initialized to N can be used to make one thread wait until N threads have completed some action, or some action has been completed N times.