As per java doc , a synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.
A CountDownLatch is initialized with a given count.
The #await 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 await 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 CyclicBarrier.
A code 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.
A useful property of a CountDownLatch is that it
doesn't require that threads calling countDown wait for
the count to reach zero before proceeding, it simply prevents any
thread from proceeding past an await until all
threads could pass.
CountDownLatch Example with code snippet