CountDownLatches

CountDownLatch is a synchronization aid in Java's java.util.concurrent package. It allows one or more threads to wait until a set of operations being performed in other threads completes. The CountDownLatch is 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 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.

CountDownLatch is typically used to coordinate the start and end of a set of tasks. For example, a main thread can create a CountDownLatch with a count equal to the number of worker threads. Each worker thread can then call countDown once it has completed its task. The main thread can then call await, which will block until all worker threads have called countDown. This ensures that the main thread does not proceed until all worker threads have completed their tasks.

CountDownLatch can also be used to coordinate the start of a set of tasks. For example, a main thread can create a CountDownLatch with a count of one. The main thread can then start all worker threads and call countDown once they have all been started. Each worker thread can then call await, which will block until the main thread calls countDown. This ensures that all worker threads do not proceed until the main thread has started them.

CountDownLatch is a versatile synchronization aid that can be used in a variety of scenarios. It is important to use CountDownLatch correctly to avoid deadlocks and other synchronization issues. It is also important to consider the performance implications of using CountDownLatch, as it can introduce overhead in some scenarios.