Difference between CyclicBarrier and CountDownLatch?

By | March 5, 2023

CyclicBarrier and CountDownLatch are both synchronization constructs provided by the Java concurrency framework, but they have some important differences in their behavior and usage.

CountDownLatch is used to wait for a fixed number of events to occur before continuing execution. It is initialized with a count, and each time an event occurs, the count is decremented. Threads can wait for the count to reach zero by calling the await() method. Once the count reaches zero, all waiting threads are released and can continue execution.

On the other hand, CyclicBarrier is used to synchronize a group of threads that need to wait for each other to reach a certain point before continuing execution. It is initialized with a count and a barrier action, and threads can wait for the other threads to arrive at the barrier by calling the await() method. Once the specified number of threads have arrived at the barrier, the barrier action is executed and all threads are released to continue execution.

Here are some key differences between CyclicBarrier and CountDownLatch:

  1. Reusability: A CountDownLatch cannot be reused once its count has reached zero, whereas a CyclicBarrier can be reset and used again.
  2. Number of events: A CountDownLatch is used to synchronize one or more threads with a fixed number of events, whereas a CyclicBarrier is used to synchronize a fixed number of threads.
  3. Barrier action: A CyclicBarrier can be initialized with a barrier action that is executed once all threads have arrived at the barrier, whereas a CountDownLatch does not have this feature.
  4. Waiting threads: In a CountDownLatch, waiting threads are released once the count reaches zero, whereas in a CyclicBarrier, waiting threads are released once the specified number of threads have arrived at the barrier.
  5. Exceptions: A CyclicBarrier can throw a BrokenBarrierException if one of the waiting threads is interrupted or times out, whereas a CountDownLatch does not have this exception.

In summary, CountDownLatch is used to synchronize one or more threads with a fixed number of events, while CyclicBarrier is used to synchronize a fixed number of threads that need to wait for each other to reach a certain point before continuing execution.

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