Java / Java Concurrency and Multi Threading in Java 17 and Java 21 Interview questions
When should you use CountDownLatch instead of CyclicBarrier?
| CountDownLatch | CyclicBarrier |
| One-time use; count can only decrease and never resets. | Reusable; automatically resets once the barrier trips. |
| Some threads call countDown() while typically different threads call await(). | All participating threads call await() themselves, waiting for each other. |
| Good for "wait until N independent events have happened." | Good for "wait until N threads all reach the same point, then let them all proceed together." |
| No barrier action. | Supports an optional Runnable barrier action run once all parties arrive. |
Use CountDownLatch when the events counting down aren't necessarily symmetric, for example a main thread waiting for several independent worker services to finish initializing before starting the application.
Use CyclicBarrier when a fixed group of worker threads needs to repeatedly synchronize at a shared checkpoint across multiple phases of computation, since it can be reused after each phase completes.
Which synchronizer can be reused across multiple phases automatically?
Which is the better fit for 'wait until 5 independent services finish starting up'?
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