Java| CountdownLatch | CyclicBarrier | |
|---|---|---|
| Đồng bộ | Một chiều, một lần | Cyclic (tái sử dụng) |
| Ai chờ ai | Main thread chờ N worker xong | N thread chờ nhau cùng tiến |
| Reset | Không | Có (tự reset sau mỗi vòng) |
java
// CountdownLatch — main chờ N worker xong
CountDownLatch latch = new CountDownLatch(3);
for (int i = 0; i < 3; i++) {
new Thread(() -> {
doWork();
latch.countDown();
}).start();
}
latch.await(); // block đến khi counter = 0
// CyclicBarrier — N thread đồng bộ tại checkpoint
CyclicBarrier barrier = new CyclicBarrier(3, () -> System.out.println("all here"));
for (int i = 0; i < 3; i++) {
new Thread(() -> {
phase1();
barrier.await(); // chờ 2 thread khác
phase2();
}).start();
}Dùng: CountdownLatch cho one-shot wait (start N service rồi mới ready); CyclicBarrier cho phased coordination (chia work theo round, mỗi round đồng bộ).
| CountdownLatch | CyclicBarrier | |
|---|---|---|
| Sync | One-way, one-shot | Cyclic (reusable) |
| Who waits whom | Main waits for N workers | N threads wait for each other |
| Reset | No | Yes (auto resets each round) |
java
// CountdownLatch — main waits for N workers
CountDownLatch latch = new CountDownLatch(3);
for (int i = 0; i < 3; i++) {
new Thread(() -> {
doWork();
latch.countDown();
}).start();
}
latch.await(); // blocks until counter hits 0
// CyclicBarrier — N threads synchronise at a checkpoint
CyclicBarrier barrier = new CyclicBarrier(3, () -> System.out.println("all here"));
for (int i = 0; i < 3; i++) {
new Thread(() -> {
phase1();
barrier.await(); // waits for the other 2 threads
phase2();
}).start();
}Use: CountdownLatch for one-shot waits (start N services before ready); CyclicBarrier for phased coordination (split work into rounds, sync each round).