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本文小編為大家詳細介紹“Java CountDownLatch計數(shù)器與CyclicBarrier循環(huán)屏障怎么定義”,內(nèi)容詳細,步驟清晰,細節(jié)處理妥當,希望這篇“Java CountDownLatch計數(shù)器與CyclicBarrier循環(huán)屏障怎么定義”文章能幫助大家解決疑惑,下面跟著小編的思路慢慢深入,一起來學(xué)習(xí)新知識吧。
CountDownLatch: A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.
CyclicBarrier: A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point.
上述是Oracle官方定義。簡單來說
CountDownLatch:計數(shù)器,允許一個或多個線程等待,直到在其他線程中執(zhí)行的一組操作完成。
CyclicBarrier:循環(huán)屏障,它允許一組線程相互等待以達到一個共同的屏障點。
區(qū)別
CountDownLatch 是 AQS (AbstractQueuedSynchronizer) 的一員,但 CyclicBarrier 不是。
CountDownLatch 的使用場景中,有兩類線程,一類是調(diào)用await()方法的等待線程,另一類是調(diào)用countDownl() 方法的操作線程。CyclicBarrier 的場景中,只有一類線程,都是相互等待的等待線程。
CountDownLatch 是減計數(shù),遞減完后不能復(fù)位,CyclicBarrier 是加計數(shù),遞增完后自動復(fù)位
創(chuàng)建兩組線程,一組等待另一組執(zhí)行完才繼續(xù)進行
CountDownLatch countDownLatch = new CountDownLatch(5); ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < 5; i++) { executorService.execute(() -> { countDownLatch.countDown(); System.out.println("run.."); }); } for (int i = 0; i < 3; i++) { //我們要等上面執(zhí)行完成才繼續(xù) executorService.execute(() -> { try { countDownLatch.await(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("await.."); }); } executorService.shutdown();
打?。?/p>
run..
run..
run..
run..
run..
await..
await..
await..
等待累加線程執(zhí)行完,主線程再輸出累加結(jié)果
public class ThreadUnsafeExample { private int cnt = 0; public void add() { cnt++; } public int get() { return cnt; } public static void main(String[] args) throws InterruptedException { final int threadSize = 1000; ThreadUnsafeExample example = new ThreadUnsafeExample(); final CountDownLatch countDownLatch = new CountDownLatch(threadSize); ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < threadSize; i++) { executorService.execute(() -> { example.add(); countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); System.out.println(example.get()); } }
打?。?/p>
997
3 模擬并發(fā)
ExecutorService executorService = Executors.newCachedThreadPool(); CountDownLatch countDownLatch = new CountDownLatch(1); for (int i = 0; i < 5; i++) { executorService.submit( () -> { try { countDownLatch.await(); System.out.println("【" + Thread.currentThread().getName() + "】開始執(zhí)行……"); } catch (InterruptedException e) { e.printStackTrace(); } }); } Thread.sleep(2000); countDownLatch.countDown();//開始并發(fā) executorService.shutdown();
打?。?/p>
【pool-2-thread-2】開始執(zhí)行……
【pool-2-thread-5】開始執(zhí)行……
【pool-2-thread-3】開始執(zhí)行……
【pool-2-thread-1】開始執(zhí)行……
【pool-2-thread-4】開始執(zhí)行……
所有線程相互等待,直到某一步完成后再繼續(xù)執(zhí)行
final int totalThread = 3; CyclicBarrier cyclicBarrier = new CyclicBarrier(3); ExecutorService executorService = Executors.newCachedThreadPool(); for (int i = 0; i < totalThread; i++) { executorService.execute(() -> { System.out.println("before.."); try { cyclicBarrier.await(); } catch (InterruptedException | BrokenBarrierException e) { e.printStackTrace(); } System.out.println("after.."); }); } executorService.shutdown();
打印:
before..
before..
before..
after..
after..
after..
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