背景
在平時的開發中,我們如何讓各個線程間協調工作呢?
除了我們經常使用的線程同步鎖Sychronized,ReentrantLOcak的使用,還有線程自有方法,sleep,yeid的使用。哪還有那些高級的使用呢?那就是JUC包中的CountDownLatch,CyclicBarrier,Semaphore。今天我們先了解一下CountDownLatch的使用。
CountDownLatch
1. 權威指南
- 一種同步幫助,允許一個或多個線程等待,直到其他線程中執行的一組操作完成爲止。
一個CountDownLatch初始化爲給定數。該await方法將阻塞,直到由於該countDown()方法的調用導致當前計數達到零爲止,此後所有等待線程被釋放,並且隨後的所有awaitreturn 調用都將立即釋放 。這是一種一次性現象-無法重置計數。如果您需要用於重置計數的版本,請考慮使用CyclicBarrier。 - 類介紹
2. 代碼演示
package JUC;
import lombok.Data;
import lombok.SneakyThrows;
import org.omg.PortableServer.THREAD_POLICY_ID;
import java.util.concurrent.CountDownLatch;
/**
* @authoryuanxindong
* @date: 2020/6/16 10:18 下午
*/
public class CountDownLatchDemo implements Runnable{
private static final int DownLatchCount = 3;
private int timeOut;
public CountDownLatchDemo(int timeOut){
this.timeOut = timeOut;
}
static final CountDownLatch latch = new CountDownLatch(DownLatchCount);
public static void main(String[] args) {
// 創建多個線程,且每個線程的sleep的時間是不一致的
CountDownLatchDemo countDownLatchDemo = new CountDownLatchDemo(1000);
Thread thread = new Thread(countDownLatchDemo);
CountDownLatchDemo countDownLatchDemov2 = new CountDownLatchDemo(3000);
Thread thread1 =new Thread(countDownLatchDemov2);
CountDownLatchDemo countDownLatchDemov3 = new CountDownLatchDemo(4000);
Thread thread2 =new Thread(countDownLatchDemov3);
long start = System.currentTimeMillis();
thread.start();
thread1.start();
thread2.start();
try {
System.out.println("等待"+DownLatchCount+"個子線程執行完畢...");
latch.await();
System.out.println(DownLatchCount+"個子線程已經執行完畢");
long time = System.currentTimeMillis()-start;
System.out.println("time:"+ time);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@SneakyThrows
@Override
public void run() {
Thread.sleep(timeOut);
System.out.println("yuanxindongO"+Thread.currentThread().getName());
latch.countDown();
}
}
- 通過啓用三個線程,然後給每個線程一個運行時間通過sleep來控制。分別是1000和3000和4000
- countDownLatch的作用是可以等待所有線程達到執行初始定義的次數,就可以釋放阻塞,接着完成主線程。
- 執行結果:
總結
- 允許一個或多個線程等待某些操作完成(完美!!!!)
參考資料
- https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/CountDownLatch.html
- https://time.geekbang.org/column/article/9373
- https://www.cnblogs.com/dolphin0520/p/3920397.html