java 同步工具類

CountDownLatch

CountDownLatch可以用來保證，一個或者多個線程阻塞在某處，待某些其他指令執行完畢後再開始執行。初始化時指定一個count，程序會在await()方法的掉用處阻塞，每次調用countDown()會使得count減一，當count等於0，await後面的線程將得以執行。值得一提的是，count的值不能重置。

注意，count的值被置爲N，只要通過countDown()的調用將其變爲0，無論是N個線程執行完，還是同一個操作執行了N次，await()方法就不會阻塞。

下面給出一個CountDownLatch的例子。

package syncronizationTool;

import java.util.concurrent.CountDownLatch;

public class TestCountDownLatch {
    public static void main(String [] args) throws Exception {
        int actorNum = 5;
        CountDownLatch startSignal = new CountDownLatch(1);
        CountDownLatch doneSignal = new CountDownLatch(actorNum);
        for(int i = 0; i < actorNum; i++){
            new Thread(new Actor("Actor"+i, startSignal, doneSignal)).start();
        }
        System.out.println("各部門注意，演員請就位，Action~~~");//導演喊Action，各演員開始演戲
        startSignal.countDown();
        System.out.println("拍戲進行中");
        doneSignal.await();
        System.out.println("咔~~~");//導演喊咔，本場演完
    }
}

class Actor implements Runnable {
    private String name;
    private final CountDownLatch startSignal;
    private final CountDownLatch doneSignal;
    Actor(String name, CountDownLatch startSignal, CountDownLatch doneSignal){
        this.name = name;
        this.startSignal = startSignal;
        this.doneSignal = doneSignal;
    }
    @Override
    public void run() {
        try{
            startSignal.await();
            doWork();
            doneSignal.countDown();
        } catch (InterruptedException ie) {

        }
    }
    void doWork(){
        System.out.println(name + " is performing...");
    }
}

CyclicBarraiar

cyclicBarriar用於使一組線程互相等待，直到barriar被打破。固定值N是可以reset的。

例子：

public class TestCyclicBarriar {
    public static void main(String [] args){
        CyclicBarrier barrier = new CyclicBarrier(20, () -> System.out.println("滿人"));

        for(int i = 0; i < 100; i++){
            new Thread(()-> {
                try {
                    barrier.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }).start();
        }
    }
}