CountDownLatch 和 CyclicBarrier 的用法

阿新 • • 發佈：2019-12-31

CountDownLatch

作用：是一組執行緒等待其他的執行緒完成工作以後在執行，加強版join

await 用來等待，countDown 負責計數器的減一

public class UseCountDownLatch {
	
	static CountDownLatch latch = new CountDownLatch(6);

    /**
     * 初始化執行緒(只有一步，有4個)
     */
    private static class InitThread implements Runnable{

        @Override
        public void 
 run() {
            System.out.println("Thread_" + Thread.currentThread().getId() + " ready init work......");
            //初始化執行緒完成工作了，countDown方法只扣減一次；
        	latch.countDown();
            for(int i =0;i<2;i++) {
            	System.out.println("Thread_"+Thread.currentThread().getId() +" ........continue do its work" 
);
            }
        }
    }
    
    //業務執行緒
    private static class BusiThread implements Runnable{

        @Override
        public void run() {
        	try {
				latch.await();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
            for(int i =0;i<3;i++) {
            	System.out.println("BusiThread_" 
+Thread.currentThread().getId()
            			+" do business-----");
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new Thread(new BusiThread()).start();
        for(int i=0;i<=3;i++){
            Thread thread = new Thread(new InitThread());
            thread.start();
        }

        latch.await();
        System.out.println("Main done its work........");
    }
}

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CyclicBarrier

讓一組執行緒達到某個屏障，被阻塞，一直到組內最後一個執行緒達到屏障時，屏障開放，所有被阻塞的執行緒會繼續執行

CyclicBarrier(int parties) CyclicBarrier(int parties,Runnable barrierAction)，屏障開放，barrierAction 定義的任務會執行

public class UseCyclicBarrier {
	
	private static CyclicBarrier barrier = new CyclicBarrier(5,new CollectThread());

    /**
     * 存放子執行緒工作結果的容器
     */
    private static ConcurrentHashMap<String,Long> resultMap = new ConcurrentHashMap<>();

    public static void main(String[] args) {
        for(int i=0;i<=4;i++){
            Thread thread = new Thread(new SubThread());
            thread.start();
        }

    }

    /**
     * 負責屏障開放以後的工作
     */
    private static class CollectThread implements Runnable{

        @Override
        public void run() {
            StringBuilder result = new StringBuilder();
            for(Map.Entry<String,Long> workResult:resultMap.entrySet()){
            	result.append("[").append(workResult.getValue()).append("]");
            }
            System.out.println(" the result = "+ result);
            System.out.println("do other business........");
        }
    }

    /**
     * 工作執行緒
     */
    private static class SubThread implements Runnable{

        @Override
        public void run() {
        	long id = Thread.currentThread().getId();
            resultMap.put(Thread.currentThread().getId() + "",id);
            //隨機決定工作執行緒的是否睡眠
            Random r = new Random();
            try {
                if(r.nextBoolean()) {
                	Thread.sleep(2000+id);
                	System.out.println("Thread_"+id+" ....do something ");
                }
                System.out.println(id+"....is await");
                barrier.await();
            	Thread.sleep(1000+id);
                System.out.println("Thread_"+id+" ....do its business ");
            } catch (Exception e) {
                e.printStackTrace();
            }

        }
    }
}

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