DCL双检查机制

DCL双检查锁机制

双检查锁就是在同步代码块调用之前检查一遍，载再在同步代码块内部再检查一遍。双重保险

public class ServiceA {private volatile static ServiceA service;private ServiceA(){}public stati<span id="_xhe_cursor"></span>c ServiceA getInstance(){try{if(service != null){}else{Thread.sleep(3000);synchronized(ServiceA.class){if(service == null){service = new ServiceA();}}}}catch(InterruptedException e){e.printStackTrace();}return service;}public static void main(String[] args) {MyThread t1 = new MyThread();MyThread t2 = new MyThread();MyThread t3 = new MyThread();t1.start();t2.start();t3.start();}}class MyThread extends Thread{public void run(){System.out.println(ServiceA.getInstance().hashCode());}}