java当我运行此代码时，应用程序不会终止

Question

public class Threaddemo {

public static void main(String[] args) throws InterruptedException {

Object obj1 = new Object();

Object obj2 = new Object();

Object obj3 = new Object();

Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1");

Thread t2 = new Thread(new SyncThread(obj2, obj3), "t2");

Thread t3 = new Thread(new SyncThread(obj3, obj1), "t3");

t1.start();

Thread.sleep(500);

t2.start();

Thread.sleep(500);

t3.start();

}

}

class SyncThread implements Runnable{

private Object obj1;

private Object obj2;

public SyncThread(Object o1, Object o2){

this.obj1=o1;

this.obj2=o2;

}

@Override

public void run() {

String name = Thread.currentThread().getName();

System.out.println(name + " acquiring lock on "+obj1);

synchronized (obj1) {

System.out.println(name + " acquired lock on "+obj1);

work();

System.out.println(name + " acquiring lock on "+obj2);

synchronized (obj2) {

System.out.println(name + " acquired lock on "+obj2);

work();

}

System.out.println(name + " released lock on "+obj2);

}

System.out.println(name + " released lock on "+obj1);

System.out.println(name + " finished execution.");

}

private void work() {

try {

Thread.sleep(30000);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

Answer 1

你遇到了僵局问题

t1 aquires锁定obj1。然后做一些工作。同时，t2 aquires锁定obj2并进行一些工作。t3和obj3也是如此

现在t1完成了它的第一项工作，希望获得obj2的锁。它必须等待t2完成obj2。但t2正在等待t3完成并从obj3释放锁。另一方面，如果t3已经锁定了obj1，则t3只会从obj3释放锁，而obj1被t1锁定

所以每个人都在等待另一个完成。这基本上就是三线程死锁的定义

您可以在输出中看到这一点：

t1 acquiring lock on java.lang.Object@78f92cc8                                                                                                                                                                                    
t1 acquired lock on java.lang.Object@78f92cc8                                                                                                                                                                                     
t2 acquiring lock on java.lang.Object@55d2162c                                                                                                                                                                                    
t2 acquired lock on java.lang.Object@55d2162c                                                                                                                                                                                     
t3 acquiring lock on java.lang.Object@47122d                                                                                                                                                                                      
t3 acquired lock on java.lang.Object@47122d                                                                                                                                                                                       
t1 acquiring lock on java.lang.Object@55d2162c (<  waiting for t2 to finish)                                                                                                                                                                                    
t2 acquiring lock on java.lang.Object@47122d (< waiting for t3 to finish)                                                                                                                                                                                      
t3 acquiring lock on java.lang.Object@78f92cc8 (<  waiting for t1 to finish)

希望我能帮助你

问候， 克里斯