死锁知识点

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什么是死锁

两个线程分别是线程1和线程2。线程1执行过程中，先获得对象a的锁，然后要再获得b的锁才能继续执行代码；而线程2正巧相反，先获得对象b的锁，然后要再获得a的锁才能继续执行代码。这时，两个线程都等着对方解锁，才能继续执行，这时，两个线程就进入等待状态，最终不会有线程执行。这就变成了死锁。

简单的死锁代码

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public class DeadLockTest implements Algorithm {
    public Object object1 = new Object();
    public Object object2 = new Object();

    @Override
    public void execut() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                Utils.printString("=====>>thread 1 running");
                Lock1.test();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                Utils.printString("=====>>thread 2 running");
                Lock2.test();
            }
        }).start();
    }

    public static class Lock1 {
        public static synchronized void test(){
            try {
                Utils.printString(Thread.currentThread().getName() + " get lock1");
                Thread.sleep(500);
                Utils.printString(Thread.currentThread().getName() + " try to get lock2");
                Lock2.test();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    public static class Lock2 {
        public static synchronized void test(){
            try {
                Utils.printString(Thread.currentThread().getName() + " get lock2");
                Thread.sleep(1000);
                Utils.printString(Thread.currentThread().getName() + " try to get lock1");
                Lock1.test();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

运行结果

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=====>>thread 1 running
=====>>thread 2 running
Thread-0 get lock1
Thread-1 get lock2
Thread-0 try to get lock2
Thread-1 try to get lock1