Java死锁程序(一)

来源：互联网发布：mac系统做淘宝编辑：程序博客网时间：2024/05/22 15:50

思路是创建两个字符串a和b，再创建两个线程A和B，让每个线程都用synchronized锁住字符串（A先锁a，再去锁b；B先锁b，再锁a），如果A锁住a，B锁住b，A就没办法锁住b，B也没办法锁住a，这时就陷入了死锁。直接贴代码：

public class DeadLock {    public static String obj1 = "obj1";    public static String obj2 = "obj2";    public static void main(String[] args){        Thread a = new Thread(new Lock1());        Thread b = new Thread(new Lock2());        a.start();        b.start();    }    }class Lock1 implements Runnable{    @Override    public void run(){        try{            System.out.println("Lock1 running");            while(true){                synchronized(DeadLock.obj1){                    System.out.println("Lock1 lock obj1");                    Thread.sleep(3000);//获取obj1后先等一会儿，让Lock2有足够的时间锁住obj2                    synchronized(DeadLock.obj2){                        System.out.println("Lock1 lock obj2");                    }                }            }        }catch(Exception e){            e.printStackTrace();        }    }}class Lock2 implements Runnable{    @Override    public void run(){        try{            System.out.println("Lock2 running");            while(true){                synchronized(DeadLock.obj2){                    System.out.println("Lock2 lock obj2");                    Thread.sleep(3000);                    synchronized(DeadLock.obj1){                        System.out.println("Lock2 lock obj1");                    }                }            }        }catch(Exception e){            e.printStackTrace();        }    }}

运行的结果如图所示：

可以看到，Lock1获取obj1，Lock2获取obj2，但是它们都没有办法再获取另外一个obj，因为它们都在等待对方先释放锁，这时就是死锁。

如果我们只运行Lock1呢？修改一下main函数，把线程b注释掉。

public class DeadLock {    public static String obj1 = "obj1";    public static String obj2 = "obj2";    public static void main(String[] args){        Thread a = new Thread(new Lock1());        //Thread b = new Thread(new Lock2());        a.start();        //b.start();    }}class Lock1 implements Runnable{    @Override    public void run(){        try{            System.out.println("Lock1 running");            while(true){                synchronized(DeadLock.obj1){                    System.out.println("Lock1 lock obj1");                    Thread.sleep(3000);                    synchronized(DeadLock.obj2){                        System.out.println("Lock1 lock obj2");                    }                }            }        }catch(Exception e){            e.printStackTrace();        }    }}class Lock2 implements Runnable{    @Override    public void run(){        try{            System.out.println("Lock2 running");            while(true){                synchronized(DeadLock.obj2){                    System.out.println("Lock2 lock obj2");                    Thread.sleep(3000);                    synchronized(DeadLock.obj1){                        System.out.println("Lock2 lock obj1");                    }                }            }        }catch(Exception e){            e.printStackTrace();        }    }}

运行结果为：

由于没有其它线程和Lock1争夺obj1和obj2，Lock1可以不断地循环获取并释放它们，这时没有死锁。

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