死锁示例

死锁示例

由于两个锁对象lock1,lock2是static只存在一份,导致两个线程执行时会相互等待已经被获得的琐对象,导致死锁产生.
如果将static去掉,2个锁对象就是线程独有的变量,不会被别的线程发现,因此不会产生死锁.

public class DeadLock implements Runnable{
    private String tag;
    private static Object lock1 = new Object();
    private static Object lock2 = new Object();
    
    public void setTag(String tag){
        this.tag = tag;
    }
    
    @Override
    public void run() {
        if(tag.equals("a")){
            synchronized (lock1) {
                try {
                    System.out.println("当前线程 : "  + Thread.currentThread().getName() + " 进入lock1执行");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lock2) {
                    System.out.println("当前线程 : "  + Thread.currentThread().getName() + " 进入lock2执行");
                }
            }
        }
        if(tag.equals("b")){
            synchronized (lock2) {
                try {
                    System.out.println("当前线程 : "  + Thread.currentThread().getName() + " 进入lock2执行");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lock1) {
                    System.out.println("当前线程 : "  + Thread.currentThread().getName() + " 进入lock1执行");
                }
            }
        }
    }
    
    public static void main(String[] args) {
        
        DeadLock d1 = new DeadLock();
        d1.setTag("a");
        DeadLock d2 = new DeadLock();
        d2.setTag("b");
         
        Thread t1 = new Thread(d1, "t1");
        Thread t2 = new Thread(d2, "t2");
         
        t1.start();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        t2.start();
    }   
}