线程死锁

关于线程死锁

1. 死锁的基本概念
   多个线程彼此持有对方所需要的锁，而不释放自己已经持有的锁，导致这些线程永远都不能获取到锁而处于永远阻塞的状态

• 导致死锁的原因
  (1) 由于某些条件不成立，导致线程之间无法进行正常的同步操作
  (2) 环路等待，形成一个环路，比如a等待b，b等待c，c等待d，d等待a

• 死锁产生的必要条件
  (1) 只有两个或两个以上的线程才会产生死锁
  (2) 参与死锁的线程至少有2个已经占有共享资源

public class deadLock extends Thread {

    private String name;
    private long sleep = 3000;
    private long holdsLockSleep = 1000;

    public deadLock(String name){
        super(name);
        this.name = name;
    }

    private static Object lock1 = new Object();
    private static Object lock2 = new Object();


    public void deadLockRun(){
        try{
            if(this.name.equals("a线程")){
                synchronized (lock1){
                    System.out.println(Thread.currentThread().getName()+"获得lock1锁");
                    Thread.sleep(sleep);

                    this.haveLock(lock2);

                    //由于条件不满足，导致a线程永远阻塞，无法释放lock1锁
                    synchronized (lock2){
                        System.out.println(Thread.currentThread().getName()+"获得lock2锁");
                    }
                }
            }

            if(this.name.equals("b线程")){
                synchronized (lock2){
                    System.out.println(Thread.currentThread().getName()+"获得lock2锁");
                    Thread.sleep(sleep);

                    this.haveLock(lock1);

                    //由于条件不满足，导致b线程永远阻塞，无法释放lock2锁
                    synchronized (lock1){
                        System.out.println(Thread.currentThread().getName()+"获得lock1锁");
                    }
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    /**
     * 检测当前线程是否得到锁
     * @param lock
     */
    public void haveLock(Object lock){
        String threadName = Thread.currentThread().getName();
        try{
            while (!Thread.holdsLock(lock)){
                if(threadName.equals("a线程")){
                    System.out.println("是否获得lock2锁:"+Thread.holdsLock(lock2));
                }

                if(threadName.equals("b线程")){
                    System.out.println("是否获得lock1锁:"+Thread.holdsLock(lock1));
                }

                Thread.sleep(holdsLockSleep);
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }


    @Override
    public void run(){
        deadLockRun();
    }


    public static void main(String [] args){
        Thread t1 = new deadLock("a线程");
        Thread t2 = new deadLock("b线程");

        t1.start();
        t2.start();

    }
}

线程死锁

原文：https://www.cnblogs.com/xiaoquan66/p/15086045.html