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Demonstration and troubleshooting of deadlock phenomenon

Run the following code in the IDE tool and find that it does not exit. Click the DeadLockDemoclass, right-click, open in Terminaland open the console.

package thread;

import java.util.concurrent.TimeUnit;

public class DeadLockDemo {
    
    
    public static void main(String[] args) {
    
    
        String lockA = "lockA";
        String lockB = "lockB";
        new Thread(new HoldLockThread(lockA, lockB), "ThreadA").start();
        new Thread(new HoldLockThread(lockB, lockA), "ThreadB").start();
    }
}

class HoldLockThread implements Runnable {
    
    
    private String lockA;
    private String lockB;

    public HoldLockThread(String lockA, String lockB) {
    
    
        this.lockA = lockA;
        this.lockB = lockB;
    }

    @Override
    public void run() {
    
    
        synchronized (lockA) {
    
    
            System.out.println(Thread.currentThread().getName() + "\t自己持有：" + lockA + "\t尝试获取：" + lockB);
            try {
    
    
                TimeUnit.SECONDS.sleep(2);
            } catch (Exception e) {
    
    
                e.printStackTrace();
            }
            synchronized (lockB) {
    
    
                System.out.println(Thread.currentThread().getName() + "\t自己持有：" + lockB + "\t尝试获取：" + lockA);
            }
        }
    }
}

Input box jps -l, view thread list, input jstack 线程ID.

jps -l

jstack 7104

At this time, a deadlock was discovered. Found 1 deadlock..