死锁实战（通过jps、jstack查看运行信息）

我们先来创造一个死锁的情况，代码如下：

public class DeadLockDemo {
          
   
    static Object resource1 = new Object();
    static Object resource2 = new Object();

    public static void main(String[] args) throws InterruptedException {
          
   
        new Thread(()->{
          
   
            synchronized (resource1) {
          
   
                try {
          
   
                    System.out.println(Thread.currentThread() + "get resource1");
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
          
   
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread() + "ready to get resource2");
                synchronized (resource2) {
          
   
                    System.out.println(Thread.currentThread() + "get resource2");
                }
            }
        }).start();
        new Thread(()->{
          
   
            synchronized (resource2) {
          
   
                System.out.println(Thread.currentThread() + "get resource2");
                try {
          
   
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
          
   
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread() + "ready to get resource1");
                synchronized (resource1) {
          
   
                    System.out.println(Thread.currentThread() + "get resource1");
                }
            }
        }).start();
        Thread.sleep(2000);
    }
}

当程序运行之后，程序会卡住，两个线程相互争夺资源造成死锁： 输出如下：

Thread[Thread-0,5,main]get resource1
Thread[Thread-1,5,main]get resource2
Thread[Thread-0,5,main]ready to get resource2
Thread[Thread-1,5,main]ready to get resource1

我们打开shell，键入

C:UsersAdministrator>jps
1096
12252 DeadLockDemo
13964 Jps
6604 Launcher

可以发现正在运行中的DeadLockDemo的pid为12252 我们继续键入：

C:UsersAdministrator>jstack 12252
2021-03-22 23:49:15
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.261-b12 mixed mode):

"DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x000001ffd2196000 nid=0x1bec waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Thread-1" #13 prio=5 os_prio=0 tid=0x000001ffd2197000 nid=0x2f30 waiting for monitor entry [0x000000b42ecff000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at DeadLockDemo.lambda$main$1(DeadLockDemo.java:34)
        - waiting to lock <0x000000076b6b07f0> (a java.lang.Object)
        - locked <0x000000076b6b0800> (a java.lang.Object)
        at DeadLockDemo$$Lambda$2/2093631819.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)

"Thread-0" #12 prio=5 os_prio=0 tid=0x000001ffd219c000 nid=0x92c waiting for monitor entry [0x000000b42ebff000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at DeadLockDemo.lambda$main$0(DeadLockDemo.java:20)
        - waiting to lock <0x000000076b6b0800> (a java.lang.Object)
        - locked <0x000000076b6b07f0> (a java.lang.Object)
        at DeadLockDemo$$Lambda$1/1023892928.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:748)