Java使用jstack排查死锁(面试考点)

jps -l

jstack <pid> > thread_dump.txt

jstack 12345 > thread_dump.txt

jstack -l 12345 > thread_dump.txt

Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x00007f8b5c00a5a8 (object 0x00000000d5f6e3a0, a java.lang.Object),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x00007f8b5c00b0b0 (object 0x00000000d5f6e3b0, a java.lang.Object),
  which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
        at com.example.DeadlockExample.method2(DeadlockExample.java:25)
        - waiting to lock <0x00000000d5f6e3a0> (a java.lang.Object)
        - locked <0x00000000d5f6e3b0> (a java.lang.Object)
        at com.example.DeadlockExample.run(DeadlockExample.java:15)
"Thread-0":
        at com.example.DeadlockExample.method1(DeadlockExample.java:18)
        - waiting to lock <0x00000000d5f6e3b0> (a java.lang.Object)
        - locked <0x00000000d5f6e3a0> (a java.lang.Object)
        at com.example.DeadlockExample.run(DeadlockExample.java:10)

public class DeadlockExample implements Runnable {
    private final Object lock1 = new Object();
    private final Object lock2 = new Object();
    @Override
    public void run() {
        if (Thread.currentThread().getName().equals("Thread-0")) {
            method1();
        } else {
            method2();
        }
    }
    private void method1() {
        synchronized (lock1) {
            System.out.println("Thread-0 持有 lock1");
            try { Thread.sleep(100); } catch (InterruptedException e) {}
            synchronized (lock2) {
                System.out.println("Thread-0 持有 lock2");
            }
        }
    }
    private void method2() {
        synchronized (lock2) {
            System.out.println("Thread-1 持有 lock2");
            try { Thread.sleep(100); } catch (InterruptedException e) {}
            synchronized (lock1) {
                System.out.println("Thread-1 持有 lock1");
            }
        }
    }
    public static void main(String[] args) {
        DeadlockExample example = new DeadlockExample();
        Thread t1 = new Thread(example, "Thread-0");
        Thread t2 = new Thread(example, "Thread-1");
        t1.start();
        t2.start();
    }
}

# 1. 找到 PID
jps -l
# 2. 生成快照
jstack -l 12345 > deadlock.txt
# 3. 查看死锁摘要
grep -A 20 "Found one Java-level deadlock" deadlock.txt