Arthas-thread命令定位线程死锁

模拟死锁的场景

public class Deadlock {
    private static Object obj1 = new Object();
    private static Object obj2 = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            System.out.println("线程1执行");
            synchronized (obj1) {
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (obj2) {
                }
            }
        }, "t1").start();
        new Thread(() -> {
            System.out.println("线程2执行");
            synchronized (obj2) {
                synchronized (obj1) {
                }
            }
        }, "t2").start();
        System.out.println("执行完毕");
    }
}

通过thread命令定位

1，直接使用”thread“命令，输出线程统计信息。其中：BLOCKED 表示目前阻塞的线程数。

[[email protected]]$ thread

Threads Total: 26, NEW: 0, RUNNABLE: 8, BLOCKED: 2, WAITING: 4, TIMED_WAITING: 2, TERMINATED: 0, Internal threads: 10
ID   NAME                          GROUP          PRIORITY  STATE    %CPU      DELTA_TIM TIME      INTERRUPT DAEMON
2    Reference Handler             system         10        WAITING  0.0       0.000     0:0.000   false     true
3    Finalizer                     system         8         WAITING  0.0       0.000     0:0.000   false     true
4    Signal Dispatcher             system         9         RUNNABLE 0.0       0.000     0:0.000   false     true
5    Attach Listener               system         5         RUNNABLE 0.0       0.000     0:0.031   false     true
14   arthas-timer                  system         5         WAITING  0.0       0.000     0:0.015   false     true
17   arthas-NettyHttpTelnetBootstr system         5         RUNNABLE 0.0       0.000     0:0.015   false     true
18   arthas-NettyWebsocketTtyBoots system         5         RUNNABLE 0.0       0.000     0:0.015   false     true
19   arthas-NettyWebsocketTtyBoots system         5         RUNNABLE 0.0       0.000     0:0.015   false     true
20   arthas-shell-server           system         5         TIMED_WA 0.0       0.000     0:0.000   false     true
21   arthas-session-manager        system         5         TIMED_WA 0.0       0.000     0:0.000   false     true
22   arthas-UserStat               system         5         WAITING  0.0       0.000     0:0.000   false     true
24   arthas-NettyHttpTelnetBootstr system         5         RUNNABLE 0.0       0.000     0:0.109   false     true
25   arthas-command-execute        system         5         RUNNABLE 0.0       0.000     0:0.015   false     true
10   t1                            main           5         BLOCKED  0.0       0.000     0:0.000   false     false
11   t2                            main           5         BLOCKED  0.0       0.000     0:0.000   false     false
12   DestroyJavaVM                 main           5         RUNNABLE 0.0       0.000     0:0.156   false     false

2，执行“thread -b”命令，找出当前阻塞其他线程的线程，即造成死锁的罪魁祸首

[[email protected]]$ thread -b

"t1" Id=10 BLOCKED on [email protected] owned by "t2" Id=11
    at test.Deadlock.lambda$main$0(Deadlock.java:24)
    -  blocked on [email protected]
    -  locked [email protected] <---- but blocks 1 other threads!
    at test.Deadlock$$Lambda$1/250421012.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)

注：上面这个命令直接输出了 造成死锁的线程ID，和具体的代码位置，以及当前线程一共阻塞的线程数量：“<—- but blocks 1 other threads!“。

3，其他线程命令：

thread –all, 显示所有的线程；
thread id, 显示指定线程的运行堆栈；
thread –state：查看指定状态的线程，如：thread –state BLOCKED；
thread -n 3：展示当前最忙的前N个线程并打印堆栈；