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Java jstack 命令详解

Java 中 jstack 命令可以用来查看运行的 Java 进程下，多线程的运行情况，我们用一个死锁的例子来看：

比如下面这段死锁的代码：

点击下载“修复打印机驱动工具”；

public class DeadLock {    private static Object objA = new Object();    private static Object objB = new Object();    public static void main(String[] args) {        Thread thread1 = new Thread(new Thread1());        Thread thread2 = new Thread(new Thread2());        thread1.start();        thread2.start();    }    private static class Thread1 implements Runnable{        @Override        public void run() {            synchronized (objA) {                System.out.println("线程1得到A对象的锁");                try {                    Thread.sleep(3000);                } catch (InterruptedException e) {                    e.printStackTrace();                }                synchronized (objB) {                    System.out.println("线程1得到B对象的锁");                }            }        }    }    private static class Thread2 implements Runnable{        @Override        public void run() {            synchronized (objB) {                System.out.println("线程2得到B对象的锁");                try {                    Thread.sleep(3000);                } catch (InterruptedException e) {                    e.printStackTrace();                }                synchronized (objA) {                    System.out.println("线程2得到A对象的锁");                }            }        }       }}

当然，运行结果只能看到两个线程只拿到了一个锁，在一直等待对方的锁。

线程1得到A对象的锁线程2得到B对象的锁

我们可以使用 jps 来查看对应的 PID ，然后使用 jstack 来查看其线程情况：

[root@admin ~]# jps42576 Jps43616 DeadLock

[root@admin ~]# jstack 43616Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.45-b08 mixed mode):"DestroyJavaVM" prio=6 tid=0x00000000047c1000 nid=0x9878 waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"Thread-1" prio=6 tid=0x0000000010aa3000 nid=0xafa0 waiting for monitor entry [0x000000001105f000]   java.lang.Thread.State: BLOCKED (on object monitor)        at com.zaimeibian.Test$Thread2.run(Test.java:46)        - waiting to lock <0x00000007c099cc20> (a java.lang.Object)        - locked <0x00000007c099cc30> (a java.lang.Object)        at java.lang.Thread.run(Thread.java:744)"Thread-0" prio=6 tid=0x0000000010aa2800 nid=0xae74 waiting for monitor entry [0x0000000010f5f000]   java.lang.Thread.State: BLOCKED (on object monitor)        at com.zaimeibian.Test$Thread1.run(Test.java:27)        - waiting to lock <0x00000007c099cc30> (a java.lang.Object)        - locked <0x00000007c099cc20> (a java.lang.Object)        at java.lang.Thread.run(Thread.java:744)"Service Thread" daemon prio=6 tid=0x000000000f10a000 nid=0x9a8c runnable [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"C2 CompilerThread1" daemon prio=10 tid=0x000000000f109800 nid=0xaf28 waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"C2 CompilerThread0" daemon prio=10 tid=0x000000000f105800 nid=0x85dc waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"Attach Listener" daemon prio=10 tid=0x000000000f104800 nid=0xac04 waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"Signal Dispatcher" daemon prio=10 tid=0x000000000f102000 nid=0xa678 runnable [0x0000000000000000]   java.lang.Thread.State: RUNNABLE"Finalizer" daemon prio=8 tid=0x000000000f0bd000 nid=0xaed8 in Object.wait() [0x000000001045f000]   java.lang.Thread.State: WAITING (on object monitor)        at java.lang.Object.wait(Native Method)        - waiting on <0x00000007c0905568> (a java.lang.ref.ReferenceQueue$Lock)        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:135)        - locked <0x00000007c0905568> (a java.lang.ref.ReferenceQueue$Lock)        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:151)        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:189)"Reference Handler" daemon prio=10 tid=0x000000000f0b2000 nid=0xaedc in Object.wait() [0x000000001035f000]   java.lang.Thread.State: WAITING (on object monitor)        at java.lang.Object.wait(Native Method)        - waiting on <0x00000007c09050f0> (a java.lang.ref.Reference$Lock)        at java.lang.Object.wait(Object.java:503)        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)        - locked <0x00000007c09050f0> (a java.lang.ref.Reference$Lock)"VM Thread" prio=10 tid=0x000000000f0b0000 nid=0xaef0 runnable"GC task thread#0 (ParallelGC)" prio=6 tid=0x00000000047d6000 nid=0xacb0 runnable"GC task thread#1 (ParallelGC)" prio=6 tid=0x00000000047d8000 nid=0xaee0 runnable"GC task thread#2 (ParallelGC)" prio=6 tid=0x00000000047d9800 nid=0xaed4 runnable"GC task thread#3 (ParallelGC)" prio=6 tid=0x00000000047db000 nid=0xac54 runnable"VM Periodic Task Thread" prio=10 tid=0x000000000f132000 nid=0xaff0 waiting on conditionJNI global references: 105Found one Java-level deadlock:============================="Thread-1":  waiting to lock monitor 0x000000000f0ba488 (object 0x00000007c099cc20, a java.lang.Object),  which is held by "Thread-0""Thread-0":  waiting to lock monitor 0x000000000f0bcf28 (object 0x00000007c099cc30, a java.lang.Object),  which is held by "Thread-1"Java stack information for the threads listed above:==================================================="Thread-1":        at com.zaimeibian.Test$Thread2.run(Test.java:46)        - waiting to lock <0x00000007c099cc20> (a java.lang.Object)        - locked <0x00000007c099cc30> (a java.lang.Object)        at java.lang.Thread.run(Thread.java:744)"Thread-0":        at com.zaimeibian.Test$Thread1.run(Test.java:27)        - waiting to lock <0x00000007c099cc30> (a java.lang.Object)        - locked <0x00000007c099cc20> (a java.lang.Object)        at java.lang.Thread.run(Thread.java:744)Found 1 deadlock.

我们可以看到 jstack 打印出了线程的状态，而且发现一个死锁。

另外，线程状态有以下几种：

- RUNNABLE 线程运行中或 I/O 等待

- BLOCKED 线程在等待 monitor 锁( synchronized 关键字)

- TIMED_WAITING 线程在等待唤醒，但设置了时限

- WAITING 线程在无限等待唤醒