jstack命令详解

jstack命令可以用来查看运行的Java进程下，多线程的运行情况，语句如“[root@admin ~]# jstack 43616 Full thread dump Java HotSpot(TM) 64-Bit Server...”。

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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：

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 ~]# jps 42576 Jps 43616 DeadLock

[root@admin ~]# jstack 43616 Full 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 condition JNI global references: 105 Found 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

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