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...”。

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