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jstack命令用于打印Java进程，core文件或者远程调试服务器的堆栈跟踪记录，它会打印类名，方法名，字节码索引（BCI），如果允许的话，还会打印出行号。

jstack主要用于生成线程快照，这样可以定位长时间停顿的原因，比如死锁或者死循环。

jstack的命令格式

jstack [ options ] pid

我在代码里特意写了个死循环，代码如下：

/** * Created by kevin on 11/4/16. */public class DeadLoop {
       public static void main(String[] args){        while (true);    }}

跑起来，用jps查看一下它的pid：

$ jps8544 AppMain8561 Launcher8587 Jps2815 Main

好，看到刚刚运行的代码的pid是8544，那就用jstack看一下8544的情况：

l$ jstack -l 85442016-11-04 16:16:51Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.101-b13 mixed mode):"Attach Listener" #10 daemon prio=9 os_prio=0 tid=0x00007fdd84001000 nid=0x21aa waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"Monitor Ctrl-Break" #9 daemon prio=5 os_prio=0 tid=0x00007fddbc13a800 nid=0x2170 runnable [0x00007fdda80ff000]   java.lang.Thread.State: RUNNABLE    at java.net.PlainSocketImpl.socketAccept(Native Method)    at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)    at java.net.ServerSocket.implAccept(ServerSocket.java:545)    at java.net.ServerSocket.accept(ServerSocket.java:513)    at com.intellij.rt.execution.application.AppMain$1.run(AppMain.java:90)    at java.lang.Thread.run(Thread.java:745)   Locked ownable synchronizers:    - None"Service Thread" #8 daemon prio=9 os_prio=0 tid=0x00007fddbc0c0800 nid=0x216e runnable [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"C1 CompilerThread2" #7 daemon prio=9 os_prio=0 tid=0x00007fddbc0bd000 nid=0x216d waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"C2 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007fddbc0bb800 nid=0x216c waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007fddbc0b8800 nid=0x216b waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007fddbc0b7000 nid=0x216a runnable [0x0000000000000000]   java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers:    - None"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007fddbc084000 nid=0x2169 in Object.wait() [0x00007fdda8a4d000]   java.lang.Thread.State: WAITING (on object monitor)    at java.lang.Object.wait(Native Method)    - waiting on <0x00000000ec188ee0> (a java.lang.ref.ReferenceQueue$Lock)    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)    - locked <0x00000000ec188ee0> (a java.lang.ref.ReferenceQueue$Lock)    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)   Locked ownable synchronizers:    - None"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007fddbc07f800 nid=0x2168 in Object.wait() [0x00007fdda8b4e000]   java.lang.Thread.State: WAITING (on object monitor)    at java.lang.Object.wait(Native Method)    - waiting on <0x00000000ec186b50> (a java.lang.ref.Reference$Lock)    at java.lang.Object.wait(Object.java:502)    at java.lang.ref.Reference.tryHandlePending(Reference.java:191)    - locked <0x00000000ec186b50> (a java.lang.ref.Reference$Lock)    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)   Locked ownable synchronizers:    - None"main" #1 prio=5 os_prio=0 tid=0x00007fddbc00a800 nid=0x2162 runnable [0x00007fddc30a1000]   java.lang.Thread.State: RUNNABLE    at DeadLoop.main(DeadLoop.java:6)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)   Locked ownable synchronizers:    - None"VM Thread" os_prio=0 tid=0x00007fddbc078000 nid=0x2167 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007fddbc01f800 nid=0x2163 runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007fddbc021000 nid=0x2164 runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00007fddbc023000 nid=0x2165 runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00007fddbc024800 nid=0x2166 runnable "VM Periodic Task Thread" os_prio=0 tid=0x00007fddbc0c3000 nid=0x216f waiting on condition JNI global references: 15

结果出来了，注意78,79行的输出：

java.lang.Thread.State: RUNNABLE    at DeadLoop.main(DeadLoop.java:6)

可以看到第6行这里有死循环，然后我们对照一下自己的源码，确实在第6行。

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