JVM调优—jstack用法

jstack可用于生成JVM当前的线程快照，可快速定位线程间死锁、死循环或者线程长时间等待停顿的原因。

jstack命令格式

jstack [option] LVMID 

option参数

-F : 当正常输出请求不被响应时，强制输出线程堆栈

-l : 除堆栈外，显示关于锁的附加信息

-m : 如果调用到本地方法的话，可以显示C/C++的堆栈

Linux下jstack用法

(一)找到进程号：90464

使用命令ps -ef | grep tomcat

(二)找出该进程的占用CPU的线程情况

可以看出占用CPU最高的线程号是90485

使用命令：top -Hp 90464

(三)将90485转换为16进制:16175

使用命令printf "%x\n" 90485

(四)使用jstack命令查看该线程的堆栈信息

使用命令：jstack 90464 | grep 16175

 

(五)Jstack检查死锁的例子

首先看一个java实例: 

package com.lixin.learning.thread;   publicclassTestDeadThreadimplementsRunnable{        publicstaticObjecto1=newObject();      publicstaticObjecto2=newObject();      privatebooleanflag;        publicTestDeadThread(booleanflag){          this.flag=flag;      }        @Override      publicvoidrun(){          StringthreadName=Thread.currentThread().getName();          if(flag){               while(true){                    synchronized(o1){                        try{                             Thread.sleep(1000);                        }catch(InterruptedExceptione){                             e.printStackTrace();                        }                        System.out.println(threadName+"get o1 lock");                        synchronized(o2){                             System.out.println(threadName+"get o2 lock");                        }                    }               }          }else{               while(true){                    synchronized(o2){                        try{                             Thread.sleep(1000);                        }catch(InterruptedExceptione){                             e.printStackTrace();                        }                        System.out.println(threadName+"get o2 lock");                        synchronized(o1){                             System.out.println(threadName+"get o1 lock");                        }                    }               }          }        }        publicstaticvoidmain(String[]args){          TestDeadThreadthreada=newTestDeadThread(true);          TestDeadThreadthreadb=newTestDeadThread(false);            Threada=newThread(threada);          Threadb=newThread(threadb);            a.start();          b.start();      }   }

 输出结果：

Thread-0get o1 lock Thread-1get o2 lock

1：线程1首先获取对象1的锁，然后睡眠1秒钟

2：线程2获取对象2的锁，也睡眠1秒钟

3：线程1睡眠时间到，想要获取对象2的锁，但是对象2的锁已经被线程2持有，则等待对象2解锁。

4：线程2睡眠时间，想要获取对象1的锁，但是对象1的锁已经被线程1持有，则等待对象1解锁。

这样线程1和线程2相互等待，进入死锁状态。 

 

先通过jps（JVM Process Status）获取进程号

C:\Program  Files\Java\jdk1.8.0_77\bin>jps -l 10736 7808  com.lixin.learning.thread.TestDeadThread 5960 sun.tools.jps.Jps

使用jstack生成java虚拟机当前时刻的线程快照

C:\Program  Files\Java\jdk1.8.0_77\bin>jstack -l 7808 > e:/a.jstack

2017-03-14 10:12:19 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.77-b03  mixed mode):   "DestroyJavaVM" #12 prio=5 os_prio=0  tid=0x00000000024ce800 nid=0x1ac8 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "Thread-1" #11 prio=5 os_prio=0  tid=0x0000000058b4b000 nid=0x26c8 waiting for monitor entry  [0x0000000059bce000] java.lang.Thread.State: BLOCKED (on object monitor) at  com.lixin.learning.thread.TestDeadThread.run(TestDeadThread.java:39) - waiting to lock <0x00000000d5cf2640> (a  java.lang.Object) - locked <0x00000000d5cf2650> (a java.lang.Object) at java.lang.Thread.run(Unknown Source)   Locked ownable synchronizers: - None   "Thread-0" #10 prio=5 os_prio=0  tid=0x0000000058b48800 nid=0x2018 waiting for monitor entry  [0x00000000599ce000] java.lang.Thread.State: BLOCKED (on object monitor) at  com.lixin.learning.thread.TestDeadThread.run(TestDeadThread.java:25) - waiting to lock <0x00000000d5cf2650> (a  java.lang.Object) - locked <0x00000000d5cf2640> (a java.lang.Object) at java.lang.Thread.run(Unknown Source)   Locked ownable synchronizers: - None   "Service Thread" #9 daemon prio=9 os_prio=0  tid=0x0000000058ae7800 nid=0x310c runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "C1 CompilerThread2" #8 daemon prio=9 os_prio=2  tid=0x0000000058a75000 nid=0x1cb0 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "C2 CompilerThread1" #7 daemon prio=9 os_prio=2  tid=0x0000000058a6c000 nid=0x2388 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "C2 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x0000000058a6b000  nid=0xb1c waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "Attach Listener" #5 daemon prio=5 os_prio=2  tid=0x0000000058a6a000 nid=0x30fc waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "Signal Dispatcher" #4 daemon prio=9 os_prio=2  tid=0x0000000058a67800 nid=0x2e6c runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE   Locked ownable synchronizers: - None   "Finalizer" #3 daemon prio=8 os_prio=1  tid=0x000000005758b800 nid=0x309c in Object.wait() [0x0000000058a4f000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d5c08ee0> (a  java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(Unknown Source) - locked <0x00000000d5c08ee0> (a  java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(Unknown Source) at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)   Locked ownable synchronizers: - None   "Reference Handler" #2 daemon prio=10 os_prio=2  tid=0x0000000057544800 nid=0x2708 in Object.wait() [0x00000000588cf000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d5c06b50> (a  java.lang.ref.Reference$Lock) at java.lang.Object.wait(Unknown Source) at java.lang.ref.Reference.tryHandlePending(Unknown Source) - locked <0x00000000d5c06b50> (a  java.lang.ref.Reference$Lock) at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)   Locked ownable synchronizers: - None   "VM Thread" os_prio=2 tid=0x000000005753c800  nid=0x1ad4 runnable   "GC task thread#0 (ParallelGC)" os_prio=0  tid=0x000000000263f000 nid=0x28bc runnable   "GC task thread#1 (ParallelGC)" os_prio=0  tid=0x0000000002640800 nid=0x2b04 runnable   "GC task thread#2 (ParallelGC)" os_prio=0  tid=0x0000000002642000 nid=0x22a0 runnable   "GC task thread#3 (ParallelGC)" os_prio=0  tid=0x0000000002645800 nid=0x215c runnable   "VM Periodic Task Thread" os_prio=2  tid=0x0000000058b26800 nid=0x2e7c waiting on condition   JNI global references: 6     Found one Java-level deadlock: ============================= "Thread-1": waiting to lock monitor 0x000000005754b148 (object  0x00000000d5cf2640, a java.lang.Object), which is held by "Thread-0" "Thread-0": waiting to lock monitor 0x0000000057548cd8 (object  0x00000000d5cf2650, a java.lang.Object), which is held by "Thread-1"   Java stack information for the threads listed above: =================================================== "Thread-1": at  com.lixin.learning.thread.TestDeadThread.run(TestDeadThread.java:39) - waiting to lock <0x00000000d5cf2640> (a  java.lang.Object) - locked <0x00000000d5cf2650> (a java.lang.Object) at java.lang.Thread.run(Unknown Source) "Thread-0": at  com.lixin.learning.thread.TestDeadThread.run(TestDeadThread.java:25) - waiting to lock <0x00000000d5cf2650> (a java.lang.Object) - locked <0x00000000d5cf2640> (a java.lang.Object) at java.lang.Thread.run(Unknown Source)   Found 1 deadlock.

 可以看到jstack检查到了一个线程间死锁。