概述

使用jstack命令，排查线程死锁问题。

jstack是什么？

jstack是java虚拟机自带的一种堆栈跟踪工具。jstack用于打印出给定的java进程ID或core file或远程调试服务的Java堆栈信息

jstack有什么作用

jstack主要用于生成java虚拟机当前时刻的线程快照。线程快照是当前java虚拟机内每一条线程正在执行的方法堆栈的集合，生成线程快照的主要目的是定位线程出现长时间停顿的原因，如线程间死锁、死循环、请求外部资源导致的长时间等待等。线程出现停顿的时候通过jstack来查看各个线程的调用堆栈，就可以知道没有响应的线程到底在后台做什么事情，或者等待什么资源。如果现在运行的java程序呈现hung的状态，jstack是非常有用的。

如何使用？

使用jstack -help查看官方文档

Usage:
    jstack [-l] <pid>
        (to connect to running process)
    jstack -F [-m] [-l] <pid>
        (to connect to a hung process)
    jstack [-m] [-l] <executable> <core>
        (to connect to a core file)
    jstack [-m] [-l] [server_id@]<remote server IP or hostname>
        (to connect to a remote debug server)

Options:
    -F  to force a thread dump. Use when jstack <pid> does not respond (process is hung)
    -m  to print both java and native frames (mixed mode)
    -l  long listing. Prints additional information about locks
    -h or -help to print this help message

参数解释

-F：当正常输出的请求不被响应时（jstack <pid>无响应），强制输出线程堆栈。

-m：如果调用到本地方法的话，可以显示C/C++的堆栈 

-l：除堆栈外，会打印出额外的锁信息，在发生死锁时可以用jstack -l pid来观察锁持有情况

实战使用

1. 模拟死锁情形

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

/**
 * <pre>
 * 	程序目的：模拟线程死锁
 * </pre>
 * created at 2020-06-21 17:54
 * @author lerry
 */
public class DeathLockDemo {
	public static void main(String[] args) {
		deathLock();
	}

	/**
	 * 一个模拟死锁的方法。
	 */
	public static void deathLock() {
		ReentrantLock lock1 = new ReentrantLock();
		ReentrantLock lock2 = new ReentrantLock();

		Thread t1 = new Thread(() -> {
			try {
				lock1.lock();
				TimeUnit.SECONDS.sleep(1);
				lock2.lock();
			}
			catch (InterruptedException e) {
				e.printStackTrace();
			}
		});
		Thread t2 = new Thread(() -> {
			try {
				lock2.lock();
				TimeUnit.SECONDS.sleep(1);
				lock1.lock();
			}
			catch (InterruptedException e) {
				e.printStackTrace();
			}
		});
		t1.setName("mythread1");
		t2.setName("mythread2");

		System.out.println("启动两个线程");
		t1.start();
		t2.start();
	}
}

2. 查找该程序的pid

1）方法1 使用ps命令

ps -ef | grep 'DeathLockDemo'

输出结果为：

图：DeathLockDemo的进程信息
可以查到，该程序的进程编号为15019
2)方法2 使用jps命令

jps

输出结果为：

➜  ~ jps
14736 KotlinCompileDaemon
10720 Launcher
10721 Bootstrap
15462 Jps
3608 
15017 Launcher
15019 DeathLockDemo
13471

同样可以查看到该程序的进程编号为15019

3. 使用jstack

jstack -l 15019

输出结果如下：

2020-06-21 18:25:09
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.251-b08 mixed mode):

"Attach Listener" #16 daemon prio=9 os_prio=31 tid=0x00007faae8835800 nid=0x5c03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"DestroyJavaVM" #15 prio=5 os_prio=31 tid=0x00007faae684e800 nid=0x1603 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"mythread2" #14 prio=5 os_prio=31 tid=0x00007faae684e000 nid=0xa803 waiting on condition [0x000070001022c000]
   java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076aea4848> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at com.hua.jvm.DeathLockDemo.lambda$deathLock$1(DeathLockDemo.java:39)
	at com.hua.jvm.DeathLockDemo$$Lambda$2/240650537.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
	- <0x000000076aea4878> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

"mythread1" #13 prio=5 os_prio=31 tid=0x00007faae684d000 nid=0xa903 waiting on condition [0x0000700010129000]
   java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076aea4878> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at com.hua.jvm.DeathLockDemo.lambda$deathLock$0(DeathLockDemo.java:29)
	at com.hua.jvm.DeathLockDemo$$Lambda$1/1809787067.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
	- <0x000000076aea4848> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

"Service Thread" #12 daemon prio=9 os_prio=31 tid=0x00007faae580c800 nid=0x5703 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C1 CompilerThread3" #11 daemon prio=9 os_prio=31 tid=0x00007faae802b800 nid=0x5503 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C2 CompilerThread2" #10 daemon prio=9 os_prio=31 tid=0x00007faae580b800 nid=0x3f03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C2 CompilerThread1" #9 daemon prio=9 os_prio=31 tid=0x00007faae800f800 nid=0x4003 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C2 CompilerThread0" #8 daemon prio=9 os_prio=31 tid=0x00007faae8828800 nid=0x4103 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"JDWP Command Reader" #7 daemon prio=10 os_prio=31 tid=0x00007faae802b000 nid=0x4203 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"JDWP Event Helper Thread" #6 daemon prio=10 os_prio=31 tid=0x00007faae6010800 nid=0x4303 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"JDWP Transport Listener: dt_socket" #5 daemon prio=10 os_prio=31 tid=0x00007faae8824800 nid=0x4507 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007faae6819800 nid=0x4607 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007faae6810800 nid=0x5003 in Object.wait() [0x000070000f608000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000076ab08ee0> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
	- locked <0x000000076ab08ee0> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
	at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

   Locked ownable synchronizers:
	- None

"Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007faae7815800 nid=0x5103 in Object.wait() [0x000070000f505000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000076ab06c00> (a java.lang.ref.Reference$Lock)
	at java.lang.Object.wait(Object.java:502)
	at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
	- locked <0x000000076ab06c00> (a java.lang.ref.Reference$Lock)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

   Locked ownable synchronizers:
	- None

"VM Thread" os_prio=31 tid=0x00007faae680e000 nid=0x5203 runnable 

"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007faae8803800 nid=0x1e07 runnable 

"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007faae9000000 nid=0x1f03 runnable 

"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007faae6804000 nid=0x2a03 runnable 

"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007faae780c800 nid=0x2c03 runnable 

"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007faae780d000 nid=0x2e03 runnable 

"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007faae780d800 nid=0x5403 runnable 

"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007faae780e800 nid=0x3003 runnable 

"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007faae780f000 nid=0x3203 runnable 

"VM Periodic Task Thread" os_prio=31 tid=0x00007faae7880800 nid=0x5903 waiting on condition 

JNI global references: 2537


Found one Java-level deadlock:
=============================
"mythread2":
  waiting for ownable synchronizer 0x000000076aea4848, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "mythread1"
"mythread1":
  waiting for ownable synchronizer 0x000000076aea4878, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "mythread2"

Java stack information for the threads listed above:
===================================================
"mythread2":
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076aea4848> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at com.hua.jvm.DeathLockDemo.lambda$deathLock$1(DeathLockDemo.java:39)
	at com.hua.jvm.DeathLockDemo$$Lambda$2/240650537.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)
"mythread1":
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076aea4878> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at com.hua.jvm.DeathLockDemo.lambda$deathLock$0(DeathLockDemo.java:29)
	at com.hua.jvm.DeathLockDemo$$Lambda$1/1809787067.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.

4. 结果分析

图：截取的部分jstack输出结果
根据输出，可以发现：
线程mythread2在等待正在由mythread1持有的锁0x000000076aea4848。
而线程mythread1同时又在等待正在由mythread2持有的锁0x000000076aea4878。造成了死锁问题。

jstack日志分析工具

可以把jstack输出到文本中，然后使用分析工具查看

~ jstack -l 15019 > ~/Temp/jstack15019.txt

图：fastthread.io的在线分析结果

参考

jvm 性能调优工具之 jstack - 简书

环境说明

java -version

java version "1.8.0_251"
Java(TM) SE Runtime Environment (build 1.8.0_251-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

OS：macOS High Sierra 10.13.4

使用jstack命令，排查线程死锁问题

概述

jstack是什么？

jstack有什么作用

如何使用？

参数解释

实战使用

1. 模拟死锁情形

2. 查找该程序的pid

3. 使用jstack

4. 结果分析

jstack日志分析工具

参考

环境说明

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