使用jstack命令，排查线程死锁问题
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]
(to connect to running process)
jstack -F [-m] [-l]
(to connect to a hung process)
jstack [-m] [-l]
(to connect to a core file)
jstack [-m] [-l] [server_id@]
(to connect to a remote debug server)
Options:
-F to force a thread dump. Use when jstack 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 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;
/**
*
* 程序目的：模拟线程死锁
*
* 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