jstack配合top命令分析CPU飙高、程序死锁问题

时间：2021-10-20 00:44:26

jstack：Java堆栈跟踪工具

jstack（Stack Trace for Java)命令用于生成虚拟机当前时刻的线程快照（一般称为threaddump或者javacore文件）。线程快照就是当前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都是导致线程长时间停顿的常见原因。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。jstack的官方文档地址为：https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstack.html。

jstack命令格式：jstack [option] vmid

jstack的主要option选项如下：

  • -F：当正常输出的请求不被响应时，强制输出线程堆栈。
  • -l：除堆栈外，显示关于锁的附加信息。
  • -m：除打印java线程堆栈外，还会输出native方法线程堆栈。

Java线程状态转化

官网线程状态介绍：https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr034.html，如下所示

  • NEW：创建了线程但是还没有调用start方法
  • RUNABLE：线程正在JVM中执行，有可能在等待CPU时间片轮转
  • TIMED_WAITING：线程等待指定的时间，一般则是处于sleep方法，wait方法，join等操作，正在等待时间
  • WAITING：线程无限期的等待，一般是wait，join等方法没有指定时间
  • BLOCKED：线程等待获取监视器锁而处于阻塞状态
  • TERMINATED：线程退出

关于线程各个状态的转化，从网上找了一张图，画的挺详细的。

jstack配合top命令分析CPU飙高、程序死锁问题

 jstack配合top命令分析CPU飙高问题

一般分析CPU飙高的步骤如下：

  • 先用top 命令在机器上分析出当前占用cpu的进程，
  • 通过top -H -p <pid>  查看进程内各个线程的资源占用
  • top -H -p <pid>命令输出的是这些线程的pid，然后通过jstack命令导出线程dump信息。把线程pid（对应线程dump内容中的nid，nid是16进制表示的）转换成十六进制，然后在线程dump文件中搜索即可找到对应的线程。

创建一个springboot工程，controller程序如下，然后通过package -Dmaven.test.skip=true打包之后放到Linux上运行：

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package com.wkp.jvm.chapter2;
 
import java.util.List;
 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class CpuController {
    
    Logger log=LoggerFactory.getLogger(CpuController.class);
    
    /**
     * 演示死循环
     */
    @RequestMapping("/loop")
    public List<Long> loop(){
        log.info("演示死循环============");
        while(true){
            
        }
    }
    
    private Object lock1 = new Object();
    private Object lock2 = new Object();
    /**
     * 演示死锁
     */
    @RequestMapping("/deadlock")
    public String deadlock() {
        log.info("演示死锁============");
        new Thread(()->{
            synchronized(lock1) {
                try {Thread.sleep(1000);} catch(Exception e) {}
                synchronized(lock2){
                    System.out.println("Thread 1 over");
                }
            }
        }).start();
        new Thread(()->{
            synchronized(lock2) {
                try {Thread.sleep(1000);} catch(Exception e) {}
                synchronized(lock1){
                    System.out.println("Thread 2 over");
                }
            }
        }).start();
        return "deadlock";
    }
}

通过http://ip:port/loop访问触发程序死循环，多访问几次之后，在Linux上通过top命令可以看到我们的Java应用程序CPU占用越来越高，系统负载也逐渐升高。

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[root@wkp ~]# top
top - 18:13:31 up 321 days,  3:37,  4 users,  load average: 13.14, 9.15, 4.72
Tasks: 128 total,   1 running, 108 sleeping,  19 stopped,   0 zombie
Cpu(s): 99.8%us,  0.2%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8193352k total,  7702892k used,   490460k free,     9204k buffers
Swap:        0k total,        0k used,        0k free,    75428k cached
 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                                                        
26295 root      20   0 4524m 378m  13m S 184.8  4.7  13:51.51 java

通过top命令，我们观察到java进程26295占用CPU很高，系统负载也越来越高.然后我们通过top -Hp 26295查看进程的线程占用情况。

top -Hp pid 可以查看某个进程的线程信息，其中-H 显示线程信息，-p指定pid

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[root@wkp~]# top -Hp 26295
top - 18:16:39 up 321 days,  3:40,  4 users,  load average: 13.24, 11.14, 6.33
Tasks:  31 total,  12 running,  19 sleeping,   0 stopped,   0 zombie
Cpu(s): 99.8%us,  0.2%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8193352k total,  7673852k used,   519500k free,     9752k buffers
Swap:        0k total,        0k used,        0k free,    75508k cached
 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                                                        
26379 root      20   0 4524m 378m  13m R 15.6  4.7   2:36.42 java                                                                                                                                                                                                            
26384 root      20   0 4524m 378m  13m R 15.6  4.7   1:41.46 java                                                                                                                                                                                                            
26388 root      20   0 4524m 378m  13m R 15.6  4.7   1:10.34 java                                                                                                                                                                                                            
 5673 root      20   0 4524m 378m  13m R 15.6  4.7   1:07.09 java                                                                                                                                                                                                            
26386 root      20   0 4524m 378m  13m R 15.3  4.7   1:17.68 java                                                                                                                                                                                                            
26380 root      20   0 4524m 378m  13m R 15.0  4.7   2:18.31 java                                                                                                                                                                                                            
26381 root      20   0 4524m 378m  13m R 15.0  4.7   2:05.06 java                                                                                                                                                                                                            
26382 root      20   0 4524m 378m  13m R 15.0  4.7   1:45.69 java                                                                                                                                                                                                            
26385 root      20   0 4524m 378m  13m R 15.0  4.7   1:20.29 java                                                                                                                                                                                                            
26387 root      20   0 4524m 378m  13m R 15.0  4.7   1:13.59 java                                                                                                                                                                                                            
 5801 root      20   0 4524m 378m  13m R 15.0  4.7   0:51.41 java                                                                                                                                                                                                            
26383 root      20   0 4524m 378m  13m R 14.6  4.7   1:55.11 java                                                                                                                                                                                                            
26295 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26305 root      20   0 4524m 378m  13m S  0.0  4.7   0:02.63 java                                                                                                                                                                                                            
26306 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.21 java                                                                                                                                                                                                            
26307 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.20 java                                                                                                                                                                                                            
26311 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.36 java                                                                                                                                                                                                            
26312 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26314 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.01 java                                                                                                                                                                                                            
26327 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26328 root      20   0 4524m 378m  13m S  0.0  4.7   0:03.67 java                                                                                                                                                                                                            
26329 root      20   0 4524m 378m  13m S  0.0  4.7   0:01.33 java                                                                                                                                                                                                            
26330 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26331 root      20   0 4524m 378m  13m S  0.0  4.7   0:01.79 java                                                                                                                                                                                                            
26376 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.06 java                                                                                                                                                                                                            
26377 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26378 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.13 java                                                                                                                                                                                                            
26389 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.13 java                                                                                                                                                                                                            
26390 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.11 java                                                                                                                                                                                                            
26391 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.00 java                                                                                                                                                                                                            
26392 root      20   0 4524m 378m  13m S  0.0  4.7   0:00.16 java

然后我们执行 jstack  26295 > threadstack.txt 命令，将线程dump信息输出到txt文件中，然后下载下来。因为jstack打印出的线程堆栈中线程号是16进制的，所以我们从上面top -Hp命令打印出的线程中选取第一个26379，通过 printf "%x\n" 26379转为16进制得到670b。

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[wkp@wkp4 Desktop]$ printf "%x\n" 26379
670b

 然后我们通过16进制的线程号670b，在threadstack.txt文件中搜索，可以搜到对应的线程（内容太多了，只贴了一小部分）：可以看到 at com.wkp.jvm.chapter2.CpuController.loop(CpuController.java:21)，第21行就对应我们的while（true）死循环，这样就找到了CPU飙高的原因了。

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2019-09-24 18:17:55
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.162-b12 mixed mode):
//=========省略===============================================
"http-nio-9999-exec-1" #16 daemon prio=5 os_prio=0 tid=0x00007fa06943c800 nid=0x670b runnable [0x00007fa01b3e9000]
   java.lang.Thread.State: RUNNABLE
    at com.wkp.jvm.chapter2.CpuController.loop(CpuController.java:21)
    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)
//=========省略===============================================
    
"C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007fa06813e000 nid=0x66d9 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE
 
"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007fa06813b000 nid=0x66d8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE
   
"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007fa068106800 nid=0x66ca in Object.wait() [0x00007fa054267000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x0000000082ebc820> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
    - locked <0x0000000082ebc820> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:212)
    
"VM Thread" os_prio=0 tid=0x00007fa0680fa000 nid=0x66c7 runnable
 
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007fa06801e000 nid=0x66c2 runnable
 
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007fa068020000 nid=0x66c3 runnable
 
"VM Periodic Task Thread" os_prio=0 tid=0x00007fa068146000 nid=0x66db waiting on condition
 
JNI global references: 913

下面我们对线程dump日志的格式做个介绍，以 "http-nio-9999-exec-1" #16 daemon prio=5 os_prio=0 tid=0x00007fa06943c800 nid=0x670b runnable [0x00007fa01b3e9000]为例：

  • http-nio-9999-exec-1：线程名称
  • daemon线程类型：线程分为守护线程 (daemon) 和非守护线程 (non-daemon) 两种，通常都是守护线程
  • prio=5：线程优先级：默认为5，数字越大优先级越高
  • tid=0x00007fa06943c800JVM线程的id：JVM内部线程的唯一标识，通过 java.lang.Thread.getId()获取，通常用自增的方式实现；
  • nid=0x670b系统线程id：对应的系统线程id（Native Thread ID)，可以通过 top -Hp 命令进行查看，线程id是十六进制的形式
  • runnable：系统线程的状态 
  • [0x00007fa01b3e9000]起始栈地址：线程堆栈调用的起始内存地址

其他的线程名含义：

  • "C1 CompilerThread1"和"C1 CompilerThread0"是Java的编译线程
  • "Finalizer"是垃圾回收时，被标记的对象被放到F-Queue队列中，Finalizer线程取出队列中的对象进行处理
  • "GC task thread#0 (ParallelGC)" 和"GC task thread#1 (ParallelGC)" 是ParallelGC垃圾收集器的工作线程 

jstack配合top命令查找死锁

我们演示一下死锁问题的查找：同样是启动上面的示例springboot程序，然后访问 http://ip:port/deadlock触发程序死锁。然后通过jstack导出线程dump文件，在文件末尾可以看到如下内容：

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Found one Java-level deadlock:
=============================
"Thread-5":
  waiting to lock monitor 0x00007fc978003778 (object 0x00000000833d0c20, a java.lang.Object),
  which is held by "Thread-4"
"Thread-4":
  waiting to lock monitor 0x00007fc978003568 (object 0x00000000833d0c30, a java.lang.Object),
  which is held by "Thread-5"
 
Java stack information for the threads listed above:
===================================================
"Thread-5":
    at com.wkp.jvm.chapter2.CpuController.lambda$deadlock$1(CpuController.java:46)
    - waiting to lock <0x00000000833d0c20> (a java.lang.Object)
    - locked <0x00000000833d0c30> (a java.lang.Object)
    at com.wkp.jvm.chapter2.CpuController$$Lambda$343/408916933.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)
"Thread-4":
    at com.wkp.jvm.chapter2.CpuController.lambda$deadlock$0(CpuController.java:38)
    - waiting to lock <0x00000000833d0c30> (a java.lang.Object)
    - locked <0x00000000833d0c20> (a java.lang.Object)
    at com.wkp.jvm.chapter2.CpuController$$Lambda$342/620117450.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)
 
Found 1 deadlock.

可以看到线程dump中已经把出现死锁的线程打印出来了，Thread-4和Thread-5互相等待对方持有的锁。

其实关于线程的dump和死锁检查等，JDK提供的有可视化的工具，比如 jconsole和jvisualvm 也是可以做到的。

另外，我们还可以通过如下 Thread.getAllStackTraces() 打印线程信息

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@RequestMapping("/getAllThreadStack")
public void getAllThreadStack() {
    for (Entry<Thread, StackTraceElement[]> stackTrace : Thread
            .getAllStackTraces().entrySet()) {
        Thread thread = (Thread) stackTrace.getKey();
        StackTraceElement[] stack = (StackTraceElement[]) stackTrace
                .getValue();
        if (thread.equals(Thread.currentThread())) {
            continue;
        }
        System.out.println("线程：" + thread.getName());
        for (StackTraceElement stackTraceElement : stack) {
            System.out.println(stackTraceElement);
        }
    }
}

到此这篇关于jstack配合top命令分析CPU飙高、程序死锁问题的文章就介绍到这了,更多相关Java 程序死锁内容请搜索服务器之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持服务器之家！

原文链接：https://blog.csdn.net/u012988901/article/details/101039614

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