哪个Java线程占用了CPU？

Question

哪个Java线程占用了CPU？

Gen*_*rib 58 java cpu multithreading

假设你的Java程序占用了100%的CPU.它有50个线程.你需要找到哪个线程是有罪的.我还没有找到可以提供帮助的工具.目前我使用以下非常耗时的例行程序:

运行jstack <pid>,其中pid是Java进程的进程ID.找到它的简单方法是运行JDK中包含的另一个实用程序 - jps.最好将jstack的输出重定向到文件.
搜索"可运行"线程.跳过那些在套接字上等待的东西(由于某种原因它们仍然标记为可运行).
重复步骤1和2几次,看看是否可以找到一个模式.

或者,您可以附加到Eclipse中的Java进程并尝试逐个挂起线程,直到您遇到占用CPU的那个.在单CPU机器上,您可能需要首先降低Java进程的优先级才能移动.即便如此,由于超时,Eclipse通常无法附加到正在运行的进程.

我本来期望Sun的visualvm工具可以做到这一点.

有人知道更好的方法吗？

Answer 1

Vas*_*zos 77

确定哪个Java Thread消耗了生产服务器中的大多数CPU.

大多数(如果不是全部)生产系统执行任何重要操作将使用多于1个java线程.当一些事情变得疯狂并且你的cpu使用率达到100%时,很难确定导致这种情况的线程.或者我想.直到比我聪明的人向我展示如何做到这一点.在这里,我将告诉你如何做到这一点,你也可以用你的极客技巧让你的家人和朋友惊叹.

测试应用程序

为了测试这个,我们需要一个测试应用程序.所以我会给你一个.它由3个类组成:

一HeavyThread,做什么CPU密集型类(计算MD5哈希值)
一个LightThread不做cpu密集(计数和休眠)的类.
一个StartThreads类来启动1个cpu密集型和几个轻型线程.

以下是这些类的代码:

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;

/**
 * thread that does some heavy lifting
 *
 * @author srasul
 *
 */
public class HeavyThread implements Runnable {

        private long length;

        public HeavyThread(long length) {
                this.length = length;
                new Thread(this).start();
        }

        @Override
        public void run() {
                while (true) {
                        String data = "";

                        // make some stuff up
                        for (int i = 0; i < length; i++) {
                                data += UUID.randomUUID().toString();
                        }

                        MessageDigest digest;
                        try {
                                digest = MessageDigest.getInstance("MD5");
                        } catch (NoSuchAlgorithmException e) {
                                throw new RuntimeException(e);
                        }

                        // hash the data
                        digest.update(data.getBytes());
                }
        }
}


import java.util.Random;

/**
 * thread that does little work. just count & sleep
 *
 * @author srasul
 *
 */
public class LightThread implements Runnable {

        public LightThread() {
                new Thread(this).start();
        }

        @Override
        public void run() {
                Long l = 0l;
                while(true) {
                        l++;
                        try {
                                Thread.sleep(new Random().nextInt(10));
                        } catch (InterruptedException e) {
                                e.printStackTrace();
                        }
                        if(l == Long.MAX_VALUE) {
                                l = 0l;
                        }
                }
        }
}


/**
 * start it all
 *
 * @author srasul
 *
 */
public class StartThreads {

        public static void main(String[] args) {
                // lets start 1 heavy ...
                new HeavyThread(1000);

                // ... and 3 light threads
                new LightThread();
                new LightThread();
                new LightThread();
        }
}

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假设您从未见过这段代码,并且您拥有一个运行这些类并且正在消耗100%CPU的失控Java进程的PID.

首先让我们开始StartThreads上课.

$ ls
HeavyThread.java  LightThread.java  StartThreads.java
$ javac *
$ java StartThreads &

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在这个阶段,一个正在运行的Java进程应该占用100个cpu.在我的顶部,我看到: 最高输出的截图

在顶部按Shift-H打开线程.top的手册页说:

   -H : Threads toggle
        Starts top with the last remembered 'H' state reversed.  When
        this  toggle is On, all individual threads will be displayed.
        Otherwise, top displays a  summation  of  all  threads  in  a
        process.

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现在在我的顶部,线程显示器打开,我看到: 带有线程的顶部屏幕截图

我有一个javaPID过程28294.让我们使用以下方法获取此进程的堆栈转储jstack:

$ jstack 28924
2010-11-18 13:05:41
Full thread dump Java HotSpot(TM) 64-Bit Server VM (17.0-b16 mixed mode):

"Attach Listener" daemon prio=10 tid=0x0000000040ecb000 nid=0x7150 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DestroyJavaVM" prio=10 tid=0x00007f9a98027800 nid=0x70fd waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Thread-3" prio=10 tid=0x00007f9a98025800 nid=0x710d waiting on condition [0x00007f9a9d543000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at LightThread.run(LightThread.java:21)
    at java.lang.Thread.run(Thread.java:619)

"Thread-2" prio=10 tid=0x00007f9a98023800 nid=0x710c waiting on condition [0x00007f9a9d644000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at LightThread.run(LightThread.java:21)
    at java.lang.Thread.run(Thread.java:619)

"Thread-1" prio=10 tid=0x00007f9a98021800 nid=0x710b waiting on condition [0x00007f9a9d745000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at LightThread.run(LightThread.java:21)
    at java.lang.Thread.run(Thread.java:619)

"Thread-0" prio=10 tid=0x00007f9a98020000 nid=0x710a runnable [0x00007f9a9d846000]
   java.lang.Thread.State: RUNNABLE
    at sun.security.provider.DigestBase.engineReset(DigestBase.java:139)
    at sun.security.provider.DigestBase.engineUpdate(DigestBase.java:104)
    at java.security.MessageDigest$Delegate.engineUpdate(MessageDigest.java:538)
    at java.security.MessageDigest.update(MessageDigest.java:293)
    at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:197)
    - locked <0x00007f9aa457e400> (a sun.security.provider.SecureRandom)
    at sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:257)
    - locked <0x00007f9aa457e708> (a java.lang.Object)
    at sun.security.provider.NativePRNG$RandomIO.access$200(NativePRNG.java:108)
    at sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:97)
    at java.security.SecureRandom.nextBytes(SecureRandom.java:433)
    - locked <0x00007f9aa4582fc8> (a java.security.SecureRandom)
    at java.util.UUID.randomUUID(UUID.java:162)
    at HeavyThread.run(HeavyThread.java:27)
    at java.lang.Thread.run(Thread.java:619)

"Low Memory Detector" daemon prio=10 tid=0x00007f9a98006800 nid=0x7108 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"CompilerThread1" daemon prio=10 tid=0x00007f9a98004000 nid=0x7107 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"CompilerThread0" daemon prio=10 tid=0x00007f9a98001000 nid=0x7106 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=10 tid=0x0000000040de4000 nid=0x7105 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=10 tid=0x0000000040dc4800 nid=0x7104 in Object.wait() [0x00007f9a97ffe000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00007f9aa45506b0> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118)
    - locked <0x00007f9aa45506b0> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)

"Reference Handler" daemon prio=10 tid=0x0000000040dbd000 nid=0x7103 in Object.wait() [0x00007f9a9de92000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00007f9aa4550318> (a java.lang.ref.Reference$Lock)
    at java.lang.Object.wait(Object.java:485)
    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
    - locked <0x00007f9aa4550318> (a java.lang.ref.Reference$Lock)

"VM Thread" prio=10 tid=0x0000000040db8800 nid=0x7102 runnable 

"GC task thread#0 (ParallelGC)" prio=10 tid=0x0000000040d6e800 nid=0x70fe runnable 

"GC task thread#1 (ParallelGC)" prio=10 tid=0x0000000040d70800 nid=0x70ff runnable 

"GC task thread#2 (ParallelGC)" prio=10 tid=0x0000000040d72000 nid=0x7100 runnable 

"GC task thread#3 (ParallelGC)" prio=10 tid=0x0000000040d74000 nid=0x7101 runnable 

"VM Periodic Task Thread" prio=10 tid=0x00007f9a98011800 nid=0x7109 waiting on condition 

JNI global references: 910

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从我的顶部,我看到顶线程的PID是28938.而28938在十六进制是0x710A.请注意,在堆栈转储中,每个线程都有一个nid以十六进制形式显示的线程.它恰好0x710A是线程的id:

"Thread-0" prio=10 tid=0x00007f9a98020000 nid=0x710a runnable [0x00007f9a9d846000]
   java.lang.Thread.State: RUNNABLE
    at sun.security.provider.DigestBase.engineReset(DigestBase.java:139)
    at sun.security.provider.DigestBase.engineUpdate(DigestBase.java:104)
    at java.security.MessageDigest$Delegate.engineUpdate(MessageDigest.java:538)
    at java.security.MessageDigest.update(MessageDigest.java:293)
    at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:197)
    - locked <0x00007f9aa457e400> (a sun.security.provider.SecureRandom)
    at sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:257)
    - locked <0x00007f9aa457e708> (a java.lang.Object)
    at sun.security.provider.NativePRNG$RandomIO.access$200(NativePRNG.java:108)
    at sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:97)
    at java.security.SecureRandom.nextBytes(SecureRandom.java:433)
    - locked <0x00007f9aa4582fc8> (a java.security.SecureRandom)
    at java.util.UUID.randomUUID(UUID.java:162)
    at HeavyThread.run(HeavyThread.java:27)
    at java.lang.Thread.run(Thread.java:619)

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因此,您可以确认运行HeavyThread该类的线程正在消耗大多数CPU.

在读取世界的情况下,它可能是一堆线程占用CPU的一部分,这些线程放在一起将导致Java进程使用100%的CPU.

摘要

跑顶
按Shift-H启用"线程视图"
获取具有最高CPU的线程的PID
将PID转换为HEX
获取java进程的堆栈转储
查找具有匹配HEX PID的线程.

重要细节:使用小写十六进制表示法 (5认同)
在*nix系统上,我使用_printf 0x%x pid_来获取十六进制值 (3认同)

Answer 2

MRa*_*ser 19

jvmtop可以显示最常用的线程:

    TID NAME                                 STATE     CPU    TOTALCPU
     25 http-8080-Processor13                RUNNABLE  4.55%     1.60%
 128022 RMI TCP Connection(18)-10.101.       RUNNABLE  1.82%     0.02%
  36578 http-8080-Processor164               RUNNABLE  0.91%     2.35%
 128026 JMX server connection timeout   TIMED_WAITING  0.00%     0.00%

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有谁知道这个 TID 如何与线程转储相关联？它们与我在线程转储中看到的“tid”或“nid”标识符不匹配（将它们转换为十六进制后）？ (2认同)

Answer 3

Cow*_*wan 18

尝试查看可视VM的Hot Thread Detector插件 - 它使用ThreadMXBean API获取多个CPU消耗样本以查找最活跃的线程.它基于Bruce Chapman的命令行等效, 也可能有用.

5年后,Bruce Chapman档案的链接不再有效.你仍然可以阅读他的帖子,但不能下载他的任何文件. (5认同)

Answer 4

Law*_*Dol 11

只需运行JVisualVM,连接到您的应用程序并使用线程视图.持续活跃的那个是你最可能的罪魁祸首.

Answer 5

Mar*_*ark 6

看看JConsole 的Top Threads插件.

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