哪个 Java 线程占用了 CPU？

multithreading java cpu

2022-08-31 13:46:10

假设您的Java程序占用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程：

运行，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 - 。最好将jstack的输出重定向到文件。jstack <pid>jps
搜索“可运行”线程。跳过那些在套接字上等待的（由于某种原因，它们仍然被标记为可运行）。
重复步骤 1 和 2 几次，看看是否可以找到模式。

或者，您可以在 Eclipse 中附加到 Java 进程，并尝试逐个挂起线程，直到遇到占用 CPU 的线程。在单 CPU 计算机上，您可能需要首先降低 Java 进程的优先级才能四处移动。即便如此，由于超时，Eclipse 通常也无法附加到正在运行的进程。

我本来以为Sun的工具会做到这一点。visualvm

有谁知道更好的方法吗？

答案 1

确定哪个 Java 线程在生产服务器中消耗了最多的 CPU。

大多数（如果不是全部）生产系统做任何重要的事情都会使用超过1个java线程。当某些事情变得疯狂并且您的CPU使用率为100%时，很难确定哪个线程正在/正在导致这种情况。至少我是这么想的。直到有人比我更聪明，向我展示了如何做到这一点。在这里，我将向您展示如何做到这一点，您也可以用您的极客技能让您的家人和朋友感到惊讶。

测试应用程序

为了测试这一点，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：

执行 CPU 密集型操作（计算 MD5 哈希）的类HeavyThread
执行不那么CPU密集型操作（计数和睡眠）的类。LightThread
启动 1 个 CPU 密集型和多个轻量级线程的类。StartThreads

下面是这些类的代码：

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();
        }
}

假设您从未见过此代码，并且您只有一个失控的Java进程的PID，该进程正在运行这些类并消耗100%的CPU。

首先，让我们开始上课。StartThreads

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

在此阶段，正在运行的 Java 进程应占用 100 个 cpu。在我的顶部，我看到： screenshot of top output

在顶部按 Shift-H 打开线程。顶部的手册页显示：

   -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.

现在在我的顶部，线程显示打开，我看到： top screenshot with threads displayed

我有一个PID的过程。让我们使用以下命令获取此过程的堆栈转储：java28294jstack

$ 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

从我的顶部，我看到顶部线程的PID是。在十六进制中是.请注意，在堆栈转储中，每个线程都有一个以十六进制表示的线程。碰巧的是线程的id：28938289380x710Anid0x710A

"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)

因此，您可以确认运行该类的线程消耗了大部分 CPU。HeavyThread

在阅读世界的情况下，它可能是一堆线程消耗一部分CPU，这些线程放在一起将导致Java进程使用100%CPU。

总结

运行顶部
按 Shift-H 以启用“线程”视图
获取具有最高 CPU 的线程的 PID
将 PID 转换为十六进制
获取 Java 进程的堆栈转储
查找具有匹配的十六进制 PID 的螺纹。

答案 2

jvmtop 可以向你显示消耗最多的线程：

    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%