如何在生产服务器中确定哪个Java线程消耗了最多的CPU。
大多数（如果不是全部）执行重要任务的生产系统将使用多个Java线程。当有问题发生并且CPU使用率达到100％时，很难确定哪个线程（或哪些线程）造成了这种情况。直到有人比我聪明地向我展示了如何完成它。在这里，我将向您展示如何做到这一点，以便您也可以通过您的极客技能惊叹您的家人和朋友。
一个测试应用程序
为了进行测试，我们需要一个测试应用程序。我会提供一个给你。它由三个类组成：
- 一个
HeavyThread类，用于执行一些CPU密集型操作（计算MD5哈希值）
- 一个
LightThread类，用于执行一些不那么CPU密集型的操作（计数和睡眠）。
- 一个
StartThreads类，用于启动1个CPU密集型和多个轻型线程。
以下是这些类的代码：
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;
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 = "";
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);
}
digest.update(data.getBytes());
}
}
}
import java.util.Random;
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;
}
}
}
}
public class StartThreads {
public static void main(String[] args) {
new HeavyThread(1000);
new LightThread();
new LightThread();
new LightThread();
}
}
假设你从未见过这段代码，你手头只有一个运行这些类并且占用100％ CPU 的Java进程的PID。
首先让我们从StartThreads类开始。
$ ls
HeavyThread.java LightThread.java StartThreads.java
$ javac *
$ java StartThreads &
目前有一个Java进程正在运行，它应该占用了100%的CPU。在我的top命令中，我看到：
在top命令中按Shift-H键，可以打开线程信息。top命令的man手册中写道：
-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.
现在我打开了Threads显示功能，在顶部看到如下截图：
我有一个PID为28294的java进程。使用jstack获取该进程的堆栈转储：
$ 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$Lock)
"VM Thread" prio=10 tid=0x0000000040db8800 nid=0x7102 runnable
"GC task thread#0 (ParallelGC)" prio=10 tid=0x0000000040d6e800 nid=0x70fe runnable
"GC task thread#1 (ParallelGC)" prio=10 tid=0x0000000040d70800 nid=0x70ff runnable
"GC task thread#2 (ParallelGC)" prio=10 tid=0x0000000040d72000 nid=0x7100 runnable
"GC task thread#3 (ParallelGC)" prio=10 tid=0x0000000040d74000 nid=0x7101 runnable
"VM Periodic Task Thread" prio=10 tid=0x00007f9a98011800 nid=0x7109 waiting on condition
JNI global references: 910
从我的顶部我可以看到顶级线程的PID是
28938。而
28938以十六进制表示是
0x710A。请注意，在堆栈转储中，每个线程都有一个以十六进制表示的
nid。恰好
0x710A是该线程的ID。
"Thread-0" prio=10 tid=0x00007f9a98020000 nid=0x710a runnable [0x00007f9a9d846000]
java.lang.Thread.State: RUNNABLE
at sun.security.provider.DigestBase.engineReset(DigestBase.java:139)
at sun.security.provider.DigestBase.engineUpdate(DigestBase.java:104)
at java.security.MessageDigest$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)
因此，您可以确认运行 HeavyThread 类的线程正在消耗大部分 CPU。
在实际情况中，可能是一堆线程消耗了一部分 CPU，这些线程加在一起会导致 Java 进程使用 100% 的 CPU。
摘要
- 运行 top 命令
- 按 Shift-H 查看线程视图
- 获取具有最高 CPU 的线程的进程 ID
- 将进程 ID 转换为十六进制
- 获取 Java 进程的堆栈转储
- 查找具有匹配十六进制 PID 的线程。
