在Linux中找出占用大量CPU的Java代码（将Java线程与Linux PID进行关联）

英文原文：http://blogs.manageengine.com/appmanager/2011/02/09/identify-java-code-consuming-high-cpu-in-linux-linking-jvm-thread-and-linux-pid

在Linux中，我们可以非常方便地找出占用了大量CPU的有问题的Java代码。让我通过下面的例子详细解释一下具体的操作步骤：

package test;
public class ThreadDumpTest {
public void test() {
for (int i = 0; i < 10; i++) {
Thread th = new Thread(new TR(i));
th.setName("MyThread-" + (1000 + i));
th.start();
}
}
public static void main(String[] args) {
ThreadDumpTest t = new ThreadDumpTest();
t.test();
}
private class TR implements Runnable {
int ins = 0;
TR(int i) {
ins = i;
}
public void run() {
while (true) {
if (ins != 5) {
try {
Thread.sleep(10000);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
}

在上面的例子中，所有线程都在执行while循环。除了MyThread-1005

之外，其它线程都会不停地在循环中sleep 10秒钟。MyThread-1005

线程不会进入sleep部分的代码，所以会不停地循环而不做sleep。因为有while循环，所以MyThread-1005

线程会导致很高的CPU利用率。

如何找到占用了大量CPU的线程？

步骤1：

在命令行中执行'top'命令。你会看到一个PID为7074的'java'进程占用了97%的CPU。



步骤2：

'top'命令显示了如上图所示的进程列表。按'shift + h'，等几秒钟。你会看到上面光标的位置出现'Show threads on'的消息字样。现在，你可以看到线程级别的CPU/Memory利用率的详细情况。你可以看到一个java线程，PID是7087使用了97%的CPU。



步骤3：

有问题的线程的PID（7087）是十进制的。把它转换成十六进制
。7087相应的十六进制的值是1BAF。然后转换成小写（1baf）。

步骤4：

做一个Thread Dump（kill -3 7074)，然后在Thread Dump中查找转换出来的十六进制的线程PID（1baf）。你可以找到一个'0x'开头的'nid

'值为1baf（20到22行）。你可以看到正是例子程序中有问题的线程MyThread-1005

。从这个线程的stack trace中，你可以找到有问题的代码然后修复它。

[rameshj@rameshj thread]$ java test/ThreadDumpTest
^/Full thread dump Java HotSpot(TM) Client VM (1.5.0_06-b05 mixed mode):
"DestroyJavaVM" prio=1 tid=0x083d2d78 nid=0x1ba2 waiting on condition [0x00000000..0xbff4bf60]
"MyThread-1009" prio=1 tid=0x08510a88 nid=0x1bb3 waiting on condition [0xa9cca000..0xa9ccb020]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1008" prio=1 tid=0x08510318 nid=0x1bb2 waiting on condition [0xa9d4b000..0xa9d4bea0]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1007" prio=1 tid=0x0850f298 nid=0x1bb1 waiting on condition [0xa9dcc000..0xa9dccf20]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1006" prio=1 tid=0x0850d818 nid=0x1bb0 waiting on condition [0xa9e4d000..0xa9e4dda0]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1005" prio=1 tid=0x0850c9f8 nid=0x1baf runnable [0xa9ece000..0xa9ecee20]
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:43)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1004" prio=1 tid=0x0850b8e8 nid=0x1bae waiting on condition [0xa9f4f000..0xa9f500a0]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1003" prio=1 tid=0x0850aac8 nid=0x1bad waiting on condition [0xa9fd0000..0xa9fd1120]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1002" prio=1 tid=0x085099b8 nid=0x1bac waiting on condition [0xaa051000..0xaa051fa0]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1001" prio=1 tid=0x08508a28 nid=0x1bab waiting on condition [0xaa0d2000..0xaa0d3020]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"MyThread-1000" prio=1 tid=0x08508520 nid=0x1baa waiting on condition [0xaa153000..0xaa153ea0]
at java.lang.Thread.sleep(Native Method)
at test.ThreadDumpTest$TR.run(ThreadDumpTest.java:45)
at java.lang.Thread.run(Thread.java:595)
"Low Memory Detector" daemon prio=1 tid=0x0843cf58 nid=0x1ba8 runnable [0x00000000..0x00000000]
"CompilerThread0" daemon prio=1 tid=0x0843b930 nid=0x1ba7 waiting on condition [0x00000000..0xaa3eb808]
"Signal Dispatcher" daemon prio=1 tid=0x0843a9d0 nid=0x1ba6 waiting on condition [0x00000000..0x00000000]
"Finalizer" daemon prio=1 tid=0x08430740 nid=0x1ba5 in Object.wait() [0xaa52c000..0xaa52d120]
at java.lang.Object.wait(Native Method)
- waiting on <0xaa6b0848> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116)
- locked <0xaa6b0848> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=1 tid=0x0842e898 nid=0x1ba4 in Object.wait() [0xaa5ad000..0xaa5adfa0]
at java.lang.Object.wait(Native Method)
- waiting on <0xaa6b0758> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:474)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
- locked <0xaa6b0758> (a java.lang.ref.Reference$Lock)
"VM Thread" prio=1 tid=0x0842bb68 nid=0x1ba3 runnable
"VM Periodic Task Thread" prio=1 tid=0x0843e538 nid=0x1ba9 waiting on condition

- Ramesh