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如何定位消耗CPU最多的线程

之前有朋友反馈说发的内容希望有个梯度，逐步加深，前面发了几篇关于jvm源码分析的文章，可能我觉得我已经把内容写得浅显易懂了，但是对于某些没怎么接触的同学来说还是比较难理解，这个我以后慢慢改进吧，今天发篇轻松点的文章，可能大家在工作过程中也会可能碰到类似的问题，或许有经验的同学看到这个题目就知道我要说什么了，也有自己的定位方法。

话不多说了，先来看代码吧

public class Test{         public static void main(String args[]){                 for(int i=0;i<10;i++){                         new Thread(){                                 public void run(){                                         try{                                                 Thread.sleep(100000);                                         }catch(Exception e){}                                 }                         }.start();                 }                 Thread t=new Thread(){                         public void run(){                                 int i=0;                                 while(true){                                         i=(i++)/100;                                 }                         }                 };                 t.setName("Busiest Thread");                 t.start();         } }

这个例子里新创建了11个线程，其中10个线程没干什么事，主要是sleep，另外有一个线程在循环里一直跑着，可以想象这个线程是这个进程里最耗cpu的线程了，那怎么把这个线程给抓出来呢？

首先我们可以通过 top -Hp <pid> 来看这个进程里所有线程的cpu消耗情况，得到类似下面的数据

$ top -Hp 18207 top - 19:11:43 up 573 days,  2:43,  2 users,  load average: 3.03, 3.03, 3.02 Tasks:  44 total,   1 running,  43 sleeping,   0 stopped,   0 zombie Cpu(s): 18.8%us,  0.0%sy,  0.0%ni, 81.1%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st Mem:  99191752k total, 98683576k used,   508176k free,   128248k buffers Swap:  1999864k total,   191064k used,  1808800k free, 17413760k cached    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 18250 admin     20   0 26.1g  28m  10m R 99.9  0.0   0:19.50 java Test 18207 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18208 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.09 java Test 18209 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18210 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18211 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18212 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18213 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18214 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18215 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18216 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18217 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18218 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18219 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18220 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18221 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18222 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18223 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18224 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18225 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18226 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test 18227 admin     20   0 26.1g  28m  10m S  0.0  0.0   0:00.00 java Test

拿到这个结果之后，我们可以看到cpu最高的线程是pid为18250的线程，占了99.9%：

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 18250 admin     20   0 26.1g  28m  10m R 99.9  0.0   0:19.50 java Test

接着我们可以通过 jstack <pid> 的输出来看各个线程栈:

$ jstack 18207 2016-03-30 19:12:23 Full thread dump OpenJDK 64-Bit Server VM (25.66-b60 mixed mode):  "Attach Listener" #30 daemon prio=9 os_prio=0 tid=0x00007fb90be13000 nid=0x47d7 waiting on condition [0x0000000000000000]    java.lang.Thread.State: RUNNABLE  "DestroyJavaVM" #29 prio=5 os_prio=0 tid=0x00007fb96245b800 nid=0x4720 waiting on condition [0x0000000000000000]    java.lang.Thread.State: RUNNABLE  "Busiest Thread" #28 prio=5 os_prio=0 tid=0x00007fb91498d000 nid=0x474a runnable [0x00007fb9065fe000]    java.lang.Thread.State: RUNNABLE   at Test$2.run(Test.java:18)  "Thread-9" #27 prio=5 os_prio=0 tid=0x00007fb91498c800 nid=0x4749 waiting on condition [0x00007fb906bfe000]    java.lang.Thread.State: TIMED_WAITING (sleeping)   at java.lang.Thread.sleep(Native Method)   at Test$1.run(Test.java:9)  "Thread-8" #26 prio=5 os_prio=0 tid=0x00007fb91498b800 nid=0x4748 waiting on condition [0x00007fb906ffe000]    java.lang.Thread.State: TIMED_WAITING (sleeping)   at java.lang.Thread.sleep(Native Method)   at Test$1.run(Test.java:9)  "Thread-7" #25 prio=5 os_prio=0 tid=0x00007fb91498b000 nid=0x4747 waiting on condition [0x00007fb9073fe000]    java.lang.Thread.State: TIMED_WAITING (sleeping)   at java.lang.Thread.sleep(Native Method)   at Test$1.run(Test.java:9)  "Thread-6" #24 prio=5 os_prio=0 tid=0x00007fb91498a000 nid=0x4746 waiting on condition [0x00007fb9077fe000]    java.lang.Thread.State: TIMED_WAITING (sleeping)   at java.lang.Thread.sleep(Native Method)   at Test$1.run(Test.java:9) ...

上面的线程栈我们注意到nid的值其实就是线程ID，它是十六进制的，我们将消耗cpu最高的线程 18250 ，转成十六进制 0x474a ，然后从上面的线程栈里找到 nid=0x474a 的线程，其栈为：

 "Busiest Thread" #28 prio=5 os_prio=0 tid=0x00007fb91498d000 nid=0x474a runnable [0x00007fb9065fe000]    java.lang.Thread.State: RUNNABLE   at Test$2.run(Test.java:18)

即将最耗cpu的线程找出来了，是 Businest Thread