linux里查看最耗CPU的線程

1、top后按c查看最耗cpu的進程，得到pid

2、top -Hp pid 查看該進程里的線程資源使用情況，找到最耗資源的線程的pid

3、jstack pid來查看進程的各個線程棧，注意這里的pid是第一步中進程的pid，不是第二步得到的線程id

4、將第二步得到的pid轉成16進制之后在線程棧信息里查找nid等于pid16進制的，就找到最耗資源的線程的棧信息

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話不多說了，先來看代碼吧

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();}
}

這個例子里新創建了11個線程，其中10個線程沒干什么事，主要是sleep，另外有一個線程在循環里一直跑著，可以想象這個線程是這個進程里最耗cpu的線程了，那怎么把這個線程給抓出來呢？

首先我們可以通過top -Hp <pid>來看這個進程里所有線程的cpu消耗情況，得到類似下面的數據

$ 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 cachedPID 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

拿到這個結果之后，我們可以看到cpu最高的線程是pid為18250的線程，占了99.8%：

 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

接著我們可以通過jstack <pid>的輸出來看各個線程棧:

$ 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: RUNNABLEat 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)
...

上面的線程棧我們注意到nid的值其實就是線程ID，它是十六進制的，我們將消耗cpu最高的線程18250，轉成十六進制0X47A，然后從上面的線程棧里找到nid=0X47A的線程，其棧為：

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

即將最耗cpu的線程找出來了，是Businest Thread