use linux top command and the jdk utility jstack to find which java thread consumes most CPU

top_jstack_thread_cpu.md

use top command to find which java thread consume high CPU

Using the following command to find what java threads consume high CPU

$ top -n1 -p <pid> -H

Tasks:  47 total,   0 running,  47 sleeping,   0 stopped,   0 zombie
Cpu(s): 22.1%us,  2.2%sy,  0.0%ni, 74.8%id,  0.0%wa,  0.0%hi,  0.9%si,  0.0%st
Mem:  32955308k total,  4727936k used, 28227372k free,   723000k buffers
Swap: 16875512k total,        0k used, 16875512k free,  3022092k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
22784 nls       24  -1 2430m  45m 9900 S  90.0 0.1   0:00.00 java
22791 nls       18  -1 2430m  45m 9900 S  0.0  0.1   0:00.29 java
22792 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22793 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22794 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22795 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22796 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22797 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22798 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22799 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java
22800 nls       17  -1 2430m  45m 9900 S  0.0  0.1   0:00.00 java

From the above top command output, we know the thread 22784 consume high cpu. Convert the number 22784 to hex

$ printf "%x" 22784
5900

so the thread is 5900

dump the java thread stack using jstack

$jstack -l <pid>

find the thread 5900 and the output looks like below:

...

"Thread-11" #62 prio=5 os_prio=0 tid=0x60b45400 nid=0x5900 runnable [0x60776000]
   java.lang.Thread.State: RUNNABLE

...