Many Java daemons are multi threaded. If some program shows high cpu usage, how will you analyze it? I’m showing the tip based on Linux environment.
1) Detect problemetic thread
Usually linux “top” shows total cpu usage of a process. Therefore we need to separate problematic thread. While running top, press “H” or start top with -H option. Then PID column shows thread id.
2) Map the thread with source code
To detect problematic class, make thread dump of the process.
#kill -3 process_id (Do not use thread id, but use process id)
Now, I’m showing a sample.
<High cpu thread class>
<Idle thread class>
<Test main class>
When I run TestMain.class, top shows high cpu usage. (Process mode)
Process id 13906’s cpu usage is high. Next I change into thread mode. (with “H” option)
This top shows that thread id 13936 is the root cause of the problem. Now I make thread dump with following command.
# kill -3 13906 (Do not type in 13936)
The following is thread dump.
|Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.121-b13 mixed mode):
“Thread-1” #11 prio=5 os_prio=0 tid=0x00007f1b1c124800 nid=0x3671 in Object.wait() [0x00007f1b08236000]
“Thread-0” #10 prio=5 os_prio=0 tid=0x00007f1b1c123000 nid=0x3670 runnable [0x00007f1b08337000]
“main” #1 prio=5 os_prio=0 tid=0x00007f1b1c009000 nid=0x3657 in Object.wait() [0x00007f1b22e12000]
At first, you can not find string “13936”. Java thread dump shows thread id in hexa decimal. 13936’s hexa decimal value is 3670 and you can find the line.
“Thread-0” #10 prio=5 os_prio=0 tid=0x00007f1b1c123000 nid=0x3670 runnable
(nid means native thread id. More detailed explanation)
Now we found the problemetic class (BusyThread.java).