jstack使用教程

1. qmq是部署在tomcat中的應用名
ps -ef | grep qmq | grep -v grep

拿到進程號， 例如上面對應的是3192
2. 第二步找出該進程內最耗費CPU的線程，可以使用ps -Lfp pid或者ps -mp pid -o THREAD, tid, time或者top -Hp pid
例如用第三個 top -Hp 3192

Tasks: 123 total,   0 running, 123 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.3%us,  0.4%sy,  0.0%ni, 99.3%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   3922688k total,  3272588k used,   650100k free,   432768k buffers
Swap:  4194296k total,        0k used,  4194296k free,   596488k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 3494 tomcat    20   0 4905m 1.1g  11m S  0.3 28.4   0:51.91 java
 3551 tomcat    20   0 4905m 1.1g  11m S  0.3 28.4   4:46.32 java
 3588 tomcat    20   0 4905m 1.1g  11m S  0.3 28.4   0:07.35 java
 3192 tomcat    20   0 4905m 1.1g  11m S  0.0 28.4   0:00.00 java
 3194 tomcat    20   0 4905m 1.1g  11m S  0.0 28.4   0:00.82 java

3. TIME列就是各個Java線程耗費的CPU時間，CPU時間最長的是線程ID為3551的線程，用
printf "%x\n" 3551
得到ddf

4. sudo -u tomcat jstack 3192 | grep ddf

"New I/O worker #30" daemon prio=10 tid=0x00007f44fd525800 nid=0xde4 runnable [0x00007f4530ddf000]
"DubboResponseTimeoutScanTimer" daemon prio=10 tid=0x00007f44fca88000 nid=0xddf waiting on condition [0x00007f45322e5000]