> 线上的一个日志实时输出的程序曾经出过这样一个问题，刚开始上线java程序占用的`CPU`的资源很少,但是到了整点的时候,CPU直线飙高，直接到达`100%`根本没有要下降的趋势，唯一的方法只能杀掉它了，后面在借助`jstack`与`top`排查到线程然后定位到某行代码出的问题。
## 排查演示
1. 使用`jps`找到程序的`pid`
```
[root@logs bin]# ./jps -l -m | grep logdir2
22169 galaxy-log-online-0.1-SNAPSHOT-all.jar 3002 /logdir2
```
2. 找到`22169`进程ID
3. 找到CPU过高的线程
```
top -H -p 22169
top - 19:03:22 up 156 days, 5:57, 4 users, load average: 1.00, 2.84, 4.25
Threads: 15 total, 0 running, 15 sleeping, 0 stopped, 0 zombie
%Cpu(s): 99.4 us, 12.6 sy, 0.0 ni, 62.6 id, 4.8 wa, 0.0 hi, 2.6 si, 0.0 st
KiB Mem : 8010456 total, 206760 free, 1079668 used, 6724028 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 6561460 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
22184 root 20 0 4543356 74148 12960 S 80.0 40.9 0:19.96 java
22169 root 20 0 4543356 74148 12960 S 0.0 0.9 0:00.00 java
22170 root 20 0 4543356 74148 12960 S 0.0 0.9 0:00.35 java
22171 root 20 0 4543356 74148 12960 S 0.0 0.9 0:00.08 java
22172 root 20 0 4543356 74148 12960 S 0.0 0.9 0:00.09 java
...
```
4. 将线程转为16进制
```
[root@logs bin]# printf "%x" 22184
56a8
```
5. 使用`jstack`定位到线程
```
[root@logs bin]# ./jstack 22169 | grep 56a8
"Thread-1" #9 prio=5 os_prio=0 tid=0x00007fe428230800 nid=0x56a8 waiting on condition [0x00007fe4121a5000]
```
6. 使用`3D`肉眼来查看线程运行的代码了
```
"Thread-1" #9 prio=5 os_prio=0 tid=0x00007fe428230800 nid=0x56a8 waiting on condition [0x00007fe4121a5000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at java.lang.Thread.sleep(Unknown Source)
at java.util.concurrent.TimeUnit.sleep(Unknown Source)
at com.dounine.tool.http.sql.LogsRequest$4.run(LogsRequest.java:152)
at java.lang.Thread.run(Unknown Source)
```
然后开始从`LogsRequest.java`152行开始找起，发现里面有一个死循环...
## FIX 它
然后开开心心下班
