背景
有处理过生产问题的同学基本都能遇到系统忽然缓慢，CPU突然飙升，甚至整个应用请求不可用。当出现这种情况下，在不影响数据准确性的前提下，我们应该尽快导出jstack和内存信息，然后重启系统，尽快回复系统的可用性，避免用户体验过差。本文针对CPU飙升问题，提供该问题的排查思路，从而能够快速定位到某线程甚至某快代码导致CPU飙升，从而提供处理该问题的思路。
排查过程
通过top命令查看cpu飙升的java进程pid
通过ps -mp [pid] -o THREAD,tid,time查看该进程下所拥有的线程及各个线程占用cpu的使用率，并且记录CPU使用率过高的线程ID号
将线程ID号转换为16进程的数值记为tid_hex
使用jdk自带jstack监控命令
使用命令jstack [pid] | grep tid_hex -A100命令输出该线程的堆栈信息
根据堆栈信息分析代码。
通过以上步骤可以查找出导致cpu飙升的相关代码位置，然后对代码进行code review即可。
工具封装
以上步骤已经封装为脚本文件,通过以下脚本文件只需要指定进程ID即pid即可导出默认前5条导致CPU率过高的堆栈信息。
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./java-thread-top.sh -p pid
#!/bin/bash
# @Function
# Find out the highest cpu consumed threads of java processes, and print the stack of these threads.
# @github https://github.com/cjunn/script_tool/
# @author cjunn
# @date Sun Jan 12 2020 21:08:58 GMT+0800
#
pid='';
count=5;
function usage(){
readonly PROG="`basename $0`"
cat <<EOF
Usage: ${PROG} [OPTION]
Find out the highest cpu consumed threads of java processes,
and print the stack of these threads.
Example:
${PROG} -p <pid> -c 5 # show top 5 busy java threads info
Output control:
-p, --pid <java pid> find out the highest cpu consumed threads from
the specified java process.
default from all java process.
-c, --count <num> set the thread count to show, default is 5.
Miscellaneous:
-h, --help display this help and exit.
EOF
}
#1.Collect script parameters
#2.Check whether PID exists
if [ $# -gt 0 ];
then
while true; do
case "$1" in
-c|--count)
count="$2"
shift 2
;;
-p|--pid)
pid="$2"
shift 2
;;
-h|--help)
usage
exit 0;
;;
--)
shift
break
;;
*)
shift
if [ -z "$1" ] ; then
break
fi
;;
esac
done
fi
if [ ! -n "$pid" ] ;then
echo "error: -p is empty"
exit 1;
fi
function worker(){
#1.Query all threads according to PID.
#2.Delete header and first line information.
#3.According to the second column of CPU to sort, reverse display.
#4.Delete the count + 1 to last column based on the count value.
#5.Get CPU utilization, TID value, thread used time, and assign them to CPU, TID, time respectively.
#6.Perform hex conversion on TID.
#7.Use JDK to monitor all threads of jstack output PID.
#8.Use awk to regularly query the thread information of tid_hex required.
#9.Display the stack information of count before thread busy.
local whilec=0;
ps -mp $pid -o THREAD,tid,time | sed '1,2d' | sort -k 2 -n -r |sed $[$count+1]',$d' | awk '{print $2,$8,$9}' | while read cpu tid time
do
tid_hex=$(printf "%x" $tid);
echo "====================== tid:${tid} tid_hex:${tid_hex} cpu:${cpu} time:${time} ======================";
jstack $pid | awk 'BEGIN {RS = "\n\n+";ORS = "\n\n"} /'${tid_hex}'/ {print $0}'
echo "";
whilec=$[$whilec+1];
done
if [ $whilec -eq 0 ] ; then
echo "error : thread not found, make sure pid exists.";
fi
}
worker
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