背景

        有處理過生產問題的同學基本都能遇到系統忽然緩慢，CPU突然飆升，甚至整個應用請求不可用。當出現這種情況下，在不影響數據準確性的前提下，我們應該儘快導出jstack和記憶體信息，然後重啟系統，儘快回覆系統的可用性，避免用戶體驗過差。本文針對CPU飆升問題，提供該問題的排查思路，從而能夠快速定位到某線程甚至某快代碼導致CPU飆升，從而提供處理該問題的思路。

排查過程

1. 通過top命令查看cpu飆升的java進程pid
2. 通過ps -mp [pid] -o THREAD,tid,time查看該進程下所擁有的線程及各個線程占用cpu的使用率，並且記錄CPU使用率過高的線程ID號
3. 將線程ID號轉換為16進程的數值記為tid_hex
4. 使用jdk自帶jstack監控命令
5. 使用命令jstack [pid] | grep tid_hex -A100命令輸出該線程的堆棧信息
6. 根據堆棧信息分析代碼。

通過以上步驟可以查找出導致cpu飆升的相關代碼位置，然後對代碼進行code review即可。

工具封裝

1. 以上步驟已經封裝為腳本文件,通過以下腳本文件只需要指定進程ID即pid即可導出預設前5條導致CPU率過高的堆棧信息。
2. 已上傳github : 點我進入

./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