java性能分析

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

1. 通过top命令查看cpu飙升的java进程pid
2. 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
3. 将线程ID号转换为16进程的数值记为tid_hex
4. 使用jdk自带jstack监控命令
5. 使用命令jstack [pid] | grep tid_hex -A100命令输出该线程的堆栈信息
6. 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

1. 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。
2. 已上传github : 点我进入

./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;
mode=0;
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.
  -t, --Top					Using top command to get CPU utilization
  -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
			;;
		-t|--top)
			mode=1
			shift 1
			;;
		-h|--help)
			usage
			exit 0;
			;;
		--)
			shift 1;
			break
			;;
		*)
			shift 1;
			if [ -z "$1" ] ; then
				break
			fi
			;;
		esac
	done
fi
if  [ ! -n "$pid" ] ;then
	echo "error: -p is empty"
	exit 1;
fi

if [ `jps |grep $pid |wc -l` -ne 1 ];then 
	echo "error: -p is wrong"
	exit 1;
fi

function workerByJstack(){
	local tid_hex=$(printf "%x" $tid);
	echo "====================== tid:${tid}  tid_hex:${tid_hex}  cpu:${cpu}  time:${time} ======================";
	jstack $pid | awk 'BEGIN {RS = "

+";ORS = "

"} /'${tid_hex}'/ {print $0}';
	echo "";
}

function workerByTop(){
	top -Hp $pid -n1 | sed '1,7d'| sed '$d' |sed '$d' | sort -k 10 -n -r | sed $[$count+1]',$d' | awk '{print $10,$2,$12}' | while read cpu tid time
	do
		workerByJstack $pid $tid $cpu $time
	done
}

function workerByPs(){
	#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.
	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
		workerByJstack $pid $tid $cpu $time
	done
}

function worker(){
	echo "start-mode:$mode"
	if [ $mode -eq 0 ];then
		workerByPs
	elif [ $mode -eq 1 ];then
		workerByTop
	fi
}
worker