parallel.sh

#!/bin/bash
# author: thinkycx
# date: 2019-01-14
# Usage:
#     run jobs at the same time with multiple process.
parallel(){
    nCPU=3 # 同时执行的进程数量
    PID=()

    for((i=0;i<5;i++)){
        # while process number >= nCPU
        echo "============================================"
        # echo "[*] PID() len: " ${#PID[*]}
        echo "[*] PID() content:" ${PID[*]}

        # echo "[-] Checking PID() length >= nCPU ?"
        while [ ${#PID[*]} -ge $nCPU ] ;
        do
            for pid in ${PID[*]}; do
                ps -p $pid >/dev/null
                isQuit=$?
                if [ $isQuit -eq 1 ] ; then
                    PID=(${PID[*]/$pid})
                    echo "[*] Checking... $pid stops. PID() len: " ${#PID[*]}
                fi
            done
            sleep 1;
        done
        # echo "[*] After check. " ${PID[*]}

        # start new process background
        (
            echo -e "\\t [x] Job $i start to run..."
            sleep 5
            echo -e "\\t [x] Job $i done. "

        )&
        PID[$i]=$!               # 向数组中添加上一个运行的后台进程的pid
        sleep 1
        echo -e "\\t [*] process PID is :" ${PID[$i]}

    }
}

parallel
wait
echo "[*] Congratilations. All jobs done! "