shell里如何实现‘多线程’?

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代码:

job_1
job_2
job_2
.....
job_100

引用:

-(dearvoid@LinuxEden:Forum)-(~/tmp)-
[$$=6718 $?=0] ; cat job_1
#!/bin/bash

n=$((RANDOM % 5 + 1))
echo "$0 sleeping for $n seconds ..."
sleep $n
echo "$0 exiting ..."
-(dearvoid@LinuxEden:Forum)-(~/tmp)-
[$$=6718 $?=0] ; for ((i = 2; i <= 10; ++i)); do cp job_1 job_$i; done
-(dearvoid@LinuxEden:Forum)-(~/tmp)-
[$$=6718 $?=0] ; cat jobs.sh
#!/bin/bash

nParellel=5
nJobs=10
sJobPattern='./job_%d'

aJobs=()
sNextJob=
for ((iNextJob = 1; iNextJob <= nJobs; )); do
    for ((iJob = 0; iJob < nParellel; ++iJob)); do
        if [ $iNextJob -gt $nJobs ]; then
            break;
        fi

        if [ ! "${aJobs[iJob]}" ] || ! kill -0 ${aJobs[iJob]} 2> /dev/null; then
            printf -v sNextJob "$sJobPattern" $((iNextJob++))
            echo "$sNextJob starting ..."
            $sNextJob &
            aJobs[iJob]=$!
        fi
    done
    sleep .1
done

wait
-(dearvoid@LinuxEden:Forum)-(~/tmp)-
[$$=6718 $?=0] ; ./jobs.sh
./job_1 starting ...
./job_1 sleeping for 3 seconds ...
./job_2 starting ...
./job_2 sleeping for 2 seconds ...
./job_3 starting ...
./job_3 sleeping for 5 seconds ...
./job_4 starting ...
./job_5 starting ...
./job_4 sleeping for 4 seconds ...
./job_5 sleeping for 2 seconds ...
./job_2 exiting ...
./job_6 starting ...
./job_6 sleeping for 2 seconds ...
./job_5 exiting ...
./job_7 starting ...
./job_7 sleeping for 1 seconds ...
./job_1 exiting ...
./job_8 starting ...
./job_8 sleeping for 3 seconds ...
./job_7 exiting ...
./job_9 starting ...
./job_9 sleeping for 5 seconds ...
./job_4 exiting ...
./job_6 exiting ...
./job_10 starting ...
./job_10 sleeping for 5 seconds ...
./job_3 exiting ...
./job_8 exiting ...
./job_9 exiting ...
./job_10 exiting ...
-(dearvoid@LinuxEden:Forum)-(~/tmp)-
[$$=6718 $?=0] ; bye

引用:

原帖由 mygod100 于 2008.6.25 11:21 发表
有些地方没看懂啊，还请指教一下
1. 第6行, aJobs=()是什么意思，声明一个空函数？
2. ${aJobs} 是取aJobs的PID吗？
3.  aJobs=$! 也不知道是什么意思

能否稍微解释一下，谢谢!