php:多进程执行任务

需求

对指定数量的多个任务并发执行，并控制进程数

进程&线程：

进程间相互独立，不影响。

代码示例：

<?php

$task = 0; //任务id
$taskNum = 10; //任务总数
$processNumLimit = 2; //子进程总量限制

while(true){
   //产生分支
   $processid = pcntl_fork();

   //创建子进程失败
   if( $processid == -1 ){
       echo "create process error！\n";
       exit(1);
   }
   //主进程，获得子进程pid
   elseif($processid){
       $task++; //下一个任务

       $currentProcessid = posix_getpid(); //当前进程的Id
       $parentProcessid = posix_getppid(); // 父级进程的ID
       $phpProcessid = getmypid(); //当前php进程的id
       echo "task:",$task,"\tprocessid:",$processid,"\tcurrentProcessid:",$currentProcessid,"\tparentProcessid:",$parentProcessid,"\tphpProcessid:",$phpProcessid,"\n";

       //控制进程数
       if($task >= $processNumLimit) {
           echo "wait chl start！\n";
           $exitid = pcntl_wait($status); //等待退出
           echo "wait chl end！extid:",$exitid,"\tstatus:",$status,"\n";
       }
       
       //任务总量控制
       if($task >= $taskNum) {
           echo "taskNum enough！\n";
           break;
       }
   }
   //processid=0为新创建的进程
   else{
       //模拟不同任务的不同执行时长
       $sleep = rand(1, 5);

       $currentProcessid = posix_getpid(); //当前进程的Id
       $parentProcessid = posix_getppid(); // 父级进程的ID
       $phpProcessid = getmypid(); //当前php进程的id
       echo "task:",$task,"\tprocessid:",$processid,"\tcurrentProcessid:",$currentProcessid,"\tparentProcessid:",$parentProcessid,"\tphpProcessid:",$phpProcessid,"\tsleep:",$sleep,"\tbegin!\n";

       sleep($sleep);

       echo "task:",$task,"\tprocessid:",$processid,"\tcurrentProcessid:",$currentProcessid,"\tparentProcessid:",$parentProcessid,"\tphpProcessid:",$phpProcessid,"\tsleep:",$sleep,"\tend!\n";
       
       exit(0); //子进程执行完后退出，防止进入循环创建子进程
   }
}

执行的结果：

task:1    processid:32225    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
task:0    processid:0    currentProcessid:32225    parentProcessid:32224    phpProcessid:32225    sleep:5    begin!
task:2    processid:32226    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:1    processid:0    currentProcessid:32226    parentProcessid:32224    phpProcessid:32226    sleep:2    begin!
task:1    processid:0    currentProcessid:32226    parentProcessid:32224    phpProcessid:32226    sleep:2    end!
wait chl end！extid:32226    status:0
task:3    processid:32228    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:2    processid:0    currentProcessid:32228    parentProcessid:32224    phpProcessid:32228    sleep:1    begin!
task:2    processid:0    currentProcessid:32228    parentProcessid:32224    phpProcessid:32228    sleep:1    end!
wait chl end！extid:32228    status:0
task:4    processid:32229    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:3    processid:0    currentProcessid:32229    parentProcessid:32224    phpProcessid:32229    sleep:2    begin!
task:0    processid:0    currentProcessid:32225    parentProcessid:32224    phpProcessid:32225    sleep:5    end!
wait chl end！extid:32225    status:0
task:5    processid:32270    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:4    processid:0    currentProcessid:32270    parentProcessid:32224    phpProcessid:32270    sleep:1    begin!
task:3    processid:0    currentProcessid:32229    parentProcessid:32224    phpProcessid:32229    sleep:2    end!
wait chl end！extid:32229    status:0
task:6    processid:32271    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:5    processid:0    currentProcessid:32271    parentProcessid:32224    phpProcessid:32271    sleep:4    begin!
task:4    processid:0    currentProcessid:32270    parentProcessid:32224    phpProcessid:32270    sleep:1    end!
wait chl end！extid:32270    status:0
task:7    processid:32273    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:6    processid:0    currentProcessid:32273    parentProcessid:32224    phpProcessid:32273    sleep:1    begin!
task:6    processid:0    currentProcessid:32273    parentProcessid:32224    phpProcessid:32273    sleep:1    end!
wait chl end！extid:32273    status:0
task:8    processid:32274    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:7    processid:0    currentProcessid:32274    parentProcessid:32224    phpProcessid:32274    sleep:2    begin!
task:5    processid:0    currentProcessid:32271    parentProcessid:32224    phpProcessid:32271    sleep:4    end!
task:7    processid:0    currentProcessid:32274    parentProcessid:32224    phpProcessid:32274    sleep:2    end!
wait chl end！extid:32274    status:0
task:9    processid:32277    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
wait chl end！extid:32271    status:0
task:8    processid:0    currentProcessid:32277    parentProcessid:32224    phpProcessid:32277    sleep:2    begin!
task:10    processid:32278    currentProcessid:32224    parentProcessid:15053    phpProcessid:32224
wait chl start！
task:9    processid:0    currentProcessid:32278    parentProcessid:32224    phpProcessid:32278    sleep:2    begin!
task:8    processid:0    currentProcessid:32277    parentProcessid:32224    phpProcessid:32277    sleep:2    end!
task:9    processid:0    currentProcessid:32278    parentProcessid:32224    phpProcessid:32278    sleep:2    end!
wait chl end！extid:32277    status:0
taskNum enough

执行分析：

1. 在pcntl_fork出创建子进程后，子进程执行功能代码，父进程继续递增任务id，创建下一个任务进程；
2. 通过pcntl_wait等待有子进程执行完毕退出后，再新创建进程，实现进程总数的控制；
3. 在主进程完成创建后，通过break退出循环。此时可能有子进程继续执行。

相关函数：

pcntl_fork

在当前进程当前位置产生分支（子进程）。成功时，在父进程执行线程内返回产生的子进程的PID，在子进程执行线程内返回0。失败时，在 父进程上下文返回-1，不会创建子进程，并且会引发一个PHP错误。

pcntl_wait

等待或返回fork的子进程状态。wait函数刮起当前进程的执行直到一个子进程退出或接收到一个信号要求中断当前进程或调用一个信号处理函数。 如果一个子进程在调用此函数时已经退出（俗称僵尸进程），此函数立刻返回。子进程使用的所有系统资源将 被释放。

其他：

1.僵尸进程及孤儿进程的问题

部分僵尸进程被pcntl_wait获取状态并释放资源，未接管的进程在主进程退出后成为孤儿进程。孤儿进程被init进程收养，完成wait的状态获取和资源释放。