What is the php multi-process function?

When running scripts on the server, some time-consuming tasks cannot be avoided, and the use of multiple processes is essential. After PHP5.5, PHP began to add multi-process elements to meet development needs.

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php multi-process is generally used to execute php scripts in the php_cli command line to implement expansions that need to be enabled for multiple processes: pcntl, posix (pcntl is the abbreviation of process control process management) . Multi-process programming of PHP is not supported in the Windows environment. This article is mainly developed and tested in the Linux environment.

pcntl_fork — Generates a branch (child process) at the current position of the current process.
Basic example of a fork sub-process:

$pid = pcntl_fork();
//父进程和子进程都会执行下面代码
if ($pid == -1) {
        //错误处理：创建子进程失败时返回-1.
         die('could not fork');
} else if ($pid) {
         //父进程会得到子进程号，所以这里是父进程执行的逻辑
         pcntl_wait($status); //等待子进程中断，防止子进程成为僵尸进程。
} else {
         //子进程得到的$pid为0, 所以这里是子进程执行的逻辑。
}

If a task is broken down into multiple processes for execution, the overall time-consuming will be reduced.
For example, there is a relatively large data file to be processed. This file consists of many lines. If a single process executes the tasks to be processed, it will take a long time if the volume is large. At this time, multiple processes can be considered.

Let’s look at an interview question. There is an int array with 10 million elements that needs to be summed. It is divided equally into 4 processes for processing. Each process processes a part, and then the results are counted. The code is as follows

  <?php

  $arrint = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];//假设很多
  $arrint = array_chunk($arrint,4,TRUE);
  for ($i = 0; $i < 4; $i++){
      	$pid = pcntl_fork();
  if ($pid == -1) {
     	die("could not fork");
  } elseif ($pid) {
      	echo $pid;
      	echo "I'm the Parent $i\n";
  } else {
       	// 子进程处理
      	// $content = file_get_contents("prefix_name0".$i);
     	$psum = array_sum($arrint[$i]);
      	echo $psum . "\n";分别输出子进程的部分求和数字，但是无法进行想加，因为进程互相独立
     	exit;// 一定要注意退出子进程,否则pcntl_fork() 会被子进程再fork,带来处理上的影响。
       	}
  }
          
  // 等待子进程执行结
  while (pcntl_waitpid(0, $status) != -1) {
      	$status = pcntl_wexitstatus($status);
      	echo "Child $status completed\n";
  }

In the appeal answer, the array is divided into 4 sub-arrays and processed by 4 sub-processes respectively. However, there is no way to add the calculated results because the processes complete the tasks independently and there is no way to share the same process. A (memory) variable, message queue will be introduced below to solve the problem of process communication

  <?php
  $arrint = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];//假设很多
  $arrint = array_chunk($arrint,4,TRUE);//把数组分为4个

  // 创建消息队列,以及定义消息类型(类似于数据库中的库)
  $id = ftok(__FILE__,'m');//生成文件key，唯一
  $msgQueue = msg_get_queue($id);
  const MSG_TYPE = 1;
  msg_send($msgQueue,MSG_TYPE,'0');//给消息队列一个默认值0，必须是字符串类型
  
  //fork出四个子进程
  for ($i = 0; $i < 4; $i++){
   		$pid = pcntl_fork();
      	if ($pid == -1) {
          	die("could not fork");
      	} elseif ($pid) {
         	echo $pid;
          	echo "I'm the Parent $i\n";
      	} else {
      		// 子进程处理逻辑，相互独立，解决办法，放到内存消息队列中
          	$part = array_sum($arrint[$i]);
          	implode_sum($part);//合成计算出的sum
          	exit;// 一定要注意退出子进程,否则pcntl_fork() 会被子进程再fork,带来处理上的影响。
    	}
  }
          
  function implode_sum($part){
     	global $msgQueue;
      	msg_receive($msgQueue,MSG_TYPE,$msgType,1024,$sum);//获取消息队列中的值，最后一个参数为队列中的值
      	$sum = intval($sum) + $part;
      	msg_send($msgQueue,MSG_TYPE,$sum);//发送每次计算的结果给消息队列
  }
      
  // 等待子进程执行结束
  while (pcntl_waitpid(0, $status) != -1) {
      	$status = pcntl_wexitstatus($status);
      	$pid = posix_getpid();
      	echo "Child $status completed\n";
  }
      
  //所有子进程结束后，再取出最后在队列中的值，就是int数组的和
  msg_receive($msgQueue,MSG_TYPE,$msgType,1024,$sum);
  echo $sum;//输出120

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