Analyzing PHP multi-process programming

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PHP Multi-Process Programming

Advantages of using multiple processes:

    1. 使用多进程, 子进程结束以后, 内核会负责回收资源
    2. 使用多进程,子进程异常退出不会导致整个进程Thread退出. 父进程还有机会重建流程.
    3. 一个常驻主进程, 只负责任务分发, 逻辑更清楚.

To implement multi-process in PHP, Let's Go.

We need to install the pcnt extension

pcntl is the abbreviation of process control. Usually, PHP will install this extension by default. Use the phpinfo() function to check whether the extension exists.

Use the pcntl_fork() function to create a child process

The function of pcntl_fork is to create a child process that is the same as the current process. The code segment of this child process is exactly the same as the current process. , but has its own data segment. Let’s look at the simplest way to create a child process:

<?php /**
 *  hedong
 * @date 2017-04-03
 */

$parentPid = getmypid(); // 获取父进程id $childPid = pcntl_fork(); // 创建子进程 switch($childPid) {
    case -1:
        print "创建子进程失败!".PHP_EOL;
        exit;
    case 0:
        print "我是子进程，进程ID：{$childPid}".PHP_EOL;
        break;
    default:
        print "我是父进程，进程ID：{$parentPid},子进程ID: {$childPid}".PHP_EOL;
}
?>

pcntl_fork()调用成功以后，一个程序变成了两个程序：一个程序得到的$pid变量值是0，它是子进程；另一个程序得到的$pid的值大于0，这个值是子进程的PID，它是父进程。

Output result:

Subprocess recycling

① Blocking method
Did you get any ps just now? Generally, I am used to using ps aux plus grep command to find running background processes. There is a column STAT, which identifies the running status of each process. Here, we focus on state Z: Zombie. When the child process exits before the parent process and the parent process does not do anything with it, the child process will become a zombie process. Although zombie processes do not occupy much memory, they are an eyesore. (Don't forget that they still occupy the PID)

Generally speaking, just recycle the hung child process before the parent process ends. There is a pcntl_wait() function in the pcntl extension. This method waits for the process to end and then recycles the ended process.

<?php /**
 *  hedong
 * @date 2017-04-03
 */

$parentPid = getmypid(); // 获取父进程id $childPid = pcntl_fork(); // 创建子进程 switch($childPid) {
    case -1:
        print "创建子进程失败!".PHP_EOL;
        exit;
    case 0:
        print "我是子进程，进程ID：{$childPid}".PHP_EOL;
        break;
    default:
        pcntl_wait($status); // 子进程执行完后才执行父进程         print "我是父进程，进程ID：{$parentPid},子进程ID: {$childPid}".PHP_EOL;
}

② Non-blocking method
The blocking method loses the parallelism of multiple processes. There is also a way to recycle the completed child process and parallelize it. This is the non-blocking way.

<?php /**
 *  hedong
 * @date 2017-04-03
 */

for ($i = 1; $i <= 5; ++$i) {
    $pid = pcntl_fork(); // 创建子进程

    if (!$pid) {
        sleep(1);
        print "In child $i\n";
        exit($i);
    }
}

// pcntl_waitpid 第一个参数为 0 代表处理全部子进程

while (pcntl_waitpid(0, $status) != -1) {
    $status = pcntl_wexitstatus($status);
    echo "Child $status completed\n";
}

What if the parent process hangs first?

what happens? Nothing happens, the child process is still running. But at this time, the child process will be handed over to process No. 1, and process No. 1 becomes the stepfather of these child processes. Process No. 1 will take good care of the resources of these processes, and Process No. 1 will automatically reclaim the resources when they end. So, another temporary way to deal with zombie processes is to shut down their parent process.

Final note:

Process control cannot be applied in a Web server environment. It may bring unexpected results when used in a Web service environment. -- Excerpted from the PHP manual

Reference:

http://www.hackingwithphp.com/16/1/3/getting-into-multiprocessing

http://www.jb51.net/article/71232.htm

http://www.laruence.com/2009/06/11/930.html

http://imhuchao.com/596.html

https://www.pureweber.com/article/php-multi-process-programming-preview/

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