本文将简述如何快速了解 PHP 的多进程编程，并提供实验脚本。
函数
为快速入门，本文只使用多进程的两个函数：pcntl_fork 和 pcntl_waitpid
多进程开发最重要的函数 pcntl_fork，其在当前进程 fork 一个子进程，然后父子进程在 fork 处分别继续向下执行。
这里需要注意，pcntl_fork 返回的值在父进程会得到子进程的 PID （进程 ID），而在子进程中，该值为 ``。
实例
接着开始实践，执行 pcntl.php 脚本：
1$ php ./pcntl.php
2
3Child process #7217 started
4Child process #7218 started
5Child process #7218 finished
6Child process #7220 started
7Child process #7221 started
8Child process #7219 started
9Child process #7221 finished
10Child process #7217 finished
11Child process #7220 finished
12Child process #7219 finished
13Child process #7217 exited with status: 0
14Child process #7218 exited with status: 0
15Child process #7219 exited with status: 0
16Child process #7220 exited with status: 0
17Child process #7221 exited with status: 0
pcntl.php
1<?php
2
3if (!extension_loaded('pcntl')) {
4 die("Extension not loaded: pcntl\n");
5}
6
7$workers = [];
8$workersCount = 5;
9
10for ($i = 0; $i < $workersCount; $i++) {
11 $pid = pcntl_fork();
12 if ($pid < 0) {
13 die("Could not fork\n");
14 }
15 if ($pid > 0) {
16 // parent process
17 $workers[] = $pid; // store child process ID.
18 continue;
19 }
20
21 // child process
22 $pid = posix_getpid();
23 echo "Child process #{$pid} started\n";
24
25 // task
26 sleep(rand(0, 2));
27
28 echo "Child process #{$pid} finished\n";
29
30 // exit on child process has finished it's task.
31 exit(0);
32}
33
34// parent process
35foreach ($workers as $worker) {
36 // wait child process to exit
37 pcntl_waitpid($worker, $status);
38 echo "Child process #{$worker} exited with status: {$status}\n";
39}
