本文將簡述如何快速瞭解 PHP 的多進程編程，並提供實驗腳本。
函數
為快速入門，本文只使用多進程的兩個函數：pcntl_fork 和 pcntl_waitpid
多進程開發最重要的函數 pcntl_fork，其在當前進程 fork 一個子進程，然後父子進程在 fork 處分別繼續向下執行。
這裡需要注意，pcntl_fork 返回的值在父進程會得到子進程的 PID （進程 ID），而在子進程中，該值為 ``。
實例
接著開始實踐，執行 pcntl.php 腳本：
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}
