PHP幾種回調寫法

PHP 裡通過匿名函數寫回調是最方便的，但除了匿名函數方式的回調，PHP 還有其它的回調寫法。以下是 PHP 幾種回調寫法的範例。

1、匿名函數回調

<?php
use Workerman\Worker;
use Workerman\Connection\TcpConnection;
use Workerman\Protocols\Http\Request;
require_once __DIR__ . '/vendor/autoload.php';

$http_worker = new Worker("http://0.0.0.0:2345");

// 匿名函數回調
$http_worker->onMessage = function(TcpConnection $connection, Request $data)
{
    // 向瀏覽器發送 hello world
    $connection->send('hello world');
};

Worker::runAll();

2、普通函數回調

<?php
use Workerman\Worker;
use Workerman\Connection\TcpConnection;
use Workerman\Protocols\Http\Request;
require_once __DIR__ . '/vendor/autoload.php';

$http_worker = new Worker("http://0.0.0.0:2345");

// 匿名函數回調
$http_worker->onMessage = 'on_message';

// 普通函數
function on_message(TcpConnection $connection, Request $request)
{
    // 向瀏覽器發送 hello world
    $connection->send('hello world');
}

Worker::runAll();

3、類方法作為回調

MyClass.php

use Workerman\Worker;
use Workerman\Connection\TcpConnection;
class MyClass{
    public function __construct(){}
    public function onWorkerStart(Worker $worker){}
    public function onConnect(TcpConnection $connection){}
    public function onMessage(TcpConnection $connection, $message) {}
    public function onClose(TcpConnection $connection){}
    public function onWorkerStop(Worker $worker){}
}

啟動腳本 start.php

<?php
use Workerman\Worker;
require_once __DIR__ . '/vendor/autoload.php';

// 载入 MyClass
require_once __DIR__.'/MyClass.php';

$worker = new Worker("websocket://0.0.0.0:2346");

// 創建一個對象
$my_object = new MyClass();

// 調用類的方法
$worker->onWorkerStart = array($my_object, 'onWorkerStart');
$worker->onConnect     = array($my_object, 'onConnect');
$worker->onMessage     = array($my_object, 'onMessage');
$worker->onClose       = array($my_object, 'onClose');
$worker->onWorkerStop  = array($my_object, 'onWorkerStop');

Worker::runAll();

注意：
以上的代碼結構不允許在建構函數裡初始化資源（MySQL 連接、Redis 連接、Memcache 連接等），因為 $my_object = new MyClass(); 運行在主進程。以 MySQL 為例，在主進程初始化的 MySQL 連接等資源會被子進程繼承，每個子進程都可以操作這個資料庫連接，但這些連接在 MySQL 服務端對應的是同一個連接，會發生不可預期的錯誤，例如 mysql gone away 錯誤。

以上代碼結構如果需要在類的建構函數裡初始化資源，可以採用以下寫法。
MyClass.php

use Workerman\Worker;
use Workerman\Connection\TcpConnection;
class MyClass{
    protected $db = null;
    public function __construct(){
        // 假設資料庫連接類是 MyDbClass
        $db = new MyDbClass();
    }
    public function onWorkerStart(Worker $worker){}
    public function onConnect(TcpConnection $connection){}
    public function onMessage(TcpConnection $connection, $message) {}
    public function onClose(TcpConnection $connection){}
    public function onWorkerStop(Worker $worker){}
}

啟動腳本 start.php

<?php
use Workerman\Worker;
require_once __DIR__ . '/vendor/autoload.php';

$worker = new Worker("websocket://0.0.0.0:2346");

// 在 onWorkerStart 裡初始化類
$worker->onWorkerStart = function($worker) {
    // 载入 MyClass
    require_once __DIR__.'/MyClass.php';

    // 創建一個對象
    $my_object = new MyClass();

    // 調用類的方法
    $worker->onConnect    = array($my_object, 'onConnect');
    $worker->onMessage    = array($my_object, 'onMessage');
    $worker->onClose      = array($my_object, 'onClose');
    $worker->onWorkerStop = array($my_object, 'onWorkerStop');
};

Worker::runAll();

上面代碼結構中 onWorkerStart 運行時已經是屬於子進程，等於每個子進程各自建立自己的 MySQL 連接，所以不會有共享連接的問題。
這樣還有一個好處就是支持業務代碼 reload。因為 MyClass.php 是在子進程載入的，根據 reload 規則業務更改 MyClass.php 後直接 reload 即可生效。

4、類的靜態方法作為回調

靜態類 MyClass.php

use Workerman\Worker;
use Workerman\Connection\TcpConnection;
class MyClass{
    public static function onWorkerStart(Worker $worker){}
    public static function onConnect(TcpConnection $connection){}
    public static function onMessage(TcpConnection $connection, $message) {}
    public static function onClose(TcpConnection $connection){}
    public static function onWorkerStop(Worker $worker){}
}

啟動腳本 start.php

<?php
use Workerman\Worker;
require_once __DIR__ . '/vendor/autoload.php';

// 载入 MyClass
require_once __DIR__.'/MyClass.php';

$worker = new Worker("websocket://0.0.0.0:2346");

// 調用類的靜態方法。
$worker->onWorkerStart = array('MyClass', 'onWorkerStart');
$worker->onConnect     = array('MyClass', 'onConnect');
$worker->onMessage     = array('MyClass', 'onMessage');
$worker->onClose       = array('MyClass', 'onClose');
$worker->onWorkerStop  = array('MyClass', 'onWorkerStop');

// 如果類帶命名空間，則是類似這樣的寫法
// $worker->onWorkerStart = array('your\namesapce\MyClass', 'onWorkerStart');
// $worker->onConnect     = array('your\namesapce\MyClass', 'onConnect');
// $worker->onMessage     = array('your\namesapce\MyClass', 'onMessage');
// $worker->onClose       = array('your\namesapce\MyClass', 'onClose');
// $worker->onWorkerStop  = array('your\namesapce\MyClass', 'onWorkerStop');

Worker::runAll();

注意：根據 PHP 的運行機制，如果沒用調用 new 則不會調用建構函數，另外靜態類的方法裡不允許使用 $this。