Laravel 源码学习笔记 7：服务提供者-延迟加载的触发
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之前有[laravel源码学习笔记4：kernel实例解析request请求]文章有稍微对服务提供者过了一遍，在启动容器的时候，会去根据config的providers来获取全部的服务提供者，然后会对比缓存文件cache/services.php来决定哪些是需要立即注册的服务，哪些是延迟加载的。
cache/services.php文件中，返回了一个数组，大概内容是这样
<?php return array (
'providers' =>
array (
0 => 'Illuminate\\Auth\\AuthServiceProvider',
1 => 'Illuminate\\Broadcasting\\BroadcastServiceProvider',
2 => 'Illuminate\\Bus\\BusServiceProvider',
...
),
'eager' =>
array (
0 => 'Illuminate\\Auth\\AuthServiceProvider',
1 => 'Illuminate\\Cookie\\CookieServiceProvider',
...
),
'deferred' =>
array (
'Illuminate\\Broadcasting\\BroadcastManager' => 'Illuminate\\Broadcasting\\BroadcastServiceProvider',
'Illuminate\\Contracts\\Broadcasting\\Factory' => 'Illuminate\\Broadcasting\\BroadcastServiceProvider',
'Illuminate\\Contracts\\Broadcasting\\Broadcaster' => 'Illuminate\\Broadcasting\\BroadcastServiceProvider',
...
),
'when' =>
array (
'Illuminate\\Broadcasting\\BroadcastServiceProvider' => array (
),
)
);数据比较多，就先注释了一部分，可以看到返回了四个键，分别是
- providers(全部的服务提供者)
- eager(框架启动立即注册的服务)
- deferred(延迟加载的服务)
- when(触发延迟加载的监听事件)
其中eager立即注册，也就是添加实现依赖，没啥好说，主要来聊聊延迟加载的服务deferred
为什么需要延迟加载？
一些不常用的服务，不需要每次都准备好，生意可以设置为当需要的时候才去加载解析服务实例，这样可以提升框架加载性能，节省内存。
何时触发延迟加载的服务？
需要用到这个服务的时候
如何触发延迟加载的服务？
- app(xxx)直接make解析出实例，大部分时候应该也是用这种方法
- 事件监听注册服务
主要聊聊这个事件监听注册服务的方法，之前看到when个数组的时候，就很好奇，这个到底是干嘛的，因为和eager还有deferred放在同一层数组上了，以为也是个加载服务的形式，后来看了里面服务对应了延迟加载里的服务，就猜测可能是用来触发延迟加载的，看代码
ProviderRepository.php
public function load(array $providers)
{
//缓存文件的内容
$manifest = $this->loadManifest();
// First we will load the service manifest, which contains information on all
// service providers registered with the application and which services it
// provides. This is used to know which services are "deferred" loaders.
// 是否重新载入provider缓存文件
if ($this->shouldRecompile($manifest, $providers)) {
//重载后的的里面文件的数组信息
$manifest = $this->compileManifest($providers);
}
// dd($manifest);
// Next, we will register events to load the providers for each of the events
// that it has requested. This allows the service provider to defer itself
// while still getting automatically loaded when a certain event occurs.
// 根据监听触发的延迟加载
foreach ($manifest['when'] as $provider => $events) {
$this->registerLoadEvents($provider, $events);
}
// We will go ahead and register all of the eagerly loaded providers with the
// application so their services can be registered with the application as
// a provided service. Then we will set the deferred service list on it..
// eager立即加载的服务
foreach ($manifest['eager'] as $provider) {
$this->app->register($provider);
}
//把需要延迟加载的服务添加进app容器的deferredServices数组
$this->app->addDeferredServices($manifest['deferred']);
}在注册服务的时候会执行load方法，里面的变量$manifest会根据不同键来做不同的服务处理，当有when的时候
foreach ($manifest['when'] as $provider => $events) {
$this->registerLoadEvents($provider, $events);
}
protected function registerLoadEvents($provider, array $events)
{
Log::info('$provider'.json_encode([$provider]),[$events]);
if (count($events) < 1) {
return;
}
Log::info('cout event > 1 '.json_encode([$provider]),[$events]);
$this->app->make('events')->listen($events, function () use ($provider) {
Log::info('registerLoadEvents-register',[$provider]);
$this->app->register($provider);
});
}里面会去遍历服务对面的array里的内容，然后去做一个监听，然鹅我们看上面贴的services.php 里的when数组，对应的值都是空的，也就是，这里他不会去注册任何的监听，那when下的服务对应的数组里的内容是哪里来的呢？，我们看之前的compileManifest方法
if ($this->shouldRecompile($manifest, $providers)) {
//重载后的的里面文件的数组信息
$manifest = $this->compileManifest($providers);
}
protected function compileManifest($providers)
{
// The service manifest should contain a list of all of the providers for
// the application so we can compare it on each request to the service
// and determine if the manifest should be recompiled or is current.
$manifest = $this->freshManifest($providers);
// dd($providers);
// Illuminate\Broadcasting\BroadcastServiceProvider
foreach ($providers as $provider) {
$instance = $this->createProvider($provider);
if ($provider == 'Illuminate\Broadcasting\BroadcastServiceProvider'){
// dd($instance,$instance->provides());
}
// When recompiling the service manifest, we will spin through each of the
// providers and check if it's a deferred provider or not. If so we'll
// add it's provided services to the manifest and note the provider.
// 看provider里的defer 是否为true，是就是延迟加载
if ($instance->isDeferred()) {
foreach ($instance->provides() as $service) {
$manifest['deferred'][$service] = $provider;
}
$manifest['when'][$provider] = $instance->when();
}
// If the service providers are not deferred, we will simply add it to an
// array of eagerly loaded providers that will get registered on every
// request to this application instead of "lazy" loading every time.
// 立即加载
else {
$manifest['eager'][] = $provider;
}
}
return $this->writeManifest($manifest);
}compileManifest方法中，会根据传进去的providers数组，组装$manifest变量的内容
if ($instance->isDeferred()) {
foreach ($instance->provides() as $service) {
$manifest['deferred'][$service] = $provider;
}
$manifest['when'][$provider] = $instance->when();
}可以看到会根据$instance->isDeferred()这个实例的defer属性，如果是true就会丢进deferred数组里，下面还有一行
$manifest['when'][$provider] = $instance->when();这个应该就是赋予when下服务对应的array数组的值，再去创建对应的监听了，那会发现$instance->when()这个方法哪里来呢？我们随便找之前services.php的文件里的一个延迟服务Illuminate\Broadcasting\BroadcastServiceProvider
里面的内容是
class BroadcastServiceProvider extends ServiceProvider
{
/**
* Indicates if loading of the provider is deferred.
*
* @var bool
*/
protected $defer = true;
/**
* Register the service provider.
*
* @return void
*/
public function register()
{
Log::info('BroadcastServiceProvider-regist');
$this->app->singleton(BroadcastManager::class, function ($app) {
return new BroadcastManager($app);
});
$this->app->singleton(BroadcasterContract::class, function ($app) {
return $app->make(BroadcastManager::class)->connection();
});
$this->app->alias(
BroadcastManager::class, BroadcastingFactory::class
);
}
/**
* Get the services provided by the provider.
*
* @return array
*/
public function provides()
{
return [
BroadcastManager::class,
BroadcastingFactory::class,
BroadcasterContract::class,
];
}
)这里有绑定的方法，provides方法返回三个不同的实现类，那when方法在哪呢？我们可以看到这个provider继承的是ServiceProvider点进去发现了when方法！
/**
* Get the events that trigger this service provider to register.
*
* @return array
*/
public function when()
{
return [];
}看注释可以知道，这个是为了触发服务注册的，那我们在BroadcastServiceProvider中重写这个不就可以了？试试
class BroadcastServiceProvider extends ServiceProvider
{
protected $defer = true;
public function register()
{
...
}
public function provides()
{
...
}
public function when()
{
Log::info('BroadcastServiceProvider-when');
// return [];
return ['BroadcastServiceProvider-event'];
}
}我们返回了一个数组，里面算是我们自定义的监听名称，然后我们再随便再对框架进行个请求(http://blog.test/test)发现services.php 有东西了！
'when' =>
array (
'Illuminate\\Broadcasting\\BroadcastServiceProvider' =>
array (
0 => 'BroadcastServiceProvider-event',
),也就是，在上面的registerLoadEvents方法中，我们应该注册了这个服务的监听！
这时候我们在控制器中测试下
class TestController extends Controller
{
//
public function test(){
// $cache = App::make(Cache::class);
Event::fire('BroadcastServiceProvider-event'); //注册进容器，单例绑定
dd(\app();
$bm1 = App::make(BroadcastManager::class); // 注册容器后，绑定后，返回这个单例的实例
$bm2 = App::make(BroadcasterContract::class); // 注册容器后，绑定后，返回这个单例的实例
dd($bm2);
}
如控制器所示，发送请求后，用event的fire方法监听，这时候dd容器，会发现里面就会有BroadcastServiceProvider，和下面的app直接make解析，也会注册，感兴趣的可以自己试下~
有什么不对或有疑问的地方请大佬们指正:)
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