10. 容器的 singleton 和 bind 的实现

[xiaohuilam]

容器的 singleton 和 bind 方法在整个 Laravel 框架或扩展中是调用的比较频繁的底层方法，掌握其原理能帮助我们加深 laravel 容器的理解。

初识

singleton() 代码

单身狗模式

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 338 to 348 in d081c91

	/**
	* Register a shared binding in the container.
	*
	* @param string $abstract
	* @param \Closure|string|null $concrete
	* @return void
	*/
	public function singleton($abstract, $concrete = null)
	{
	$this->bind($abstract, $concrete, true);
	}

bind() 代码

分裂模式

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 206 to 240 in d081c91

	/**
	* Register a binding with the container.
	*
	* @param string $abstract
	* @param \Closure|string|null $concrete
	* @param bool $shared
	* @return void
	*/
	public function bind($abstract, $concrete = null, $shared = false)
	{
	// If no concrete type was given, we will simply set the concrete type to the
	// abstract type. After that, the concrete type to be registered as shared
	// without being forced to state their classes in both of the parameters.
	$this->dropStaleInstances($abstract);
	if (is_null($concrete)) {
	$concrete = $abstract;
	}
	// If the factory is not a Closure, it means it is just a class name which is
	// bound into this container to the abstract type and we will just wrap it
	// up inside its own Closure to give us more convenience when extending.
	if (! $concrete instanceof Closure) {
	$concrete = $this->getClosure($abstract, $concrete);
	}
	$this->bindings[$abstract] = compact('concrete', 'shared');
	// If the abstract type was already resolved in this container we'll fire the
	// rebound listener so that any objects which have already gotten resolved
	// can have their copy of the object updated via the listener callbacks.
	if ($this->resolved($abstract)) {
	$this->rebound($abstract);
	}
	}

初略看二者差异可能看不大出来。
我们从他们暴露的接口入手，先用，再啪（扒）源码。

调试

祭出大杀器：php artisan tinker

bind

>>> app()->bind('test', function(){dump(1); return new \StdClass();});
1
=> null
>>>
>>> app()->make('test')
1
=> {#2895}
>>>
>>> app()->make('test')
1
=> {#2896}

可以看出，调用 bind 时，每次取出被绑定的对象时，都会重新去构建一次。

如果用singleton 呢。

singleton

>>> app()->singleton('test', function(){dump(1); return new \StdClass();});
1
=> null
>>> app()->make('test')
=> {#2915}
>>> app()->make('test')
=> {#2915}
>>>

分析

bind 的实质，容器中捆绑

我们回头再看下 bind() 方法

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 206 to 240 in d081c91

	/**
	* Register a binding with the container.
	*
	* @param string $abstract
	* @param \Closure|string|null $concrete
	* @param bool $shared
	* @return void
	*/
	public function bind($abstract, $concrete = null, $shared = false)
	{
	// If no concrete type was given, we will simply set the concrete type to the
	// abstract type. After that, the concrete type to be registered as shared
	// without being forced to state their classes in both of the parameters.
	$this->dropStaleInstances($abstract);
	if (is_null($concrete)) {
	$concrete = $abstract;
	}
	// If the factory is not a Closure, it means it is just a class name which is
	// bound into this container to the abstract type and we will just wrap it
	// up inside its own Closure to give us more convenience when extending.
	if (! $concrete instanceof Closure) {
	$concrete = $this->getClosure($abstract, $concrete);
	}
	$this->bindings[$abstract] = compact('concrete', 'shared');
	// If the abstract type was already resolved in this container we'll fire the
	// rebound listener so that any objects which have already gotten resolved
	// can have their copy of the object updated via the listener callbacks.
	if ($this->resolved($abstract)) {
	$this->rebound($abstract);
	}
	}

逻辑步骤为:

• 参数依次为 $abstract、$concrete
• dropStaleInstances 移除之前 bind 过的 $abstract 的数据（旧的 $concret）
• 如果没有传 $concrete，则将 $concrete 设置成 $abstract
• 如果为闭包 如果不为闭包（感谢 @HubQin 的指正），则通过 Container::getClosure() 方法将闭包改成一个接受 $container、$parameters 的包裹后的闭包。此闭包实质就是在需要运行的时候，运行闭包。
• 将 Container::$bindings 数组 $abstract 为 key 的值设置为 compact('concrete', 'shared')，即 ["concrete" => $concrete, "shared" => $shared]
• 如果 bind 的对象已经 resolved 过了，通过 Container::rebound() 触发 reboundCallbacks 中的回调。

---

到目前为止，暂时还没看出 $share 对 singleton 和 bind 的影响。只知道 bind 在执行过程中，将 $shared 和 $concrete 一起存到了 Container::$bindings 中。

用句四川话，莫慌，我们马上就要揭开关键的面纱了。。。

揭开 Container::make() 神秘的面纱

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 592 to 602 in d081c91

	/**
	* Resolve the given type from the container.
	*
	* @param string $abstract
	* @param array $parameters
	* @return mixed
	*/
	public function make($abstract, array $parameters = [])
	{
	return $this->resolve($abstract, $parameters);
	}

其实 make 是直接透传给了 resolve

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 616 to 675 in d081c91

	/**
	* Resolve the given type from the container.
	*
	* @param string $abstract
	* @param array $parameters
	* @return mixed
	*/
	protected function resolve($abstract, $parameters = [])
	{
	$abstract = $this->getAlias($abstract);
	$needsContextualBuild = ! empty($parameters) || ! is_null(
	$this->getContextualConcrete($abstract)
	);
	// If an instance of the type is currently being managed as a singleton we'll
	// just return an existing instance instead of instantiating new instances
	// so the developer can keep using the same objects instance every time.
	if (isset($this->instances[$abstract]) && ! $needsContextualBuild) {
	return $this->instances[$abstract];
	}
	$this->with[] = $parameters;
	$concrete = $this->getConcrete($abstract);
	// We're ready to instantiate an instance of the concrete type registered for
	// the binding. This will instantiate the types, as well as resolve any of
	// its "nested" dependencies recursively until all have gotten resolved.
	if ($this->isBuildable($concrete, $abstract)) {
	$object = $this->build($concrete);
	} else {
	$object = $this->make($concrete);
	}
	// If we defined any extenders for this type, we'll need to spin through them
	// and apply them to the object being built. This allows for the extension
	// of services, such as changing configuration or decorating the object.
	foreach ($this->getExtenders($abstract) as $extender) {
	$object = $extender($object, $this);
	}
	// If the requested type is registered as a singleton we'll want to cache off
	// the instances in "memory" so we can return it later without creating an
	// entirely new instance of an object on each subsequent request for it.
	if ($this->isShared($abstract) && ! $needsContextualBuild) {
	$this->instances[$abstract] = $object;
	}
	$this->fireResolvingCallbacks($abstract, $object);
	// Before returning, we will also set the resolved flag to "true" and pop off
	// the parameter overrides for this build. After those two things are done
	// we will be ready to return back the fully constructed class instance.
	$this->resolved[$abstract] = true;
	array_pop($this->with);
	return $object;
	}

第一步骤的

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Line 625 in d081c91

$abstract = $this->getAlias($abstract);

是做了森么呢？
还原用 Container::alias() 方法设置过别名的原始 $abstract。

下一步，

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 627 to 629 in d081c91

	$needsContextualBuild = ! empty($parameters) || ! is_null(
	$this->getContextualConcrete($abstract)
	);

Container::getContextualConcrete() 其实是取这里设置进取的 上下文绑定 的数据

laravel/vendor/laravel/framework/src/Illuminate/Container/ContextualBindingBuilder.php

Lines 56 to 67 in d081c91

	/**
	* Define the implementation for the contextual binding.
	*
	* @param \Closure|string $implementation
	* @return void
	*/
	public function give($implementation)
	{
	$this->container->addContextualBinding(
	$this->concrete, $this->needs, $implementation
	);
	}

ContextualBindingBuilder::give() 暂时就不在这里暂开研究了。咱们继续往下看

$needsContextualBuild 值为 make() 方法是否传了第二个参数，也就是 $parameters。 needs contextual build 意思是

构建时，是否具有上下文关联性

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 634 to 636 in d081c91

	if (isset($this->instances[$abstract]) && ! $needsContextualBuild) {
	return $this->instances[$abstract];
	}

判断 Container::$instances 数组中是否能通过 $abstract 找到对象。如果找得到且不具有上下文关联性，就用之前创建好的对象。

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 638 to 640 in d081c91

	$this->with[] = $parameters;
	$concrete = $this->getConcrete($abstract);

getConcrete() 代码为

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 680 to 697 in d081c91

	* @param string $abstract
	* @return mixed $concrete
	*/
	protected function getConcrete($abstract)
	{
	if (! is_null($concrete = $this->getContextualConcrete($abstract))) {
	return $concrete;
	}
	// If we don't have a registered resolver or concrete for the type, we'll just
	// assume each type is a concrete name and will attempt to resolve it as is
	// since the container should be able to resolve concretes automatically.
	if (isset($this->bindings[$abstract])) {
	return $this->bindings[$abstract]['concrete'];
	}
	return $abstract;
	}

相信你能看出来 return $this->bindings[$abstract]['concrete'] ，就是根据 $abstract 把前面 bind 或 singleton 的数据返回。

这里的 isBuildable 是判断 $abstract 是否与 $concrete 一致或 $concrete 为闭包

如果不是，那么可能是还有递归调用，需要再走一次 make

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 645 to 649 in d081c91

	if ($this->isBuildable($concrete, $abstract)) {
	$object = $this->build($concrete);
	} else {
	$object = $this->make($concrete);
	}

645 行调用的 isBuildable()

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 745 to 748 in d081c91

	protected function isBuildable($concrete, $abstract)
	{
	return $concrete === $abstract || $concrete instanceof Closure;
	}

接着调用了 Container::build() 方法

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 758 to 801 in d081c91

	public function build($concrete)
	{
	// If the concrete type is actually a Closure, we will just execute it and
	// hand back the results of the functions, which allows functions to be
	// used as resolvers for more fine-tuned resolution of these objects.
	if ($concrete instanceof Closure) {
	return $concrete($this, $this->getLastParameterOverride());
	}
	$reflector = new ReflectionClass($concrete);
	// If the type is not instantiable, the developer is attempting to resolve
	// an abstract type such as an Interface of Abstract Class and there is
	// no binding registered for the abstractions so we need to bail out.
	if (! $reflector->isInstantiable()) {
	return $this->notInstantiable($concrete);
	}
	$this->buildStack[] = $concrete;
	$constructor = $reflector->getConstructor();
	// If there are no constructors, that means there are no dependencies then
	// we can just resolve the instances of the objects right away, without
	// resolving any other types or dependencies out of these containers.
	if (is_null($constructor)) {
	array_pop($this->buildStack);
	return new $concrete;
	}
	$dependencies = $constructor->getParameters();
	// Once we have all the constructor's parameters we can create each of the
	// dependency instances and then use the reflection instances to make a
	// new instance of this class, injecting the created dependencies in.
	$instances = $this->resolveDependencies(
	$dependencies
	);
	array_pop($this->buildStack);
	return $reflector->newInstanceArgs($instances);
	}

其中的

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Line 767 in d081c91

$reflector = new ReflectionClass($concrete);

和

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 789 to 800 in d081c91

	$dependencies = $constructor->getParameters();
	// Once we have all the constructor's parameters we can create each of the
	// dependency instances and then use the reflection instances to make a
	// new instance of this class, injecting the created dependencies in.
	$instances = $this->resolveDependencies(
	$dependencies
	);
	array_pop($this->buildStack);
	return $reflector->newInstanceArgs($instances);

是通过反射解析待构建类所需参数中其他对象参数，从容器中取出填入。

再往下面就是执行 Container::extend 设置的扩充流程了。

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 654 to 656 in d081c91

	foreach ($this->getExtenders($abstract) as $extender) {
	$object = $extender($object, $this);
	}

再后面，才是对我们 singleton() 和 bind() 产生深远影响的代码：

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 661 to 663 in d081c91

	if ($this->isShared($abstract) && ! $needsContextualBuild) {
	$this->instances[$abstract] = $object;
	}

我们在前面知道，如果为 singleton() 执行到 resolve() 的第二个参数 $shared 为 true, bind 为 false。
前面 $needsContextualBuild 判断的位置，判断了 Container::$instance 中是否有 $abstract， 所以在这里如果 resolve 没有将 $object 绑入 Container::$instance，那么下次 Container::make() 依旧会在去 build() 一次，这就产生了 singleton() 和 bind()的特性。

再接着，就是触发事件了。

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Line 665 in d081c91

$this->fireResolvingCallbacks($abstract, $object);

最后是一些收尾工作

laravel/vendor/laravel/framework/src/Illuminate/Container/Container.php

Lines 670 to 674 in d081c91

	$this->resolved[$abstract] = true;
	array_pop($this->with);
	return $object;

此章节为什么叫做单身狗呢？因为 Container::make() 严格遵守 $shared，如果声明了 true，他保证不搞一个分身（所以是单身）给你。

[HubQin]

bind的分析，'如果为闭包' 应该是 '如果不是闭包' 吧？因为程序是 if (! $concrete instanceof Closure)

[xiaohuilam]

bind的分析，'如果为闭包' 应该是 '如果不是闭包' 吧？因为程序是 if (! $concrete instanceof Closure)

是的，打错了