php - __destruct() 和 __call() 创建无限循环

Question

我大大简化了我的代码，但我正在做的是这样的:

class App{

    protected $apps = [];

    public function __construct($name, $dependencies){
        $this->name = $name;

        $apps = [];
        foreach($dependencies as $dependName){
            $apps[$name] = $dependName($this); // returns an instance of App
        }
        $this->apps = $apps;
    }

    public function __destruct(){
        foreach($this->apps as $dep){
            $result = $dep->cleanup($this);
        }
    }

    public function __call($name, $arguments){
        if(is_callable([$this, $name])){
            return call_user_func_array([$this, $name], $arguments);
        }
    }
}


function PredefinedApp(){
    $app = new App('PredefinedApp', []);

    $app->cleanup = function($parent){
        // Do some stuff
    };
    return $app;
}

然后我创建一个这样的应用:

$app = new App('App1', ['PredefinedApp']);

它创建一个 App 实例，然后数组中的项目创建新的应用程序实例，无论其定义是什么，并将它们放入内部应用程序数组。

当我在主应用程序上执行我的析构函数时，它应该在所有子应用程序上调用 cleanup()。但正在发生的事情是，它正在执行一个无限循环，我不确定为什么。

我确实注意到，如果我注释掉 call_user_func_array 那么 __call() 只会被调用一次，但它不会执行实际的 closure 然后。

我还注意到，如果我在 __call() 中执行 var_dump()，它会无休止地转储。如果我在 cleanup() 中执行 var_dump() 而不是我得到一个 http 502 错误。

Answer 1

那么让我们通过代码看看这里发生了什么以及为什么:

01|    class App{ 
02|
03|        protected $apps = [];
04|
05|        public function __construct($name, $dependencies){
06|            $this->name = $name;
07|
08|            $apps = [];
09|            foreach($dependencies as $dependName){
10|                $apps[$name] = $dependName($this);
11|            }
12|            $this->apps = $apps;
13|        }
14|
15|        public function __destruct(){
16|            foreach($this->apps as $dep){
17|                $result = $dep->cleanup($this);
18|            }
19|        }
20|
21|        public function __call($name, $arguments){
22|            if(is_callable([$this, $name])){
23|                return call_user_func_array([$this, $name], $arguments);
24|            }
25|        }
26|    }
27|	
28|    function PredefinedApp(){
29|        $app = new App('PredefinedApp', []);
30|
31|        $app->cleanup = function($parent){
32|            //Do stuff like: echo "I'm saved";
33|        };
34|        return $app;
35|    }
36|		
37|    $app = new App('App1', ['PredefinedApp']);

_{注意:为代码的每一行添加了行号，因此我可以在下面的答案中引用这些行}

问题

1. 您使用以下行创建了一个实例:App:

   $app = new App('App1', ['PredefinedApp']);  //Line: 37

2. The constructor gets called:

   public function __construct($name, $dependencies){ /* Code here */ }  //Line: 05

   2.1. Following parameters are passed:

   • $name = "App1"
   • $dependencies = ["PredefinedApp"]

3. You assign $name to $this->name with this line:

   $this->name = $name;  //Line: 06

4. You initialize $apps with an empty array:

   $apps = [];  //Line: 08

5. Now you loop through each element of $dependencies, which has 1 element here (["PredefinedApp"])

6. In the loop you do the following:

   6.1 Assign the return value of a function call to an array index:

   $apps[$name] = $dependName($this);  //Line: 10
   //$apps["App1"] = PredefinedApp($this);

7. You call the function:

   PredefinedApp(){ /* Code here */}  //Line: 28

8. Now you create again a new instance of: App in PredefinedApp() same as before (Point 2 - 6, expect in the constructor you have other variable values + you don't enter the loop, since the array is empty)

9. You assign a closure to a class property:

   $app->cleanup = function($parent){  //Line: 31
       //Do stuff like: echo "I'm saved";
   };

10. You return the new created object of App:

    return $app;  //Line: 34

11. Here already the __destruct() gets called, because when the function ends the refcount goes to 0 of that zval and __destruct() is triggered. But since $this->apps is empty nothing happens here.

12. The new created object in that function gets returned and assigned to the array index (Note: We are back from the function to point 6.1):

    $apps[$name] = $dependName($this);  //Line: 10
    //$apps["App1"] = PredefinedApp($this);

13. The constructor ends with assigning the local array to the class property:

    $this->apps = $apps;  //Line: 12

14. Now the entire script ends (We have done line: 37)! Which means for the object $app the __destruct() is triggered for the same reason as before for $app in the function PredefinedApp()

15. Which means you now loop through each element from $this->apps, which only holds the returned object of the function:

    public function __destruct(){  //Line: 15
        foreach($this->apps as $dep){
            $result = $dep->cleanup($this);
        }
    }

    Array(
        "App1" => App Object
            (
                [apps:protected] => Array
                    (
                    )
    
                [name] => PredefinedApp
                [cleanup] => Closure Object
                    (
                        [parameter] => Array
                            (
                                [$parent] => <required>
                            )
    
                    )
    
            )
    )
    

16. 对于每个元素(这里只有 1 个)你执行:

    $result = $dep->cleanup($this);  //Line: 17

    But you don't call the closure! It tries to call a class method. So there is no cleanup class method, it's just a class property. Which then means __call() gets invoked:

    public function __call($name, $arguments){  //Line: 21
        if(is_callable([$this, $name])){
            return call_user_func_array([$this, $name], $arguments);
        }
    }

17. The $arguments contains itself ($this). And is_callable([$this, $name]) is TRUE, because cleanup is callable as closure.

18. So now we are getting in the endless stuff, because:

    return call_user_func_array([$this, $name], $arguments);  //Line: 23

    Is executed, which then looks something like this:

    return call_user_func_array([$this, "cleanup"], $this);

    Which then again tries to call cleanup as a method and again __call() is invoked and so on...

So at the end of the entire script the hole disaster starts. But I have some good news, as complicated this sounds, the solution is much simpler!

Solution

Just change:

return call_user_func_array([$this, $name], $arguments);  //Line: 23

with this:

return call_user_func_array($this->$name, $arguments);
                           //^^^^^^^^^^^ See here

因为像这样更改它，您不会尝试调用方法，而是调用闭包。所以如果你也把:

echo "I'm saved";

在闭包中分配它时，您将得到输出:

I'm saved