Scoped in webrtc_ refptr

        C++ The memory applied in the heap in requires the programmer to delete it manually , This is a C++ It is easy to cause the root cause of memory leakage . Have used Java All of our friends know ,Java There is a perfect memory recycling mechanism , There is no need for programmers to call the operation of freeing memory .C++ Is it possible to achieve something similar in Java The mechanism of automatically reclaiming memory ？ The answer is yes , and Webrtc Medium scoped_refptr Is to achieve similar functions .

         First, we start with the name of this class to understand its meaning . A name consists of three words , Respectively scope,ref,ptr.

         First look at ptr,C++ Programmers know this is pointer Pointer means , But the class name contains the semantics of pointers , How to understand this ？ The author is not just , Tell the truth , It took me a long time to figure out what happened . Let's start with the conclusion , stay webrtc in , All with ptr Ending class , If you create a non pointer object with this class , Can be used as the syntax of the pointer object . It is estimated that the readers are a little confused , The following is a practical example .
        Generally speaking ,C++ There are two ways to create objects , One is to create a pointer object .      

1. A *a = new A();

2. a->func(); 

         The other is to create non pointer objects ：

1. A a;

2. a.func（）

         Objects created by these two methods , The syntax of object calling methods is different . A is -> Way to call , A is . Way to call . But look ： 

1. scoped_refptr<A> temp;

2. temp->func();

                Have you noticed ？temp Is created as a non pointer , But it can use the syntax of the pointer object to call function methods . How is this realized ？ This is not difficult at all ,scoped_refptr In the code of operator-> The operator of . 

         T* operator->() const { return ptr_; }

            therefore , Like this ptr Ending class , It is best to create objects in a non pointer way . There is another advantage of creating objects in a non pointer way , When an object leaves its scope , It will automatically call the destructor of the object to destroy itself . This is also related to the following scope Words are related .

         To understand scope The meaning of , We need to learn a concept , It's called RAII. If you simply look at the full English name of this concept （Resouce Acquisition Is Initialization）, It will make people puzzling , I don't know . In fact, it is a pointer to the heap memory space , Stored in a stack space object , Through the stack space object automatic recycling function , At the same time, the method of reclaiming the heap memory pointed to by this pointer . Take a simple example , If we create a pointer object in a section of scope code , When leaving this scope , If the pointer is not passed to another method , At this point, you should explicitly call delete Release the pointer         

  1.A* a = new A();

      2.delete a;

       3.a = NULL;

           Although for experienced C++ For the programmer , The probability of forgetting to write the last two sentences is not high , But these large amounts of memory free code embedded in business code can not be ignored . So some people think of an advanced way to encapsulate the release of the pointer . Doing this ：        

   class scoped_A{undefined

        private :

        A *a;

       public:

        scoped_A(A* a){undefined

        this.a = a;

        }

        ~scoped_A(){undefined

        delete a;

        a = NULL;

        }

}
         The specific use ：

1. A* a = new A()

2. scoped_A(a) sa;

        perhaps ：

         scoped_A sa(new A());

            Did you see? ？ You can understand it as using a scoped_A The object of sa Put the pointer object a encase , When sa Automatically call when leaving the scope scoped_A Destructor of , To achieve automatic release a The purpose of the pointer . Have to say , This is a wonderful way . This is also scope The meaning of , It means this ptr Objects are scoped , Out of scope , Will automatically recycle .

            Finally, let's talk about ref,ref It means quoting . stay JAVA in , We often say that a piece of memory will be referenced by multiple variables , When this memory is not referenced by any variables , Memory will be recycled by garbage collection mechanism . stay C++ in , A piece of memory in the heap will also be referenced by multiple pointer variables at the same time （ Point to ）, Is there any way like JAVA equally , When this heap memory is not referenced by any pointer , What about automatic recycling ？ This is about Webrtc Medium RefCountedObject The class . An explanation of this class can be found in another article . To fully understand scoped_refptr, Need two articles to read together .
           summary ：scoped_refptr It is a realization in C++ Function class for automatically reclaiming object memory on . It can when the object leaves the scope , Judge whether to reclaim the memory in the heap by referring to the counter , Implemented the similarity Java The mechanism of garbage collection .