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The bottom implementation of block

2022-07-18 16:32:00 【InfoQ】

Block The underlying implementation of

  • The original document ：

 int main(int argc, const char * argv[]) {
 ^{ };
 return 0;
 }

  • adopt clang The order will OC To C++ Code to check Block Underlying implementation ,clang The command is used by the terminal cd Locate the main.m File folder , And then use it clang -rewrite-objc main.m take OC To C++, After success main.m A... Will be generated in the same directory main.cpp file

 struct __block_impl {
 void *isa; //isa, A pointer to the class to which it belongs , That is to say block The type of
 int Flags; //flags, Flag variable , In the realization of block You'll use
 int Reserved; //Reserved, Keep variables
 void *FuncPtr; //block Pointer to the function called at execution time
 };

 struct __main_block_impl_0 {
 struct __block_impl impl;
 struct __main_block_desc_0* Desc;
 __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
 impl.isa = &_NSConcreteStackBlock; //__main_block_impl_0 Of isa The pointer points to _NSConcreteStackBlock
 impl.Flags = flags;
 impl.FuncPtr = fp; // from main Function , __main_block_impl_0 Of FuncPtr Points to the function __main_block_func_0
 Desc = desc; //__main_block_impl_0 Of Desc It also points to the definition __main_block_desc_0 It was created when __main_block_desc_0_DATA, Which records block Structure size and other information .
 }
 };

 static void __main_block_func_0(struct __main_block_impl_0 *__cself) {

 }

 static struct __main_block_desc_0 {
 size_t reserved; // Keep field
 size_t Block_size; //block size (sizeof(struct __main_block_impl_0))
 } __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
 // The above code defines __main_block_desc_0 When the structure is , At the same time, I created __main_block_desc_0_DATA, And assign it a value , For main Pair of functions __main_block_impl_0 To initialize .

 int main(int argc, const char * argv[]) {

 ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));

 return 0;
 }

  • __block_impl
    Structure , It contains  
    isa
    The pointer （ contain isa All pointers are objects ）, in other words  
    block
    It's also an object
  • __main_block_impl_0
    Structure , It can be seen that it is based on the function （main function ） And the occurrence sequence （ The first 0 individual ） Named , If it's global  
    blcok
    , It is named according to the variable name and occurrence sequence
  • __main_block_impl_0
    Contains two member variables and a constructor , The member variables are
    __block_impl
    Structure and description information
    Desc
    , Then initialize... In the constructor
    block
    Type information, function pointer and other information
  • __main_block_func_0
    function , In fact, it corresponds to
    block
    Function body , This function accepts a
    __cself
    Parameters , In fact, it's the corresponding
    block
    In itself
  • __main_block_desc_0
      Structure , The more valuable information is
    block
    Size
  • main
    Function pair
    block
    The creation of , You can see execution
    block
    Is to call a to
    block
    A function that is itself a parameter , This function corresponds to
    block
    The executive body of

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https://yzsam.com/2022/199/202207160946471823.html

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