Block bottom Implementation Disassembly

In many of the system methods are used in the block, its essence is the function pointer Void (*block) ()

often use block instead of proxy

In C, the function is the address entry that holds the entire function, calling function execution directly.

and block, just call a piece of code, execute at the right time.

Demo:

int a = 10;          __block int b = 20;           void  (^block) ()  = ^ () {                            printf ("a = %d\n", a);                            printf ("b = %d\n ", b);                    };         a = 50;          b = 30;             block (); 

CLANG-REWRITE-OBJC main.m

Int main (int argc, const char * argv[])  {         int a = 10;        //__block-Modified, encapsulated in a structural body __BLOCK_BYREF_B_0        __ATTRIBUTE__ ((__blocks__ (ByRef)))  __ block_byref_b_0 b = {(void*) 0, (__block_byref_b_0 *) &b, 0, sizeof (__Block_ BYREF_B_0),  20};        //is passed into the struct STRUCT __MAIN_BLOCK_IMPL_0   __main_block_impl_0 (...) {...}         void  (*block) ()  =  (void (*) ()) &__main_block _impl_0 (void *) __main_block_func_0, &__main_block_desc_0_data, a,  (__Block_byref_b_0  *) &b, 570425344);        a = 50;         //Structure property value re-points to          (b. __forwarding->b)  = 30;        //gets the struct property funcptr. That is, the encapsulated block method body. Then pass in the block instance, perform print          ((void  (*) (__block_impl *)) ((__block _impl *) (block)->funcptr) ((__block_impl *) block);                         return 0;     }

--------------Disassembly:

A>

__ATTRIBUTE__ ((__blocks__ (ByRef))) __block_byref_b_0 B = {(void*) 0, (__BLOCK_BYREF_B_0 *) &b, 0, sizeof (__block_ BYREF_B_0), 20};

Parameter: (void*)0

< Span style= "Color:rgb (147, 161, 161); Font-family:consolas, ' Liberation Mono ', Menlo, Courier, monospace; font-size:13px; line-height:18px; White-space:pre; Background-color:rgb (247, 247, 249); " >         ( __block_byref_b_0 b

< Span style= "Color:rgb (147, 161, 161); Font-family:consolas, ' Liberation Mono ', Menlo, Courier, monospace; font-size:13px; line-height:18px; White-space:pre; Background-color:rgb (247, 247, 249); " >         0

< Span style= "Color:rgb (147, 161, 161); Font-family:consolas, ' Liberation Mono ', Menlo, Courier, monospace; font-size:13px; line-height:18px; White-space:pre; Background-color:rgb (247, 247, 249); " >          __block_byref_b_0)

20

< Span style= "Color:rgb (147, 161, 161); Font-family:consolas, ' Liberation Mono ', Menlo, Courier, monospace; font-size:12px; " > encapsulate the value of B to __BLOCK_BYREF_B_0 the structure of the body. "Encapsulated structure for __block decorated values"

struct __block_byref_b_0 {void *__isa;//Current object pointer __block_byref_b_0 *__forwarding;//current struct pointer, __forwarding stored from Your own address. Execute int __flags with __block decoration; Mark int __size; struct size int b; Value};

B> passed to the method in the struct body

void (*block) () = (void (*) ()) &__main_block_impl_0 ((void *) __main_block_func_0, &__main_block_desc_0_data, A, (__BLOCK_BYREF_B_0 *) &b, 570425344);

Passed:(void *)__main_block_func_0//Storage block Method Body "is here two print", the following *FP

           & __main_block_desc_0_data  //  Address, block description data

A//value transfer

(__block_byref_b_0*) &bPass the address of B, structure wrapper

570425344

< Span style= "Color:rgb (25, 95, 145); Font-family:consolas, ' Liberation Mono ', Menlo, Courier, monospace; font-size:12px; " > to: Instance method of block

Struct __main_block_impl_0 {        struct __block_impl  impl;        struct __main_block_desc_0* Desc;         int a; //  10         __Block_byref_b_0 *b; // by ref                 //call this method, the implementation of the method is within parentheses. The parameters passed above are assigned here          __main_block_impl_0 (void *fp, struct __main_block_desc_0 * desc, int _a, __block_byref_b_0 *_b, int flags=0)  : a (_a),  b (_b- >__forwarding)  {            impl.isa  = &_nsconcretestackblock;            impl . Flags = flags;&nBsp;           impl. Code   print performed by funcptr = fp;  //. __main_block_func_0            desc =  desc;        }    }

The methods inside the block are encapsulated here.

static void __main_block_func_0 (struct  __main_block_impl_0 *__cself)  {      __block_byref_b_0 *b  = __cself->b; // bound by ref      int a  = __cself->a; // bound by copy         printf ("a = %d\n", a);         printf ("b = %d\ N ", (b->__forwarding->b));     } 

struct __block_impl {void *isa;               int Flags;               int Reserved;         void *funcptr; };

C>

A = 50; (b.__forwarding->b) = 30;

The b here is __block_byref_b_0 b .

Gets the attribute __forwarding in the struct and points it to the value 30;

Use __block and do not use. Always a pass, one is a value.

After being compiled into C + +, it is found that when __block decorated objects are used, they are encapsulated into one type of struct.

Block bottom Implementation Disassembly