ios block徹底理清之代碼分析

1.生成代碼抽取
block類型，默認爲0
// flags/_flags類型
enum {
/* See function implementation for a more complete description of these fields and combinations */
// 是一個對象
BLOCK_FIELD_IS_OBJECT = 3, /* id, NSObject, attribute((NSObject)), block, … */
// 是一個block
BLOCK_FIELD_IS_BLOCK = 7, /* a block variable */
// 被__block修飾的變量
BLOCK_FIELD_IS_BYREF = 8, /* the on stack structure holding the __block variable */
// 被__weak修飾的變量，只能被輔助copy函數使用
BLOCK_FIELD_IS_WEAK = 16, /* declared __weak, only used in byref copy helpers */
// block輔助函數調用（告訴內部實現不要進行retain或者copy）
BLOCK_BYREF_CALLER = 128 /* called from __block (byref) copy/dispose support routines. */
};

struct __block_impl {
  void *isa;//block類型指針
  int Flags;
  int Reserved;
  void *FuncPtr;//block函數指針
};


//block結構體，由構造函數傳入函數指針
struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int i;//block參數
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _i, int flags=0) : i(_i) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
//block函數體
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  int i = __cself->i; // bound by copy

  printf("i=%d", i);
 }

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
//使用
int main(){
    int i=1024;
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, i));
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);
    return 0;
}

2.理解
可以看出block的實質是實現一個結構體和一個函數指針
結構體中定義好block類型，和block參數，及函數指針地址
函數指針，實現訪問block結構體中的參數，並且對參數進行操作。

3.添加一些參數，再生成代碼

//源代碼
#include <stdio.h>
#ifdef __OBJC__
#import <Foundation/Foundation.h>
#endif

int main(){
    int i=1024;
    int j=3;
    NSString *str = @"hello";
    void (^blk)(void) = ^{
        printf("i=%d,j=%d", i,j);
        NSLog(str);
    };

    blk();
    return 0;
}

//生成代碼抽取

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int i;
  int j;
  NSString *str;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _i, int _j, NSString *_str, int flags=0) : i(_i), j(_j), str(_str) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  int i = __cself->i; // bound by copy
  int j = __cself->j; // bound by copy
  NSString *str = __cself->str; // bound by copy

  printf("i=%d,j=%d", i,j);
        NSLog(str);
 }
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->str, (void*)src->str, 3/*BLOCK_FIELD_IS_OBJECT*/);}

static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->str, 3/*BLOCK_FIELD_IS_OBJECT*/);}

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
  void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
  void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(){
 int i=1024;
    int j=3;
    NSString *str = (NSString *)&__NSConstantStringImpl__var_folders_bf_l6g0_cmn1n7bpy8415kcc6dr0000gq_T_2_d864aa_i_0;
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, i, j, str, 570425344));

 ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);
 return 0;
}

4.好的參考
tripleCC-Block技巧與底層解析
block內存管理-文件夾_IOS
block內存講解
block內存泄露深入分析這裏寫鏈接內容