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Block系列3-block __block修饰符值捕获源码分析

Posted on Edited on In Disqus:

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int main(int argc, const char * argv[]) {
    @autoreleasepool {
        __block int age = 10;
        void(^block)(int, int) = ^(int a, int b){
            NSLog(@"This is block %d", age);
            NSLog(@"This is block %d", a);
            NSLog(@"This is block %d", b);
        };
        block(10, 12);
        
        age = 20;
    }
    return 0;
}

在加上__block以后，age的值被包装成了__Block_byref_age_0的对象，而且后续的访问也都是通过对象来访问里面的值

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//包装引用的外部参数
struct __Block_byref_age_0 {
  void *__isa;
__Block_byref_age_0 *__forwarding;
 int __flags;
 int __size;
 int age;
};

//Block实现类
struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  __Block_byref_age_0 *age; // by ref
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_age_0 *_age, int flags=0) : age(_age->__forwarding) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};

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

//最终Block中的代码分装
static void __main_block_func_0(struct __main_block_impl_0 *__cself, int a, int b) {
  __Block_byref_age_0 *age = __cself->age; // bound by ref

            NSLog((NSString *)&__NSConstantStringImpl__var_folders_kw_5dr8tfr96kn9f2mf2nh0111r0000gp_T_main_6d3256_mi_0, (age->__forwarding->age));
            NSLog((NSString *)&__NSConstantStringImpl__var_folders_kw_5dr8tfr96kn9f2mf2nh0111r0000gp_T_main_6d3256_mi_1, a);
            NSLog((NSString *)&__NSConstantStringImpl__var_folders_kw_5dr8tfr96kn9f2mf2nh0111r0000gp_T_main_6d3256_mi_2, b);
        }
        
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->age, (void*)src->age, 8/*BLOCK_FIELD_IS_BYREF*/);}

static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->age, 8/*BLOCK_FIELD_IS_BYREF*/);}

//Block描述信息
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};

//Main方法
int main(int argc, const char * argv[]) {
    /* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool; 
    
       //加上__block以后的外部参数age
        __attribute__((__blocks__(byref))) __Block_byref_age_0 age = {(void*)0,(__Block_byref_age_0 *)&age, 0, sizeof(__Block_byref_age_0), 10};
    
       //Block定义
        void(*block)(int, int) = ((void (*)(int, int))&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, (__Block_byref_age_0 *)&age, 570425344));
        
        //Block调用
        ((void (*)(__block_impl *, int, int))((__block_impl *)block)->FuncPtr)((__block_impl *)block, 10, 12);
        
        //后续age的访问
        (age.__forwarding->age) = 20;
    }
    return 0;
}