Block 原理

int main(int argc, char * argv[]) {
    @autoreleasepool {
        void (^block)(void) = ^{
            NSLog(@"Hello World!");
        };
        block();
        //return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}




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;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {

            NSLog((NSString *)&__NSConstantStringImpl__var_folders_5l_ypjn15q54cq9gp_xnd9wcvt40000gn_T_main_d00a24_mi_0);
        }

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)};


int main(int argc, char * argv[]) {
    /* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool; 
        void (*block)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));
        ((void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);

    }
}
static struct IMAGE_INFO { unsigned version; unsigned flag; } _OBJC_IMAGE_INFO = { 0, 2 };

一 、block 原理

block 定义：定义调用了block 的构造函数 __main_block_impl_0， 传参__main_block_func_0，将 __main_block_func_0 方法地址传给 block 的 FuncPtr，相当于 block 记录了方法指针。

block调用：直接调用 FuncPtr。

 

二、Block的几种形式

• 分为全局Block(_NSConcreteGlobalBlock)、栈Block(_NSConcreteStackBlock)、堆Block(_NSConcreteMallocBlock)三种形式

  其中栈Block存储在栈(stack)区，堆Block存储在堆(heap)区，全局Block存储在已初始化数据(.data)区

1、不使用外部变量的block是全局block

比如：

    NSLog(@"%@",[^{
        
    } class]);

输出：

__NSGlobalBlock__

2、使用外部变量并且未进行copy操作的block是栈block，copy 了是 堆block。

3、block 成员变量 默认拷贝到堆。