block本质

2 Replies

1、写一个简单的mac命令行程序，包含block定义与使用

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#import <Foundation/Foundation.h>
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        void (^block)(void) = ^{
            NSLog(@"Hello block!");
        };
        block();
    }
    return 0;
}

2、在命令行下编译成c++源文件xcrun -sdk iphoneos clang -arch arm64 -rewrite-objc main.m
3、得到的cpp文件有3万多行，找到尾部的main函数，与block相关的代码有：

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// 1、block定义，结构体__main_block_impl_0
struct __block_impl {
    void *isa;
    int Flags;
    int Reserved;
    void *FuncPtr;
};
struct __main_block_impl_0 {
    struct __block_impl impl;
    struct __main_block_desc_0* Desc;
    // 结构体构造函数
    __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;
    }
};
 
// 2.1、block体__main_block_func_0将做为参数传入block构造函数，__main_block_impl_0第一个参数
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
    // block内部代码
}
// 2.2、__main_block_impl_0构造函数第二个参数，__main_block_desc_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)};
 
/* 3、调用
 block = &__main_block_impl_0(__main_block_func_0, &__main_block_desc_0_DATA);
 block->FuncPtr(block);
 */
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);

4、总结：block本质是OC对象，block体等价于对象方法，在block体执行时会调用该方法；

2 thoughts on “block本质”

  1. Sian Post author

    1、block中如果涉及到参数，在生成block对象中，block体执行函数会增加相对应的参数传递

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    #import <Foundation/Foundation.h>
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        void (^block)(int,int) = ^(int a, int b){
            NSLog(@"Hello block!, a = %d, b = %d", a, b);
        };
        block(10, 20);
    }
    return 0;
}

    2、相关block对象中的执行函数

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    // 1、block定义
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;
  }
};
// 2、执行函数
static void __main_block_func_0(struct __main_block_impl_0 *__cself, int a, int b) {
 
            NSLog((NSString *)&__NSConstantStringImpl__var_folders_hv___lpn_vs5cg5s51kph0qmkx40000gn_T_main_8b75f1_mi_0, a, b);
        }
    ↓
  2. Sian Post author

    1、block中如果涉及到外部变量，在生成block对象时会新增相应的成员变量

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    struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int a;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _a, int flags=0) : a(_a) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};

    2、相对应的block结构体是这样的

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    int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int a = 10;
        void (^block)(void) = ^(){
            NSLog(@"Hello block!, a = %d", a);
        };
        block();
    }
    return 0;
}
    ↓

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