Block原理探究(上篇)-Block本质及存储域问题

//main.m文件：
#import <Foundation/Foundation.h>
int main(int argc, char * argv[]) {
    int num = 10;
    void (^myBlock)(void) =^{NSLog(@"num = %d",num);};
    myBlock();
    return 0;
}

clang -rewrite-objc 源代码文件名(如此例中的main.m)

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

static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  int num = __cself->num; // bound by copy
NSLog((NSString *)&__NSConstantStringImpl__var_folders_wd_fhcn9bn91v56nlzv9mt5z8ym0000gn_T_main_9e3646_mi_0,num);}

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[]) {
    int num = 10;
    void (*myBlock)(void) =((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, num));
    ((void (*)(__block_impl *))((__block_impl *)myBlock)->FuncPtr)((__block_impl *)myBlock);
    return 0;
}

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

impl.isa = &_NSConcreteStackBlock;

- (void)testBlock5 {
    void(^block)(int a) = ^(int a) {
        NSLog(@"This is a block");
    };
    
    NSLog(@"%@",[block class]);
    NSLog(@"%@",[[block class] superclass]);
    NSLog(@"%@",[[[block class] superclass] superclass]);
    NSLog(@"%@",[[[[block class] superclass] superclass] superclass]);
}

//打印结果：
//__NSGlobalBlock__
//__NSGlobalBlock
//NSBlock
//NSObject

- (void)testBlock7 {
    //1.Block内部没有调用外部自动变量
    void (^block1)(void) = ^{
        NSLog(@"Block");
    };
    
    //2.Block内部调用外部自动变量
    int a = 10;
    void (^block2)(void) = ^{
        NSLog(@"Block-%d",a);
    };
    
    //3.拷贝栈上的block
    void (^block3)(void) = ^{
        NSLog(@"Block-%d",a);
    };
    
    //打印Block类型
    NSLog(@"%@ %@ %@", [block1 class], [block2 class], [[block3 copy] class]);
}

//打印结果：
//__NSGlobalBlock__ __NSStackBlock__ __NSMallocBlock__

typedef void(^PrintBlock)(void);

@interface ViewController ()
@property (nonatomic ,copy)PrintBlock block1;
@property (nonatomic ,copy)PrintBlock block2;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self createBlock];
    self.block1();
    self.block2();
    NSLog(@"block1:%@", [self.block1 class]); //报错Thread 1: EXC_BAD_ACCESS (code=1, address=0x7ffeeb90b8c0)
    NSLog(@"block2:%@", [self.block2 class]);
}

- (void)createBlock {
    int a = 10;
    //此处采用直接赋值的方式，不会触发setter方法
    _block1 = ^{
        NSLog(@"This is block1-%d",a);
    };
    
    self.block2 = ^{
        NSLog(@"This is block2-%d",a);
    };
    //离开此作用域，block1就会被释放
    NSLog(@"block1:%@、block2:%@", [self.block1 class],[self.block2 class]);
}
@end

block1:__NSStackBlock__、block2:__NSMallocBlock__
This is block1-10
This is block2-10

typedef void(^Block)(void);
-(Block)getBlock{
    //ARC下的Block中访问了auto变量，此时block类型应为__NSStackBlock__
   int a = 10;
   return  ^{
        NSLog(@"---------%d", a);
    };
}

- (void)testBlock9 {
    //1.测试block作为函数返回值时
    NSLog(@"bock1-：%@",[[self getBlock] class]);
    
    //2.测试将block赋值给__strong指针时
    int a = 10;
    
    //2.1.block内没有访问auto变量
    Block block21 = ^{
        NSLog(@"block21");
    };
    NSLog(@"block21-%@",[block21 class]);
    
    //2.2.block内访问了auto变量，但没有赋值给__strong指针
    NSLog(@"block22-%@",[^{
        NSLog(@"block22-%d", a);
    } class]);

    //2.3.block赋值给__strong指针
    Block block23 = ^{
        NSLog(@"block23");
    };
    NSLog(@"block23-%@",[block23 class]);
    
    //3.block作为Cocoa API中方法名含有usingBlock的方法参数时
    NSArray *array = @[@"1",@"2",@"3"];
    [array enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        
    }];
    
    //4.block作为GCD API的方法参数时
    //Block中的延时操作完成时，系统将会对Block进行释放
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        
    });
}

//打印结果如下:
//bock1-：__NSMallocBlock__
//block21-__NSGlobalBlock__
//block22-__NSStackBlock__
//block23-__NSGlobalBlock__

//MRC下block属性的建议写法：
@property (copy, nonatomic) void (^block)(void);

//ARC下block属性的建议写法：
@property (strong, nonatomic) void (^block)(void);
@property (copy, nonatomic) void (^block)(void);