非ARC环境block类型

• __NSGlobalBlock__ - 没有访问auto变量 (访问的是static ,global或者没有访问变量)

//非ARC
      void(^block)(void) = ^{
          NSLog(@"hello");
      };    //__NSGlobalBlock__
   

• __NSStackBlock__ - 访问了auto变量

//非ARC
    int a = 10;
    
    void(^block)(void) = ^{
        NSLog(@"hello:%d",a);
    };  //__NSStackBlock__

• __NSMallocBlock__ - __NSStackBlock__调用了copy（__NSGlobalBlock__调用copy仍然是__NSGlobalBlock__）

//非ARC
    int a = 10;
    void(^block)(void) = [^{
        NSLog(@"hello:%d",a);
    } copy];    //__NSMallocBlock__

ARC环境block

ARC环境下编译器会根据以下情况将栈区block复制到堆区

• block作为返回值
• 使用强指针(__strong)指向block
• GCD函数中的block参数
• cocoa API中使用的usingBlock方法参数

property属性

• 非ARC
  @property(copy , nonatomic)void (^block)(void);

• ARC
  @property(strong , nonatomic)void (^block)(void);
  @property(copy , nonatomic)void (^block)(void);

对象类型的auto变量

• __NSStackBlock__无论是访问__strong还是__weak对象类型的auto变量,都不会强引用

• __NSMallocBlock__访问__strong对象类型的auto变量,会强引用;
  访问__weak修饰的对象类型auto变量，不会强引用

• block访问oc对象类型的auto变量会进行内存管理

static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->p, (void*)src->p, 3/*BLOCK_FIELD_IS_OBJECT*/);}

static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->p, 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};