- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSLog(@"1111");
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"2222");
    });
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    dispatch_queue_t queue1 = dispatch_queue_create("com.apple.queue1", DISPATCH_QUEUE_SERIAL);
    NSLog(@"start");
    dispatch_async(queue1, ^{
        sleep(5);
        NSLog(@"1 -- %@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue1, ^{
        sleep(5);
        NSLog(@"2 -- %@",[NSThread currentThread]);
    });
    sleep(5);
    NSLog(@"finished");
 }

DISPATCH_DECL(dispatch_queue_attr);

#define DISPATCH_DECL(name) typedef struct name##_s *name##_t;

#define DISPATCH_VTABLE_HEADER(x)	\
	unsigned long const do_type;	\
	const char *const do_kind; \
	size_t (*const do_debug)(struct x *, char *, size_t);	\
	struct dispatch_queue_s *(*const do_invoke)(struct x *);	\
	bool (*const do_probe)(struct x *); \
	void (*const do_dispose)(struct x *)
	
	
#define DISPATCH_STRUCT_HEADER(x, y)	\
	const struct y *do_vtable;	\
	struct x *volatile do_next;	\
	unsigned int do_ref_cnt;	\
	unsigned int do_xref_cnt;    \
	unsigned int do_suspend_cnt;	\
	struct dispatch_queue_s *do_targetq;	\
	void *do_ctxt; \
	void *do_finalizer
	
	
#define DISPATCH_QUEUE_MIN_LABEL_SIZE 64

#ifdef __LP64__
#define DISPATCH_QUEUE_CACHELINE_PAD 32
#else
#define DISPATCH_QUEUE_CACHELINE_PAD 8
#endif

	
struct dispatch_object_vtable_s {
	DISPATCH_VTABLE_HEADER(dispatch_object_s);
};

//将宏展开
struct dispatch_object_vtable_s {
	unsigned long const do_type;
	const char *const do_kind;
	size_t (*const do_debug)(struct dispatch_object_s *, char *, size_t);
	struct dispatch_queue_s *(*const do_invoke)(struct x *);
	bool (*const do_probe)(struct dispatch_object_s *);
	void (*const do_dispose)(struct dispatch_object_s *)
};



struct dispatch_object_s {
	DISPATCH_STRUCT_HEADER(dispatch_object_s, dispatch_object_vtable_s);
};

//将宏展开
struct dispatch_object_s {
	const struct dispatch_object_vtable_s *do_vtable;
	struct dispatch_object_s *volatile do_next;
	unsigned int do_ref_cnt;
	unsigned int do_xref_cnt;
	unsigned int do_suspend_cnt;
	struct dispatch_queue_s *do_targetq;
	void *do_ctxt;
	void *do_finalizer;
};



#define DISPATCH_QUEUE_HEADER \
	uint32_t volatile dq_running; \
	uint32_t dq_width; \
	struct dispatch_object_s *volatile dq_items_tail; \
	struct dispatch_object_s *volatile dq_items_head; \
	unsigned long dq_serialnum; \
	dispatch_queue_t dq_specific_q;	
	
	
	

struct dispatch_queue_s {
	DISPATCH_STRUCT_HEADER(dispatch_queue_s, dispatch_queue_vtable_s);
	DISPATCH_QUEUE_HEADER;
	char dq_label[DISPATCH_QUEUE_MIN_LABEL_SIZE]; // must be last
	char _dq_pad[DISPATCH_QUEUE_CACHELINE_PAD]; // for static queues only
};

//将宏展开

struct dispatch_queue_s {
	const struct dispatch_queue_vtable_s *do_vtable;
	struct dispatch_queue_s *volatile do_next;
	unsigned int do_ref_cnt;
	unsigned int do_xref_cnt;
	unsigned int do_suspend_cnt;
	struct dispatch_queue_s *do_targetq;
	void *do_ctxt;
	void *do_finalizer;
	
	uint32_t volatile dq_running;
	uint32_t dq_width;
	struct dispatch_object_s *volatile dq_items_tail;
	struct dispatch_object_s *volatile dq_items_head;
	unsigned long dq_serialnum; 
	dispatch_queue_t dq_specific_q;
	
	char dq_label[DISPATCH_QUEUE_MIN_LABEL_SIZE]; // must be last
	char _dq_pad[DISPATCH_QUEUE_CACHELINE_PAD]; // for static queues only
};






	
struct dispatch_queue_attr_vtable_s {
	DISPATCH_VTABLE_HEADER(dispatch_queue_attr_s);
};

struct dispatch_queue_attr_s {
	DISPATCH_STRUCT_HEADER(dispatch_queue_attr_s, dispatch_queue_attr_vtable_s);

	// Public:
	int qa_priority;
	void* finalizer_ctxt;
	dispatch_queue_finalizer_function_t finalizer_func;

	// Private:
	unsigned long qa_flags;
};


//宏影响阅读，将其展开

struct dispatch_queue_attr_vtable_s {
	unsigned long const do_type;	
	const char *const do_kind; 
	size_t (*const do_debug)(struct dispatch_queue_s *, char *, size_t);	
	struct dispatch_queue_s *(*const do_invoke)(struct dispatch_queue_s *);	
	bool (*const do_probe)(struct dispatch_queue_s *); 
	void (*const do_dispose)(struct dispatch_queue_s *);
};


struct dispatch_queue_attr_s {
	const struct dispatch_queue_attr_vtable_s *do_vtable;
	struct dispatch_queue_attr_s *volatile do_next;
	unsigned int do_ref_cnt;
	unsigned int do_xref_cnt;
	unsigned int do_suspend_cnt;
	struct dispatch_queue_s *do_targetq;
	void *do_ctxt;
	void *do_finalizer;
	
	// Public:
	int qa_priority;
	void* finalizer_ctxt;
	dispatch_queue_finalizer_function_t finalizer_func;

	// Private:
	unsigned long qa_flags;
};