1 OS_object
OS_object由下面宏OS_OBJECT_DEC_BASE扩展而来:
// 1. os/object.h OS_OBJECT_DECL_BASE(object, NSObject); // 2. os/object.h #define OS_OBJECT_DECL_BASE(name, ...) @interface OS_OBJECT_CLASS(name) : __VA_ARGS__ - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end 扩展之后的结果为:
@interface OS_object : NSObject - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end 从扩展的结果来看，OS_object继承自NSObject。
OS_object实现部分位于 src/object.m 中:
@implementation OS_OBJECT_CLASS(object) DISPATCH_UNAVAILABLE_INIT() -(id)retain { return _os_object_retain(self); } -(oneway void)release { return _os_object_release_without_xref_dispose(self); } -(NSUInteger)retainCount { return _os_object_retain_count(self); } #pragma clang diagnostic push #pragma clang diagnostic ignored "-Wdeprecated-implementations" -(BOOL)retainWeakReference { return _os_object_retain_weak(self); } -(BOOL)allowsWeakReference { return _os_object_allows_weak_reference(self); } #pragma clang diagnostic pop - (void)_xref_dispose { return _os_object_release_internal(self); } @end 宏OS_OBJECT_CLASS的作用就是给宏参数加一个OS_前缀，因此OS_OBJECT_CLASS(object)扩展之后就是OS_object。
GCD 源码为OS_object定义了一个指针类型:
// 1. os/object_private.h typedef OS_OBJECT_CLASS(object) *_os_object_t; 上面代码中将宏扩展开，就是做了如下定义:
typdef OS_object *_os_object_t; 2 OS_dispatch_object
OS_dispatch_object由宏OS_OBJECT_DECL_CLASS扩展而来:
// 1. dispatch/object.h OS_OBJECT_DECL_CLASS(dispatch_object); // 2. os/object.h #define OS_OBJECT_DECL_CLASS(name) OS_OBJECT_DECL_SUBCLASS_SWIFT(name, object) // 3. os/object.h #define OS_OBJECT_DECL_SUBCLASS_SWIFT(name, super) OS_EXPORT OS_OBJECT_OBJC_RUNTIME_VISIBLE OS_OBJECT_DECL_IMPL_CLASS(name, OS_OBJECT_CLASS(super)) // 4. os/object.h #define OS_OBJECT_DECL_IMPL_CLASS(name, ...) OS_OBJECT_DECL_BASE(name, ## __VA_ARGS__) typedef OS_OBJECT_CLASS(name) * OS_OBJC_INDEPENDENT_CLASS name##_t 扩展之后的结果为:
@interface OS_dispatch_object : OS_object - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_object *dispatch_object_t 从扩展结果看，OS_dispatch_object继承自OS_object。
上面注释 3 处的宏OS_OBJECT_OBJC_RUNTIME_VISIBLE 和注释 4 处的宏OS_OBJC_INDEPENDENT_CLASS都是 Clang 编译器的属性，对数据结构本身没有影响，因此没有写出来。比如宏OS_OBJECT_OBJC_RUNTIME_VISIBLE扩展之后就是:
__attribute__((objc_runtime_visible)) OS_dispatch_object的实现位于 src/object.m 中:
@implementation DISPATCH_CLASS(object) DISPATCH_UNAVAILABLE_INIT() - (NSString *)debugDescription { Class nsstring = objc_lookUpClass("NSString"); if (!nsstring) return nil; char buf[2048]; struct dispatch_object_s *obj = (struct dispatch_object_s *)self; if (dx_vtable(obj)->do_debug) { dx_debug(obj, buf, sizeof(buf)); } else { strlcpy(buf, object_getClassName(self), sizeof(buf)); } NSString *format = [nsstring stringWithUTF8String:"<%s: %s>"]; if (!format) return nil; return [nsstring stringWithFormat:format, object_getClassName(self), buf]; } #pragma clang diagnostic push #pragma clang diagnostic ignored "-Wobjc-missing-super-calls" - (void)dealloc { return _dispatch_dispose(self); } #pragma clang diagnostic pop @end 宏DISPATCH_CLASS的作用是在宏参数前面加上前缀OS_dispatch_，因此DISPATCH_CLASS(object)扩展之后就是OS_dispatch_object。
3 OS_dispatch_queue
OS_dispatch_queue由宏DISPATCH_DECL_FACTORY_CLASS_SWIFT扩展而来:
// 1. dispatch/queue.h DISPATCH_DECL_FACTORY_CLASS_SWIFT(dispatch_queue, DispatchQueue); // 2. dispatch/object.h #define DISPATCH_DECL_FACTORY_CLASS_SWIFT(name, swift_name) OS_OBJECT_SWIFT_HAS_MISSING_DESIGNATED_INIT DISPATCH_DECL_SWIFT(name, swift_name) // 3. dispatch/object.h #define DISPATCH_DECL_SWIFT(name, swift_name) DISPATCH_SWIFT_NAME(swift_name) DISPATCH_DECL(name) // 4. dispatch/object.h #define DISPATCH_DECL(name) OS_OBJECT_DECL_SENDABLE_SUBCLASS_SWIFT(name, dispatch_object) // 5. os/object.h #define OS_OBJECT_DECL_SENDABLE_SUBCLASS_SWIFT(name, super) OS_EXPORT OS_OBJECT_OBJC_RUNTIME_VISIBLE OS_OBJECT_SWIFT_SENDABLE OS_OBJECT_DECL_IMPL_CLASS(name, OS_OBJECT_CLASS(super)) 扩展之后的结果为:
@interface OS_dispatch_queue : OS_dispatch_object - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_queue *dispatch_queue_t; 从扩展结果看OS_dispatch_queue继承自OS_dispatch_object。
OS_dispatch_queue的实现部分位于 src/object.m 中:
@implementation DISPATCH_CLASS(queue) OS_OBJECT_NONLAZY_CLASS_LOAD DISPATCH_UNAVAILABLE_INIT() DISPATCH_OBJECT_USES_XREF_DISPOSE() - (NSString *)description { Class nsstring = objc_lookUpClass("NSString"); if (!nsstring) return nil; NSString *format = [nsstring stringWithUTF8String:"<%s: %s>"]; if (!format) return nil; return [nsstring stringWithFormat:format, object_getClassName(self), dispatch_queue_get_label(self), self]; } - (void)_xref_dispose { _dispatch_queue_xref_dispose((struct dispatch_queue_s *)self); [super _xref_dispose]; } @end 宏DISPATCH_CLASS(queue)扩展之后就是OS_dispatch_queue。
4 OS_dispatch_queue_serial
OS_dispatch_queue_serial由宏DISPATCH_DECL_SERIAL_EXECUTOR_SWIFT扩展而来:
// 1. dispatch/queue.h DISPATCH_DECL_SERIAL_EXECUTOR_SWIFT(dispatch_queue_serial, DispatchSerialQueue); // 2. dispatch/object.h #define DISPATCH_DECL_SERIAL_EXECUTOR_SWIFT(name, swift_name) DISPATCH_DECL_SUBCLASS_SWIFT(name, dispatch_queue, swift_name) // 3. dispatch/object.h #define DISPATCH_DECL_SUBCLASS_SWIFT(name, base, swift_name) DISPATCH_SWIFT_NAME(swift_name) DISPATCH_DECL_SUBCLASS(name, base) // 4. dispatch/object.h #define DISPATCH_DECL_SUBCLASS(name, base) OS_OBJECT_DECL_SENDABLE_SUBCLASS_SWIFT(name, base) 扩展之后的结果为:
@interface OS_dispatch_queue_serial : OS_dispatch_queue - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_queue_searial *dispatch_queue_searial_t; 从扩展结果看，OS_dispatch_queue_serial继承自OS_dispatch_queue。
OS_dispatch_queue_serial的实现位于 src/object.m 中:
// 1. src/object.m DISPATCH_CLASS_IMPL(queue_serial) // 2. src/object.m #define DISPATCH_CLASS_IMPL(name) EMPTY_OS_OBJECT_CLASS_IMPL(DISPATCH_CLASS(name)) // 3. src/object.m #define EMPTY_OS_OBJECT_CLASS_IMPL(name) OS_OBJECT_NONLAZY_CLASS @implementation name OS_OBJECT_NONLAZY_CLASS_LOAD DISPATCH_UNAVAILABLE_INIT() @end // 4. src/object_internal.h #define DISPATCH_UNAVAILABLE_INIT() - (instancetype)init { DISPATCH_CLIENT_CRASH(0, "-init called directly"); return [super init]; } 扩展之后的结果为:
@implementation OS_dispatch_queue_serial - (instancetype)init { return [super init]; } @end 5 OS_dispatch_queue_concurrent
OS_dispatch_queque_concurrent由宏DISPATCH_DECL_SUBCLASS_SWIFT扩展而来:
// 1. dispatch/queue.h DISPATCH_DECL_SUBCLASS_SWIFT(dispatch_queue_concurrent, dispatch_queue, DispatchConcurrentQueue); 扩展结果为:
@interface OS_dispatch_queue_concurrent : OS_dispatch_queue - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_queue_concurrent *dispatch_queue_concurrent_t; 从扩展结果看，OS_dispatch_queue_concurrent继承自OS_dispatch_queue。
OS_dispatch_queue_concurrent的实现位于 src/object.m 中:
DISPATCH_CLASS_IMPL(queue_concurrent) 扩展之后的结果为:
@implementation OS_dispatch_queue_concurrent - (instancetype)init { return [super init]; } @end 5 OS_dispatch_queue_main
OS_dispatch_queue_main由宏DISPATCH_DECL_SUBCLASS扩展而来:
// 1. dispatch/queue.h DISPATCH_DECL_SUBCLASS(dispatch_queue_main, dispatch_queue_serial); 扩展的结果为:
@interface OS_dispatch_queue_main : OS_dispatch_queue_serial - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_queue_main *dispatch_queue_main_t; 从扩展结果看，OS_dispatch_queue_main继承自OS_dispatch_queue_serial。
OS_dispatch_queue_main的实现部分位于 src/object.m 中:
// 1. src/object.m DISPATCH_CLASS_IMPL(queue_main) 扩展之后的结果为:
@implementation OS_dispatch_queue_main - (instancetype)init { return [super init]; } @end 6 OS_dispatch_queue_global
OS_disaptch_queue_global由宏DISPATCH_DECL_SUBCLASS扩展而来:
// 1. dispatch/queue.h DISPATCH_DECL_SUBCLASS(dispatch_queue_global, dispatch_queue); 扩展之后的结果为:
@interface OS_dispatch_queue_global : OS_dispatch_queue - (instancetype)init OS_SWIFT_UNAVAILABLE("Unavailable in Swift"); @end typedef OS_dispatch_queue_global *dispatch_queue_global_t; 从扩展结果看，OS_dispatch_queue_global继承自OS_dispatch_queue。
OS_dispatch_queue_global的实现位于 src/object.m 中:
// 1. src/object.m DISPATCH_CLASS_IMPL(queue_global) 扩展结果之后为:
@implementation OS_dispatch_queue_global - (instancetype)init { return [super init]; } @end 2 OC 协议
2.1 <OS_object>
<OS_object>由宏OS_OBJECT_DECL_PROTOCOL定义:
// 1. os/object_private.h OS_OBJECT_DECL_PROTOCOL(object, <NSObject>); // 2. os/object.h #define OS_OBJECT_DECL_PROTOCOL(name, ...) @protocol OS_OBJECT_CLASS(name) __VA_ARGS__ @end 宏扩展的结果为:
@protocol OS_object <NSObject> @end 从扩展结果可以知道，<OS_object>继承自<NSObject>。
2.2 <OS_dispatch_object>
<OS_dispatch_object>由宏_OS_OBJECT_DECL_PROTOCOL定义:
// 1. src/object_internal.h _OS_OBJECT_DECL_PROTOCOL(dispatch_object, object); // 2. os/object_private.h #define _OS_OBJECT_DECL_PROTOCOL(name, super) OS_OBJECT_DECL_PROTOCOL(name, <OS_OBJECT_CLASS(super)>) 宏扩展之后的结果为:
@protocol OS_dispatch_object <OS_object> @end 从扩展结果可以看出，<OS_dispatch_object>继承自<OS_object>。
2.3 <OS_dispatch_queue>
<OS_dispatch_queue>由宏DISPATCH_CLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_CLASS_DECL(queue, QUEUE); // 2. src/object_internal.h #define DISPATCH_CLASS_DECL(name, cluster) _OS_OBJECT_DECL_PROTOCOL(dispatch_##name, dispatch_object) _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(dispatch_##name, dispatch_##name) DISPATCH_CLASS_DECL_BARE(name, cluster) 宏DISPATCH_CLASS_DECL有 3 个宏构成，其中宏DISPATCH_CLASS_DECL_BARE后面再说。
宏_OS_OBJECT_DECL_PROTOCOL扩展之后的结果为:
@protocol OS_dispatch_queue <OS_dispatch_object> @end 从扩展结果看，<OS_dispatch_queue>继承自<OS_dispatch_object>。
宏_OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL的定义如下:
// 1. os/object_private.h #define _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(name, super) OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(name, super) // 2. os/object.h #define OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(name, proto) OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL_IMPL( OS_OBJECT_CLASS(name), OS_OBJECT_CLASS(proto)) // 3. os/object.h #define OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL_IMPL(name, proto) @interface name () <proto> @end 宏的扩展结果为:
@interface OS_dispatch_queue () <OS_dispatch_queue> @end 从扩展结果可知，OS_dispatch_queue实现了同名协议<OS_dispatch_queue>。
2.4 <OS_dispatch_queue_serial>
<OS_dispatch_queue_serial>由宏DISPATCH_SUBCLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_serial, queue_serial_executor, lane); // 2. src/object_internal.h #define DISPATCH_SUBCLASS_DECL(name, super, ctype) _OS_OBJECT_DECL_PROTOCOL(dispatch_##name, dispatch_##super); _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(dispatch_##name, dispatch_##name) OS_OBJECT_SUBCLASS_DECL(dispatch_##name, dispatch_##ctype) 宏DISPATCH_SUBCLASS_DECL由 3 个宏构成，其中宏OS_OBJECT_SUBCLASS_DECL后面再说。
宏_OS_OBJECT_DECL_PROTOCOL _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL扩展的结果为:
@protocol OS_dispatch_queue_serial <OS_dispatch_queue_serial_executor> @end @interface OS_dispatch_queue_serial () <OS_dispatch_queue_serial> @end 从扩展结果可以知道，<OS_dispatch_queue_serial>继承自<OS_dispatch_queue_serial_executor>。同时，OS_dispatch_queue_serial实现了同名协议<OS_dispatch_queue_serial>。
协议<OS_dispatch_queue_serial_executor>是 GCD 内部的一个协议，同样也有宏DISPATCH_SUBCLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_serial_executor, queue, lane); 因此，协议<OS_dispatch_queue_serial_executor>继承自<OS_dispatch_queue>`。
2.5 <OS_dispatch_queue_concurrent>
<OS_dispatch_queue_concurrent>由宏DISPATCH_SUBCLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_concurrent, queue, lane); 宏扩展的结果为:
@protocol OS_dispatch_queue_concurrent <OS_dispatch_queue> @end @interface OS_dispatch_queue_concurrent () <OS_dispatch_queue_concurrent> @end 从扩展结果可以知道，<OS_dispatch_queue_concurrent>继承自<OS_dispatch_queue>。同时，OS_dispatch_queue_concurrent实现了同名的<OS_dispatch_queue_concurrent>。
2.6 <OS_dispatch_queue_main>
OS_dispatch_queue_main由宏DISPATCH_SUBCLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_main, queue_serial, lane); 宏扩展结果为：
@protocol OS_dispatch_queue_main <OS_dispatch_queue_serial> @end @interface OS_dispatch_queue_main () <OS_dispatch_queue_main> @end 从扩展结果可以知道，<OS_dispatch_queue_main>继承自<OS_dispatch_queue_serial>。同时，OS_dispatch_queue_main实现了同名的<OS_dispatch_queue_main>。
2.7 <OS_dispatch_queue_global>
<OS_dispatch_queue_global>由宏DISPATCH_SUBCLASS_DECL`定义:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_global, queue, lane); 宏扩展的结果为:
@protocol OS_disaptch_queue_global <OS_dispatch_queue> @end @interface OS_dispatch_queue_global () <OS_dispatch_queue_global> @end 从扩展结果可以知道，<OS_dispatch_queue_global>继承自<OS_dispatch_queue>。同时，OS_dispatch_queue_global实现了同名协议<OS_dispatch_queue_global>。
3 Struct
3.1 _os_object_s 与 _os_object_vtable_s
_os_object_s定义如下:
// 1. src/object_internal.h typedef struct _os_object_s { _OS_OBJECT_HEADER( const _os_object_vtable_s *__ptrauth_objc_isa_pointer os_obj_isa, os_obj_ref_cnt, os_obj_xref_cnt); } _os_object_s; 宏_OS_OBJECT_HEADER定义如下:
// 1. os/object_private.h #define _OS_OBJECT_HEADER(isa, ref_cnt, xref_cnt) isa; /* must be pointer-sized and use __ptrauth_objc_isa_pointer */ int volatile ref_cnt; int volatile xref_cnt 因此，_os_object_s完整的定义如下:
typedef struct _os_object_s { const _os_object_vtable_s *__ptrauth_objc_isa_pointer os_obj_isa, int volatile os_obj_ref_cnt; int volatile os_obj_xref_cnt; } _os_object_s; _os_object_vtable_s的定义如下:
// 1. src/object_internal.h typedef struct _os_object_vtable_s { _OS_OBJECT_CLASS_HEADER(); } _os_object_vtable_s; 宏_OS_OBJECT_CLASS_HEADER定义如下:
// 1. os/object_private.h // Must match size of compiler-generated OBJC_CLASS structure rdar://10640168 #define _OS_OBJECT_CLASS_HEADER() void *_os_obj_objc_class_t[5] 因此，_os_object_vtalbe_s的完整定义为:
typedef struct _os_object_vtable_s { void *_os_obj_objc_class_t[5]; } _os_object_vtable_s; 3.2 dispatch_object_s 与 dispatch_object_vtable_s
dispatch_object_s定义如下:
// 1. src/object_internal.h struct dispatch_object_s { _DISPATCH_OBJECT_HEADER(object); }; 宏_DISPATCH_OBJECT_HEADER的定义如下:
// 1. src/object_internal.h #define _DISPATCH_OBJECT_HEADER(x) _DISPATCH_OBJECT_HEADER_INTERNAL(x) struct dispatch_queue_s *do_targetq; void *do_ctxt; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; } // 2. src/object_internal.h #define _DISPATCH_OBJECT_HEADER(x) _DISPATCH_OBJECT_HEADER_INTERNAL(x) struct dispatch_queue_s *do_targetq; void *do_ctxt; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; } // 3. src/object_internal.h #define _DISPATCH_OBJECT_HEADER_INTERNAL(x) struct _os_object_s _as_os_obj[0]; OS_OBJECT_STRUCT_HEADER(dispatch_##x); struct dispatch_##x##_s *volatile do_next; // 4. src/object_internal.h #define OS_OBJECT_STRUCT_HEADER(x) _OS_OBJECT_HEADER( const struct x##_vtable_s *__ptrauth_objc_isa_pointer do_vtable, do_ref_cnt, do_xref_cnt) 因此，dispatch_object_s展开的完整结果为:
struct dispatch_object_s { // 这里就是 _os_object_s 内容 const struct dispatch_object_vtable_s *__ptrauth_objc_isa_pointer do_vtable, int volatile do_ref_cnt; int volatile do_xref_cnt; struct dispatch_object_s *volatile do_next; struct dispatch_queue_s *do_targetq; void *do_ctx; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; } }; 从展开的结果可以看到，dispatch_object_s的头部区域就是_os_object_s的内容，可以认为，dispatch_object_s"继承"自_os_object_s。
dispatch_object_vtable_s由宏DISPATCH_CLASS_DECL_BARE定义:
// 1. src/object_internal.h DISPATCH_CLASS_DECL_BARE(object, OBJECT); DISPATCH_CLASS_DECL_BARE正是组成DISPATCH_CLASS_DECL的第 3 个宏。
DISPATCH_CLASS_DECL_BARE的定义如下：
// 1. src/object_internal.h #define DISPATCH_CLASS_DECL_BARE(name, cluster) OS_OBJECT_CLASS_DECL(dispatch_##name, DISPATCH_##cluster##_VTABLE_HEADER(dispatch_##name)) 因此，宏DISPATCH_CLASS_DECL_BARE(name, OBJECT)扩展为:
OS_OBJECT_CLASS_DECL(dispatch_object, DISPATCH_OBJECT_VTALBE_HEADER(dispatch_object)) 宏DISPATCH_OBJECT_VTABLE_HEADER的定义如下:
// 1. src/object_internal.h #define DISPATCH_OBJECT_VTABLE_HEADER(x) unsigned long const do_type; void DISPATCH_VTABLE_ENTRY(do_dispose)(struct x##_s *, bool *allow_free); size_t DISPATCH_VTABLE_ENTRY(do_debug)(struct x##_s *, char *, size_t); void DISPATCH_VTABLE_ENTRY(do_invoke)(struct x##_s *, dispatch_invoke_context_t, dispatch_invoke_flags_t) // 2. src/internal.h #define DISPATCH_VTABLE_ENTRY(op) (* __ptrauth(ptrauth_key_process_independent_code, true, ptrauth_string_discriminator("dispatch." #op)) const op) 宏DISPATCH_VTALBE_ENTRY中的__ptrauth与PAC指针认证有关，与 GCD 功能无关，扩展结果中可以剔除这些扩展，因此宏DISPATCH_OBJECT_VTABLE_HEADER的扩展结果为:
unsigned const do_type; void * const do_dispose(struct dispatch_object_s *, bool *allow_free); size_t * const do_debug(struct dispatch_object_s *, char *, size_t); void * const do_invoke(struct dispatch_object_s *, dispatch_invoke_context_t, dispatch_invoke_flags_t); 宏OS_OBJECT_CLASS_DECL的定义如下:
// 1. src/object_internal.h #define OS_OBJECT_CLASS_DECL(name, ...) struct name##_s; struct name##_extra_vtable_s { __VA_ARGS__; }; struct name##_vtable_s { _OS_OBJECT_CLASS_HEADER(); struct name##_extra_vtable_s _os_obj_vtable; }; OS_OBJECT_EXTRA_VTABLE_DECL(name, name) extern const struct name##_vtable_s OS_OBJECT_CLASS_SYMBOL(name) __asm__(OS_OBJC_CLASS_RAW_SYMBOL_NAME(OS_OBJECT_CLASS(name))) // 2. os/object_private.h #define OS_OBJECT_CLASS_SYMBOL(name) OS_##name##_class // 3. os/object_private.h #define OS_OBJC_CLASS_RAW_SYMBOL_NAME(name) "_OBJC_CLASS_$_" OS_STRINGIFY(name) 上面代码中__VA_ARGS__就是宏DISPATCH_OBJECT_VTABLE_HEADER(dispatch_object)扩展的结果。因此宏DISPATCH_CLASS_DECL_BARE(object, OBJECT)扩展之后的结果为:
struct dispatch_object_s; struct dispatch_object_extra_vtable_s { unsigned const do_type; void * const do_dispose(struct dispatch_object_s *, bool *allow_free); size_t * const do_debug(struct dispatch_object_s *, char *, size_t); void * const do_invoke(struct dispatch_object_s *, dispatch_invoke_context_t, dispatch_invoke_flags_t); }; struct dispatch_object_vtable_s { void *_os_obj_objc_class_t[5]; struct dispatch_object_extra_vtable_s _os_obj_vtable; }; extern const struct dispatch_object_vtable_s OS_dispatch_object_class __asm__("_OBJC_CLASS_$_OS_dispatch_object"); 3.3 dispatch_queue_s 与 dispatch_queue_vtable_s
dispatch_queue_s的定义如下:
// 1. src/queue_internal.h struct dispatch_queue_s { DISPATCH_QUEUE_CLASS_HEADER(queue, void *__dq_opaque1); /* 32bit hole on LP64 */ } DISPATCH_ATOMIC64_ALIGN; // 2. src/queue_internal.h #define DISPATCH_QUEUE_CLASS_HEADER(x, __pointer_sized_field__) _DISPATCH_QUEUE_CLASS_HEADER(x, __pointer_sized_field__); /* LP64 global queue cacheline boundary */ unsigned long dq_serialnum; const char *dq_label; DISPATCH_UNION_LE(uint32_t volatile dq_atomic_flags, const uint16_t dq_width, const uint16_t __dq_opaque2 ); dispatch_priority_t dq_priority; union { struct dispatch_queue_specific_head_s *dq_specific_head; struct dispatch_source_refs_s *ds_refs; struct dispatch_timer_source_refs_s *ds_timer_refs; struct dispatch_mach_recv_refs_s *dm_recv_refs; struct dispatch_channel_callbacks_s const *dch_callbacks; }; int volatile dq_sref_cnt // 3. src/queue_internal.h #define _DISPATCH_QUEUE_CLASS_HEADER(x, __pointer_sized_field__) DISPATCH_OBJECT_HEADER(x); __pointer_sized_field__; DISPATCH_UNION_LE(uint64_t volatile dq_state, dispatch_lock dq_state_lock, uint32_t dq_state_bits ) // 4. src/object_internal.h #define DISPATCH_OBJECT_HEADER(x) struct dispatch_object_s _as_do[0]; _DISPATCH_OBJECT_HEADER(x) dispatch_queue_s完整的扩展结果如下:
struct disaptch_queue_s { // 头部 dispatch_object_s 内容 const struct dispatch_queue_vtable_s *__ptrauth_objc_isa_pointer do_vtable, int volatile do_ref_cnt; int volatile do_xref_cnt; struct dispatch_queue_s *volatile do_next; struct dispatch_queue_s *do_targetq; void *do_ctx; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; }; void *__dq_opaque1; union { uint64_t volatile dq_state; struct { dispatch_lock dq_state_lock; uint32_t dq_state_bits; }; }; /* LP64 global queue cacheline boundary */ unsigned long dq_serialnum; const char *dq_label; union { uint32_t volatile dq_atomic_flags; struct { const uint16_t dq_width; const uint16_t __dq_opaque2; }; }; dispatch_priority_t dq_priority; union { struct dispatch_queue_specific_head_s *dq_specific_head; struct dispatch_source_refs_s *ds_refs; struct dispatch_timer_source_refs_s *ds_timer_refs; struct dispatch_mach_recv_refs_s *dm_recv_refs; struct dispatch_channel_callbacks_s const *dch_callbacks; }; int volatile dq_sref_cnt } disaptch_queue_vtable_s由宏DISPATCH_CLASS_DECL定义:
// 1. src/queue_internal.h DISPATCH_CLASS_DECL(queue, QUEUE); // 2. src/object_internal.h #define DISPATCH_CLASS_DECL(name, cluster) _OS_OBJECT_DECL_PROTOCOL(dispatch_##name, dispatch_object) _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(dispatch_##name, dispatch_##name) DISPATCH_CLASS_DECL_BARE(name, cluster) 具体的说，是构成DISPATCH_CLASS_DECL宏的第 3 个宏DISPATCH_CLASS_BARE定义了dispatch_queue_vtable_s，完整的扩展结果为:
struct dispatch_queue_s; struct dispatch_queue_extra_vtable_s { unsigned long const do_type; void * const do_dispose(struct dispatch_queue_s *, bool *allow_free); size_t * const do_debug(struct dispatch_queue_s *, char *, size_t); void * const do_invoke(struct dispatch_queue_s *, dispatch_invoke_context_t, dispatch_qos_t); void * const dq_activate(dispatch_queue_class_t); void * const dq_wakeup(dispatch_queue_class_t, dispatch_qos_t, dispatch_wakeup_flags_t); void * const dq_push(dispatch_queue_class_t, dispatch_object_t, dispatch_qos_t); }; struct dispatch_queue_vtable_s { void *_os_obj_objc_class_t[5]; struct dispatch_queue_extra_vtable_s _os_obj_vtable; } extern const struct dispatch_queue_vtable_s OS_dispatch_queue_class __asm__("_OBJC_CLASS_$_OS_dispatch_queue"); 3.4 dispatch_lane_s 与 dispatch_lane_vtable_s
dispatch_lane_s的定义如下:
// 1. src/queue_internal.h typedef struct dispatch_lane_s { DISPATCH_LANE_CLASS_HEADER(lane); /* 32bit hole on LP64 */ } DISPATCH_ATOMIC64_ALIGN *dispatch_lane_t; // 2. src/queue_internal.h #define DISPATCH_LANE_CLASS_HEADER(x) struct dispatch_queue_s _as_dq[0]; DISPATCH_QUEUE_CLASS_HEADER(x, struct dispatch_object_s *volatile dq_items_tail); dispatch_unfair_lock_s dq_sidelock; struct dispatch_object_s *volatile dq_items_head; uint32_t dq_side_suspend_cnt 扩展之后的完整结果为:
typedef struct dispatch_lane_s { // 这里是 dispatch_queue_s const struct dispatch_lane_vtable_s *__ptrauth_objc_isa_pointer do_vtable; int volatile do_ref_cnt; int volatile do_xref_cnt; struct dispatch_lane_s *volatile do_next; struct dispatch_queue_s *do_targetq; void *do_ctxt; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; }; struct dispatch_object_s *volatile dq_items_tail; union { uint64_t volatile dq_state; struct { dispatch_lock dq_state_lock; uint32_t dq_state_bits; }; ); /* LP64 global queue cacheline boundary */ unsigned long dq_serialnum; const char *dq_label; union { uint32_t volatile dq_atomic_flags; struct { const uint16_t dq_width; const uint16_t __dq_opaque2; }; ); dispatch_priority_t dq_priority; union { struct dispatch_queue_specific_head_s *dq_specific_head; struct dispatch_source_refs_s *ds_refs; struct dispatch_timer_source_refs_s *ds_timer_refs; struct dispatch_mach_recv_refs_s *dm_recv_refs; struct dispatch_channel_callbacks_s const *dch_callbacks; }; int volatile dq_sref_cnt; dispatch_unfair_lock_s dq_sidelock; struct dispatch_object_s *volatile dq_items_head; uint32_t dq_side_suspend_cnt; } *dispatch_lane_t; dispatch_lane_vtable_s由宏DISPATCH_CLASS_DECL_BARE定义:
// 1. src/queue_internal.h DISPATCH_CLASS_DECL_BARE(lane, QUEUE); dispatch_lane_vtable_s由宏OS_OBJECT_SUBCLASS_DECL定义，完整的展开结果为:
struct dispatch_lane_s; struct dispatch_lane_extra_vtable_s { unsigned long const do_type; void * const do_dispose(struct dispatch_lane_s * bool *allow_free); size_t * const do_debug(struct dispatch_lane_s *, char *, size_t); void * const do_invoke(struct dispatch_lane_s * dispatch_invoke_context_t, dispatch_invoke_flags_t); void * const dq_activate(dispatch_queue_class_t); void * const dq_wakeup(dispatch_queue_class_t, dispatch_qos_t, dispatch_wakeup_flags_t); void * const dq_push(dispatch_queue_class_t, dispatch_object_t, dispatch_qos_t); } struct dispatch_lane_vtable_s { void *_os_obj_objc_class_t[5]; struct dispatch_lane_extra_vtable_s _os_obj_vtable; } extern const struct dispatch_lane_vtable_s OS_dispatch_lane_class __asm__("_OBJC_CLASS_$_OS_dispatch_lane") 与dispatch_lane_vtable_s有关的 3 个宏定义如下:
// 1. src/queue_internal.h DISPATCH_SUBCLASS_DECL(queue_serial, queue_serial_executor, lane); DISPATCH_SUBCLASS_DECL(queue_main, queue_serial, lane); DISPATCH_SUBCLASS_DECL(queue_concurrent, queue, lane); DISPATCH_SUBCLASS_DECL(queue_global, queue, lane); // 2. src/object_internal.h #define DISPATCH_SUBCLASS_DECL(name, super, ctype) _OS_OBJECT_DECL_PROTOCOL(dispatch_##name, dispatch_##super); _OS_OBJECT_CLASS_IMPLEMENTS_PROTOCOL(dispatch_##name, dispatch_##name) OS_OBJECT_SUBCLASS_DECL(dispatch_##name, dispatch_##ctype) // 3. src/object_internal.h // define a new subclass used in a cluster #define OS_OBJECT_SUBCLASS_DECL(name, ctype) struct name##_s; OS_OBJECT_EXTRA_VTABLE_DECL(name, ctype) extern const struct ctype##_vtable_s OS_OBJECT_CLASS_SYMBOL(name) __asm__(OS_OBJC_CLASS_RAW_SYMBOL_NAME(OS_OBJECT_CLASS(name))) 之前在第 2 部分没有介绍宏OS_OBJECT_SUBCLASS_DECL，这里继续介绍。
代码注释 1 处 4 个宏展开之后的结果为:
struct dispatch_queue_serial_s; extern const struct dispatch_lane_vtable_s OS_dispatch_queue_serial_class __asm__("_OBJC_CLASS_$_OS_dispatch_queue_serial"); struct dispatch_queue_main_s; extern const struct dispatch_lane_vtable_s OS_dispatch_queue_main_class __asm__("_OBJC_CLASS_$_OS_dispatch_queue_main"); struct dispatch_queue_concurrent_s; extern const struct dispatch_lane_vtable_s OS_dispatch_queue_concurrent_class __asm__("_OBJC_CLASS_$_OS_dispatch_concurrent"); struct dispatch_queue_global_s; extern const struct dispatch_lane_vtable_s OS_dispatch_queue_global_class __asm__("_OBJC_CLASS_$_OS_dispatch_queue_global"); ## 3.6 dispatch_queue_global_s `dispatch_queue_global_s`定义如下: ```c++ // 1. src/queue_internal.h struct dispatch_queue_global_s { DISPATCH_QUEUE_ROOT_CLASS_HEADER(lane); } DISPATCH_CACHELINE_ALIGN; // 2. src/queue_internal.h #define DISPATCH_QUEUE_ROOT_CLASS_HEADER(x) struct dispatch_queue_s _as_dq[0]; DISPATCH_QUEUE_CLASS_HEADER(x, struct dispatch_object_s *volatile dq_items_tail); int volatile dgq_thread_pool_size; struct dispatch_object_s *volatile dq_items_head; int volatile dgq_pending; 完整扩展结果如下:
typedef struct dispatch_queue_global_s { // 这里是 dispatch_queue_s const struct dispatch_lane_vtable_s *__ptrauth_objc_isa_pointer do_vtable; int volatile do_ref_cnt; int volatile do_xref_cnt; struct dispatch_lane_s *volatile do_next; struct dispatch_queue_s *do_targetq; void *do_ctxt; union { dispatch_function_t DISPATCH_FUNCTION_POINTER do_finalizer; void *do_introspection_ctxt; }; struct dispatch_object_s *volatile dq_items_tail; union { uint64_t volatile dq_state; struct { dispatch_lock dq_state_lock; uint32_t dq_state_bits; }; ); /* LP64 global queue cacheline boundary */ unsigned long dq_serialnum; const char *dq_label; union { uint32_t volatile dq_atomic_flags; struct { const uint16_t dq_width; const uint16_t __dq_opaque2; }; ); dispatch_priority_t dq_priority; union { struct dispatch_queue_specific_head_s *dq_specific_head; struct dispatch_source_refs_s *ds_refs; struct dispatch_timer_source_refs_s *ds_timer_refs; struct dispatch_mach_recv_refs_s *dm_recv_refs; struct dispatch_channel_callbacks_s const *dch_callbacks; }; int volatile dq_sref_cnt; int volatile dgq_thread_pool_size; struct dispatch_object_s *volatile dq_items_head; int volatile dgq_pending; } 3.7 dispatch_queue_class_t
dispatch_queue_class_t的定义如下：
// 1. src/internal.h // Dispatch queue cluster class: type for any dispatch_queue_t typedef union { struct dispatch_queue_s *_dq; struct dispatch_workloop_s *_dwl; struct dispatch_lane_s *_dl; struct dispatch_queue_static_s *_dsq; struct dispatch_queue_global_s *_dgq; struct dispatch_queue_pthread_root_s *_dpq; struct dispatch_source_s *_ds; struct dispatch_channel_s *_dch; struct dispatch_mach_s *_dm; dispatch_lane_class_t _dlu; #ifdef __OBJC__ id<OS_dispatch_queue> _objc_dq; #endif } dispatch_queue_class_t DISPATCH_TRANSPARENT_UNION;
