iOS底层原理探索-关联对象

static inline void reallySetProperty(id self, SEL _cmd, id newValue, ptrdiff_t offset, bool atomic, bool copy, bool mutableCopy)
{
    if (offset == 0) {
        object_setClass(self, newValue);
        return;
    }

    id oldValue;
    id *slot = (id*) ((char*)self + offset);

    if (copy) {
        newValue = [newValue copyWithZone:nil];
    } else if (mutableCopy) {
        newValue = [newValue mutableCopyWithZone:nil];
    } else {
        if (*slot == newValue) return;
        newValue = objc_retain(newValue);
    }

    if (!atomic) {
        oldValue = *slot;
        *slot = newValue;
    } else {
        spinlock_t& slotlock = PropertyLocks[slot];
        slotlock.lock();
        oldValue = *slot;
        *slot = newValue;        
        slotlock.unlock();
    }

    objc_release(oldValue);
}

id objc_getProperty(id self, SEL _cmd, ptrdiff_t offset, BOOL atomic) {
    if (offset == 0) {
        return object_getClass(self);
    }

    // Retain release world
    id *slot = (id*) ((char*)self + offset);
    if (!atomic) return *slot;
        
    // Atomic retain release world
    spinlock_t& slotlock = PropertyLocks[slot];
    slotlock.lock();
    id value = objc_retain(*slot);
    slotlock.unlock();
    
    // for performance, we (safely) issue the autorelease OUTSIDE of the spinlock.
    return objc_autoreleaseReturnValue(value);
}

// 声明
llvm::FunctionCallee GetOptimizedPropertySetFunction(bool atomic,
                                                     bool copy) override {
  return ObjCTypes.getOptimizedSetPropertyFn(atomic, copy);
}

llvm::FunctionCallee getOptimizedSetPropertyFn(bool atomic, bool copy) {
  CodeGen::CodeGenTypes &Types = CGM.getTypes();
  ASTContext &Ctx = CGM.getContext();
  
  SmallVector<CanQualType,4> Params;
  CanQualType IdType = Ctx.getCanonicalParamType(Ctx.getObjCIdType());
  CanQualType SelType = Ctx.getCanonicalParamType(Ctx.getObjCSelType());
  Params.push_back(IdType);
  Params.push_back(SelType);
  Params.push_back(IdType);
  Params.push_back(Ctx.getPointerDiffType()->getCanonicalTypeUnqualified());
  llvm::FunctionType *FTy =
      Types.GetFunctionType(
        Types.arrangeBuiltinFunctionDeclaration(Ctx.VoidTy, Params));
  const char *name;
  if (atomic && copy)
    name = "objc_setProperty_atomic_copy";
  else if (atomic && !copy)
    name = "objc_setProperty_atomic";
  else if (!atomic && copy)
    name = "objc_setProperty_nonatomic_copy";
  else
    name = "objc_setProperty_nonatomic";

  return CGM.CreateRuntimeFunction(FTy, name);
}

// 调用
llvm::FunctionCallee setOptimizedPropertyFn = nullptr;
llvm::FunctionCallee setPropertyFn = nullptr;
if (UseOptimizedSetter(CGM)) {
  // 10.8 and iOS 6.0 code and GC is off
  setOptimizedPropertyFn =
      CGM.getObjCRuntime().GetOptimizedPropertySetFunction(
          strategy.isAtomic(), strategy.isCopy());
  if (!setOptimizedPropertyFn) {
    CGM.ErrorUnsupported(propImpl, "Obj-C optimized setter - NYI");
    return;
  }
}
else {
  setPropertyFn = CGM.getObjCRuntime().GetPropertySetFunction();
  if (!setPropertyFn) {
    CGM.ErrorUnsupported(propImpl, "Obj-C setter requiring atomic copy");
    return;
  }
}

@interface Person : NSObject

@property (nonatomic, strong) NSString *name;

@end

@interface NSObject (Test)

@property (nonatomic, strong) NSString *test_name;

@end
 
@implementation NSObject (Test)

@end

#import "NSObject+Test.h"
#import <objc/runtime.h>

@implementation NSObject (Test)

- (void)setTest_name:(NSString *)test_name {
    objc_setAssociatedObject(self, @selector(test_name), test_name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)test_name {
    return objc_getAssociatedObject(self, _cmd);
}

@end

OBJC_EXPORT void
objc_setAssociatedObject(id _Nonnull object, const void * _Nonnull key,
                         id _Nullable value, objc_AssociationPolicy policy)
    OBJC_AVAILABLE(10.6, 3.1, 9.0, 1.0, 2.0);

OBJC_EXPORT id _Nullable
objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key)
    OBJC_AVAILABLE(10.6, 3.1, 9.0, 1.0, 2.0);

typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
    OBJC_ASSOCIATION_ASSIGN = 0,           /**< Specifies a weak reference to the associated object. */
    OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
                                            *   The association is made atomically. */
    OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
                                            *   The association is made atomically. */
};

void
objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
{
    SetAssocHook.get()(object, key, value, policy);
}

SetAssocHook.get()(object, key, value, policy) <==> base_objc_setAssociatedObject(object, key, value, policy)

static void
_base_objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
{
  _object_set_associative_reference(object, key, value, policy);
}

void
_object_set_associative_reference(id object, const void *key, id value, uintptr_t policy)
{
    // This code used to work when nil was passed for object and key. Some code
    // probably relies on that to not crash. Check and handle it explicitly.
    // rdar://problem/44094390
    if (!object && !value) return;

    if (object->getIsa()->forbidsAssociatedObjects())
        _objc_fatal("objc_setAssociatedObject called on instance (%p) of class %s which does not allow associated objects", object, object_getClassName(object));
    //object封装成一个数组结构类型，类型为DisguisedPtr
    DisguisedPtr<objc_object> disguised{(objc_object *)object};//相当于包装了一下 对象object,便于使用
    // 包装一下 policy - value
    ObjcAssociation association{policy, value};

    // retain the new value (if any) outside the lock.
    association.acquireValue();//根据策略类型进行处理
    //局部作用域空间
    {
        //初始化manager变量，相当于自动调用AssociationsManager的析构函数进行初始化
        AssociationsManager manager;//并不是全场唯一，构造函数中加锁只是为了避免重复创建，在这里是可以初始化多个AssociationsManager变量的
    
        AssociationsHashMap &associations(manager.get());//AssociationsHashMap 全场唯一

        if (value) {
            auto refs_result = associations.try_emplace(disguised, ObjectAssociationMap{});//返回的结果是一个类对
            if (refs_result.second) {//判断第二个存不存在，即bool值是否为true
                /* it's the first association we make 第一次建立关联*/
                object->setHasAssociatedObjects();//nonpointerIsa ，标记位true
            }

            /* establish or replace the association 建立或者替换关联*/
            auto &refs = refs_result.first->second; //得到一个空的桶子，找到引用对象类型,即第一个元素的second值
            auto result = refs.try_emplace(key, std::move(association));//查找当前的key是否有association关联对象
            if (!result.second) {//如果结果不存在
                association.swap(result.first->second);
            }
        } else {//如果传的是空值，则移除关联，相当于移除
            auto refs_it = associations.find(disguised);
            if (refs_it != associations.end()) {
                auto &refs = refs_it->second;
                auto it = refs.find(key);
                if (it != refs.end()) {
                    association.swap(it->second);
                    refs.erase(it);
                    if (refs.size() == 0) {
                        associations.erase(refs_it);

                    }
                }
            }
        }
    }

    // release the old value (outside of the lock).
    association.releaseHeldValue();//释放
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *obj = [Person new];
        objc_setAssociatedObject(obj, @selector(hello), @"Hello", OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return 0;
}

auto refs_it = associations.find(disguised); // 获取ObjectAssociationMap
if (refs_it != associations.end()) {
    auto &refs = refs_it->second;
    auto it = refs.find(key); // 获取ObjectAssociation
    if (it != refs.end()) {
        association.swap(it->second);
        refs.erase(it); // 擦除ObjectAssociation
        if (refs.size() == 0) { // ObjectAssociationMap为空
            associations.erase(refs_it); // 擦除ObjectAssociationMapc

        }
    }
}

id
objc_getAssociatedObject(id object, const void *key)
{
    return _object_get_associative_reference(object, key);
}

id
_object_get_associative_reference(id object, const void *key)
{
    ObjcAssociation association{};//创建空的关联对象

    {
        AssociationsManager manager;//创建一个AssociationsManager管理类
        AssociationsHashMap &associations(manager.get());//获取全局唯一的静态哈希map
        AssociationsHashMap::iterator i = associations.find((objc_object *)object);//找到迭代器，即获取buckets
        if (i != associations.end()) {//如果这个迭代查询器不是最后一个 获取
            ObjectAssociationMap &refs = i->second; //找到ObjectAssociationMap的迭代查询器获取一个经过属性修饰符修饰的value
            ObjectAssociationMap::iterator j = refs.find(key);//根据key查找ObjectAssociationMap，即获取bucket
            if (j != refs.end()) {
                association = j->second;//获取ObjcAssociation
                association.retainReturnedValue();
            }
        }
    }

    return association.autoreleaseReturnedValue();//返回value
}

void objc_removeAssociatedObjects(id object) 
{
    if (object && object->hasAssociatedObjects()) {
        _object_remove_assocations(object);
    }
}

void
_object_remove_assocations(id object)
{
    ObjectAssociationMap refs{};//创建空的关联对象集合

    {
        AssociationsManager manager;//创建一个AssociationsManager管理类
        AssociationsHashMap &associations(manager.get());//获取全局唯一的静态哈希map
        AssociationsHashMap::iterator i = associations.find((objc_object *)object);//找到迭代器，即获取buckets
        if (i != associations.end()) {//如果这个迭代查询器不是最后一个 获取
            refs.swap(i->second);//获取ObjcAssociation
            associations.erase(i);//删除
        }
    }

    // release everything (outside of the lock).
    for (auto &i: refs) {
        i.second.releaseHeldValue();
    }
}