1001.png

id
_object_get_associative_reference(id object, const void *key)
{
    ObjcAssociation association{};

    {
        AssociationsManager manager;
        AssociationsHashMap &associations(manager.get());
        AssociationsHashMap::iterator i = associations.find((objc_object *)object);
        if (i != associations.end()) {
            ObjectAssociationMap &refs = i->second;
            ObjectAssociationMap::iterator j = refs.find(key);
            if (j != refs.end()) {
                association = j->second;
                association.retainReturnedValue();
            }
        }
    }

    return association.autoreleaseReturnedValue();
}

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));

    DisguisedPtr<objc_object> disguised{(objc_object *)object};
    ObjcAssociation association{policy, value};

    // retain the new value (if any) outside the lock.
    association.acquireValue();

    bool isFirstAssociation = false;
    {
        AssociationsManager manager;
        AssociationsHashMap &associations(manager.get());

        if (value) {
            auto refs_result = associations.try_emplace(disguised, ObjectAssociationMap{});
            if (refs_result.second) {
                /* it's the first association we make */
                isFirstAssociation = true;
            }

            /* establish or replace the association */
            auto &refs = refs_result.first->second;
            auto result = refs.try_emplace(key, std::move(association));
            if (!result.second) {
                association.swap(result.first->second);
            }
        } else {
            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);

                    }
                }
            }
        }
    }

    // Call setHasAssociatedObjects outside the lock, since this
    // will call the object's _noteAssociatedObjects method if it
    // has one, and this may trigger +initialize which might do
    // arbitrary stuff, including setting more associated objects.
    if (isFirstAssociation)
        object->setHasAssociatedObjects();

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

關(guān)聯(lián)對(duì)象：設(shè)置流程
1：創(chuàng)建一個(gè)AssociationsManager 管理類
2：獲取唯一的全局靜態(tài)哈希Map
3：判斷是否插入的關(guān)鍵值是否存在：
3.1存在走第四步
3.2 不存在就走：關(guān)聯(lián)對(duì)象插入空流程
4：創(chuàng)建一個(gè)空的 ObjectAssociationMap 去取查詢的鍵值對(duì)
5：如果發(fā)現(xiàn)沒(méi)有這個(gè)key就插入一個(gè)空的 BucketT 進(jìn)去返回
6:標(biāo)記對(duì)象存在關(guān)聯(lián)對(duì)象
7：用當(dāng)前修飾策略 和值 組成了一個(gè) ObjectAssociation 替換原來(lái)的 BucketT中的空
8：標(biāo)記一下ObjectAssociationMap的第一次為false
關(guān)聯(lián)對(duì)象插入空流程
1：根據(jù)DisguisedPtr 找到AssociationHashMap 中的iterator 迭代查詢器
2：清理迭代器
3：其實(shí)如果插入空置 相當(dāng)于清除
關(guān)聯(lián)對(duì)象：取值流程
1：創(chuàng)建一個(gè)AssociationsManager 管理類
2：獲取唯一的全局靜態(tài)哈希 map
3：根據(jù)DisguisedPtr 找到AssociationHashMap 中的iterator 迭代查詢器
4：如果這個(gè)迭代查詢器不是最后一個(gè) 獲取 ObjectAssociationMap（這里有策略和值）
5：找到AssociationHashMap的迭代查詢器獲取一個(gè)經(jīng)過(guò)屬性修飾符修飾的value
6：返回_value
總結(jié)：倆層哈希map，存取的時(shí)候倆層處理（類似二位數(shù)組）