Method callback

src/core/impl/comp_node/comp_node.cpp:316–400

//! environments that do not provide large alignment support.
#if defined(MGB_MAX_SECTION_ALIGNMENT) && MGB_MAX_SECTION_ALIGNMENT < 64
struct comp_node_detail::DepedentObjList::StaticInfo {
#else
// use a large alignment to avoid cache line pollution
struct alignas(64) comp_node_detail::DepedentObjList::StaticInfo {
#endif
    Spinlock lock;
    DepedentObjList* head;
};
comp_node_detail::DepedentObjList::StaticInfo
        comp_node_detail::DepedentObjList::sm_info;

class comp_node_detail::DepedentObjList::Sentinel final
        : public comp_node_detail::DepedentObjList {
    std::shared_ptr<void> callback() override { return {}; }

public:
    Sentinel() { init_list(); }

    void init_list() {
        sm_info.head = this;
        m_next = m_prev = this;
    }

    static Sentinel* get() {
        // no need to delete; use static storage to avoid its dtor being invoked
        static std::aligned_storage_t<sizeof(Sentinel), alignof(Sentinel)> storage;
        static Sentinel* ptr = new (&storage) Sentinel{};
        return ptr;
    }
};

void comp_node_detail::DepedentObjList::add(DepedentObjList* ptr) {
    MGB_LOCK_GUARD(sm_info.lock);
    // if this becomes slow (which I do not think is likely to happen), we can
    // try a lock-free list implementation
    Sentinel::get();
    auto a = sm_info.head, b = a->m_next;
    // insert and delete from head, so items added last can be deleted first
    link(a, ptr);
    link(ptr, b);
}

void comp_node_detail::DepedentObjList::remove(DepedentObjList* ptr) {
    if (ptr->m_prev) {
        MGB_LOCK_GUARD(sm_info.lock);
        link(ptr->m_prev, ptr->m_next);
    }
}

void comp_node_detail::DepedentObjList::invoke_callback_and_clean() {
    SmallVector<std::shared_ptr<void>> refholds;
    {
        MGB_LOCK_GUARD(sm_info.lock);
        auto st = Sentinel::get();
        for (DepedentObjList *i = st->m_next, *inext; i != st; i = inext) {
            inext = i->m_next;
            i->m_prev = i->m_next = nullptr;
            auto ref = i->callback();