Resource Linked List

reflist.cpp

#include <iostream>
#include <vector>
#include <algorithm>

struct Resource;

struct ListLink {
    Resource* item;
    unsigned slot;
    bool used;

    ListLink()
    : item(nullptr), slot(0), used(false)
    {}

    ListLink(Resource *item, unsigned slot, bool used = false)
    : item(item), slot(slot), used(used)
    {}
};

struct Resource {
    std::string name;
    std::vector<ListLink> links;
    unsigned refCount = 0;

    Resource(const std::string& name)
    : name(name)
    {}

    unsigned AllocSlot() {
        // Find the first unused link in our vector of links.
        for (size_t slot = 0; slot < links.size(); ++slot) 
        {
            if (links[slot].used == true)
                continue;
            return slot;
        }

        // All links are currently in use! Push and return a new one!
        links.emplace_back();
        return links.size()-1;
    }

    void IncRef() {
        std::cout << "IncRef: " << name << "\n";
        ++refCount;
    }

    void DecRef() {
        std::cout << "DecRef: " << name << "\n";
        if (--refCount == 0)
            delete this;
    }
};

struct CommandBuffer {
    ListLink refs;
    
    void RefResource(Resource& res) {
        res.IncRef();

        unsigned slot = res.AllocSlot();
        res.links[slot] = refs;

        refs.item = &res;
        refs.slot = slot;
        refs.used = true;
    }

    void ReleaseAll() {
        ListLink& link = refs;
        while (link.item)
        {
            Resource* res = link.item;
            link.used = false;
            link = link.item->links[link.slot];
            res->DecRef();
        }
    }
};

int main() {

    Resource resA("A");
    Resource resB("B");
    Resource resC("C");

    CommandBuffer cmdA;
    CommandBuffer cmdB;

    cmdA.RefResource(resA);
    cmdA.RefResource(resB);
    
    cmdB.RefResource(resA);
    cmdB.RefResource(resC);

    cmdA.ReleaseAll();
    cmdB.ReleaseAll();

    return 0;
}