Question

I’m trying to write a simple Resource Manager for the little hobby game I’m writing. One of the tasks that this resource manager needs to do is unloading unused resources. I can think of doing this in two ways:

• When an object no longer requires a
  reference to the resource, it must
  call a method of the Resource Manager
  to signify it is no longer using it;
  or

• When an object no longer requires a
  reference to the resource, it simply
  sets it to null. Then when the
  Resource Manager is asked to unload
  unused resources, it gets the
  reference count (via reflection?) of
  each resource. If the reference count
  is one (the Resource Manager will
  have a reference to the resource),
  unload the resource.

Is there any way to acheive the second solution in C#?
Thanks.

Answer 1

It sounds to me that you could just use WeakReference from the resource manager. The GC will do the rest. You’ll need to do a little casting, but it will be simple, and will work.

class Manager {
    Dictionary<string, WeakReference> refs =
        new Dictionary<string, WeakReference>();
    public object this[string key] {
        get {
            WeakReference wr;
            if (refs.TryGetValue(key, out wr)) {
                if(wr.IsAlive) return wr.Target;
                refs.Remove(key);
            }
            return null;
        }
        set {
            refs[key] = new WeakReference(value);
        }
    }
}
static void Main() {
    Manager mgr = new Manager();
    var obj = new byte[1024];
    mgr["abc"] = obj;

    GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
    Console.WriteLine(mgr["abc"] != null); // true (still ref'd by "obj")

    obj = null;
    GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
    Console.WriteLine(mgr["abc"] != null); // false (no remaining refs)
}