public IObservable <Change <TObject, TKey> > Watch(TKey key)
{
return(Observable.Create <Change <TObject, TKey> >
(
observer =>
{
lock (_locker)
{
//Create or find the existing subscribers
var existing = _subscribers.Lookup(key);
SubjectWithRefCount <Change <TObject, TKey> > subject;
if (existing.HasValue)
{
subject = existing.Value;
}
else
{
subject = new SubjectWithRefCount <Change <TObject, TKey> >(new ReplaySubject <Change <TObject, TKey> >(1));
var initial = _source.Lookup(key);
if (initial.HasValue)
{
var update = new Change <TObject, TKey>(ChangeReason.Add, key, initial.Value);
subject.OnNext(update);
}
_subscribers.BatchUpdate(updater => updater.AddOrUpdate(subject, key));
}
//set up subscription
var subscriber = subject.Subscribe(observer);
return Disposable.Create(() =>
{
//lock to ensure no race condition where the same key could be subscribed
//to whilst disposal is taking place
lock (_locker)
{
subscriber.Dispose();
if (subject.RefCount == 0)
{
_subscribers.BatchUpdate(updater => updater.Remove(key));
}
}
});
}
}));
}
internal void Update(Action <IIntermediateUpdater <TObject, TKey> > updateAction)
{
_cache.BatchUpdate(updateAction);
}