public IDMultisetItemList PotentialFriendsPLinq(SubscriberID id, int maxCandidates)
{
var candidates =
subscribers[id].Friends.AsParallel() // Map
.SelectMany(friend => subscribers[friend].Friends)
.Where(foaf => foaf != id && !(subscribers[id].Friends.Contains(foaf))) // remove self, own friends
.GroupBy(foaf => foaf) // Reduce
.Select(foafGroup => new IDMultisetItem(foafGroup.Key, foafGroup.Count()));
return(Multiset.MostNumerous(candidates, maxCandidates)); // postprocess results of Reduce
}
public IDMultisetItemList PotentialFriendsParallel(SubscriberID id, int maxCandidates)
{
object locker = new object();
IDMultiset candidates = new IDMultiset();
Parallel.ForEach(subscribers[id].Friends, // Map over friends
() => Multiset.Create(new HashSet <SubscriberID>()), // init thread-local state localFoafs with empty Multiset
(friend, loopState, localFoafs) =>
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id || subscribers[id].Friends.Contains(foaf)); // remove self, own friends
return(Multiset.Union(localFoafs, Multiset.Create(foafs))); // Reduce, thread-local
},
localFoafs => { lock (locker) candidates = Multiset.Union(localFoafs, candidates); }); // Reduce, among threads
return(Multiset.MostNumerous(candidates, maxCandidates)); // postprocess results of Reduce
}
public IDMultisetItemList PotentialFriendsSequential(SubscriberID id, int maxCandidates)
{
// Map
var foafsList = new List <IDMultiset>();
foreach (SubscriberID friend in subscribers[id].Friends)
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id || subscribers[id].Friends.Contains(foaf)); // remove self, own friends
foafsList.Add(Multiset.Create(foafs));
}
// Reduce
IDMultiset candidates = new IDMultiset();
foreach (IDMultiset foafs in foafsList)
{
candidates = Multiset.Union(foafs, candidates);
}
// Postprocess
return(Multiset.MostNumerous(candidates, maxCandidates));
}