Vfrdtyky

In my code I got an ConcurrentDictionary now I want to iterate over each element in the Dictionary, but if a condition is true I want to remove an element from this Dictionary so I can't use a foreach loop. Also it might happen that the Dictionary will get a new element while in the loop or get one removed from a different thread. After some research I ended up using ElementAt.

Now my question is if the ConcurrentDictionary will release the indexes again like a List does. So that the first element will always have the index 0.

This is what my code looks like, CommandHandler.Timeouter is from ConcurrentDictionary:

int current = 0;



while (CommandHandler.Timeouter.Count() > current)

{

    var info = CommandHandler.Timeouter.ElementAt(current);

    var timeoutcooldown = info.Value.LastCommandTime.AddMinutes(1);



    if (timeoutcooldown < DateTime.UtcNow)

       {

           CommandHandler.Timeouter.TryRemove(info.Key, out _);

       }

    else current++;

}

ElementAt just treats the dictionary as an IEnumerable<KeyValuePair<TKey, TValue>>. Dictionaries are not ordered. The index is therefore meaningless. Think of the elements coming back in random order each time. Also, ElementAt has no way to make this thread safe.

It seems you want to implement cache expiration. Consider just using lock to access a normal dictionary. If there is not much contention this will be the simplest solution and very fast.

An alternative code pattern to this loop would be this:

var itemsToExpire = myDict.Where(/* compute expiration */).ToList();

foreach (var item in itemsToExpire)

   myDict.Remove(item);

No need for any complicated looping.