Question

I have such code

    senders.FirstOrDefault(sender => !sender.IsBusy);

This line is called pretty often.

The problem is that it always returns the first non-busy sender; the same first sender is returned pretty often, but the last one is returned very rarely. How to easily balance this?

Ideally, on every call I should return the most rarely used sender. I.e. between all non-busy senders select the one that was selected the least number of times during the last second.

Answer 1

If you want to get the least used one efficiently you will be probably good with the following non-Linq ‘list rotation’ solution, which is O(n) effiency and O(1) space unlike most of others:

// keep track of these
List<Sender> senders;
int nSelected = 0;          // number of already selected senders

// ...

// solution
int total = senders.Count;  // total number of senders
// looking for next non-busy sender
Sender s = null;
for (int i = 0; i < total; i++)
{
    int ind = (i + nSelected) % total; // getting the one 'after' previous
    if (!senders[ind].IsBusy)
    {
        s = senders[ind];
        ++nSelected;
        break;
    }
}

Of course this adds the must-be-indexable constraint on senders container.