Replacement for Dictionary holding Clients

[Chroma72]

Fixed your dictionary issue:

 public class ExpiringCache
 {
     private ConcurrentDictionary<SocketAddress, (IPEndPoint endpoint, DateTime lastAccess)> _cache;
     private TimeSpan _expirationTime;
     private readonly Timer _cleanupTimer;

     public ExpiringCache(TimeSpan expirationTime)
     {
         _cache = new ConcurrentDictionary<SocketAddress, (IPEndPoint, DateTime)>();
         _expirationTime = expirationTime;
         _cleanupTimer = new Timer(Cleanup, null, _expirationTime, _expirationTime);
     }

     public IPEndPoint AddOrUpdateEndPoint(SocketAddress address)
     {
         var now = DateTime.UtcNow;

         // Check if the SocketAddress key already exists
         if (!_cache.TryGetValue(address, out var cacheEntry))
         {
             Console.WriteLine($"New client added.");
             // Create new IPEndPoint from SocketAddress
             var endpoint = new IPEndPoint(IPAddress.Any, 0);
             endpoint = (IPEndPoint)endpoint.Create(address);

             // Add to cache
             cacheEntry = (endpoint, now);
             _cache[address] = cacheEntry;
         }
         else
         {
             // Update last access time for existing entry
             Console.WriteLine($"Existing client activity updated.");
             cacheEntry = (cacheEntry.endpoint, now);
             _cache[address] = cacheEntry;
         }

         return cacheEntry.endpoint;
     }

     private void Cleanup(object state)
     {
         Console.WriteLine($"Performing client cleanup.");

         var now = DateTime.UtcNow;
         foreach (var kvp in _cache)
         {
             if (now - kvp.Value.lastAccess > _expirationTime)
             {
                 // Remove old entries
                 Console.WriteLine($"Client removed for inactivity.");
                 _cache.TryRemove(kvp.Key, out _);
             }
         }
     }
 }

[enclave-alistair]

There's a couple of issues/improvements here:

• Make sure to clone the SocketAddress when you insert it as a key into the dictionary; I made this mistake originally, and put the same instance into the dictionary, meaning the addresses would always be equal.

• Don't write to console, certainly not in the successful lookup case, that will lock on the console and generally ruin the performance.

• Because the entry in the dictionary is a struct, you should consider using CollectionsMarshal.GetValueRefOrNullRef to get a reference to the value type inside the dictionary, rather than needing to copy the value in and out of the dictionary when you update the time.

• Don't use DateTime.UtcNow to update; DateTime.UtcNow is relatively slow compared to something like Environment.TickCount64:

  | Method          | Mean      | Error     | StdDev    | Ratio |
  |---------------- |----------:|----------:|----------:|------:|
  | DateTime.UtcNow | 25.618 ns | 0.4870 ns | 0.8530 ns |  1.00 |
  | TickCount64     |  1.856 ns | 0.0737 ns | 0.2092 ns |  0.08 | 
  

  Because you only compare about relative time rather than absolute time, you can save a bunch of CPU cycles by using TickCount64, and store the long instead of the DateTime.

• There's no explicit disposal on this class to stop the Timer from running.