if we wait before sending the packets we dont need to store the received packets at all because the awaiter will always be there or is already canceled

MQTTnet.Core/Client/MqttPacketDispatcher.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using System.Threading.Tasks;
 using MQTTnet.Core.Diagnostics;
 using MQTTnet.Core.Exceptions;
@@ -11,8 +10,6 @@ namespace MQTTnet.Core.Client
 {
     public class MqttPacketDispatcher
     {
-        private readonly object _syncRoot = new object();
-        private readonly HashSet<MqttBasePacket> _receivedPackets = new HashSet<MqttBasePacket>();
         private readonly ConcurrentDictionary<Type, TaskCompletionSource<MqttBasePacket>> _packetByResponseType = new ConcurrentDictionary<Type, TaskCompletionSource<MqttBasePacket>>();
         private readonly ConcurrentDictionary<Type, ConcurrentDictionary<ushort,TaskCompletionSource<MqttBasePacket>>> _packetByResponseTypeAndIdentifier = new ConcurrentDictionary<Type, ConcurrentDictionary<ushort,TaskCompletionSource<MqttBasePacket>>>();
 
@@ -21,8 +18,6 @@ namespace MQTTnet.Core.Client
             if (request == null) throw new ArgumentNullException(nameof(request));
 
             var packetAwaiter = AddPacketAwaiter(request, responseType);
-            DispatchPendingPackets();
-
             try
             {
                 return await packetAwaiter.Task.TimeoutAfter(timeout);
@@ -43,8 +38,6 @@ namespace MQTTnet.Core.Client
             if (packet == null) throw new ArgumentNullException(nameof(packet));
 
             var type = packet.GetType();
-            var packetDispatched = false;
-
             if (packet is IMqttPacketWithIdentifier withIdentifier)
             {
                 if (_packetByResponseTypeAndIdentifier.TryGetValue(type, out var byid))
@@ -52,37 +45,19 @@ namespace MQTTnet.Core.Client
                     if (byid.TryRemove( withIdentifier.PacketIdentifier, out var tcs))
                     {
                         tcs.TrySetResult( packet );
-                        packetDispatched = true;
                     }
                 }
             }
             else if (_packetByResponseType.TryRemove(type, out var tcs))
             {
                 tcs.TrySetResult(packet);
-                packetDispatched = true;
-            }
-
-            lock (_syncRoot)
-            {
-                if (!packetDispatched)
-                {
-                    _receivedPackets.Add(packet);
-                }
-                else
-                {
-                    _receivedPackets.Remove(packet);
-                }
             }
         }
 
         public void Reset()
         {
-            lock (_syncRoot)
-            {
-                _receivedPackets.Clear();
-            }
-
             _packetByResponseTypeAndIdentifier.Clear();
+            _packetByResponseType.Clear();
         }
 
         private TaskCompletionSource<MqttBasePacket> AddPacketAwaiter(MqttBasePacket request, Type responseType)
@@ -113,19 +88,5 @@ namespace MQTTnet.Core.Client
                 _packetByResponseType.TryRemove(responseType, out var _);
             }
         }
-
-        private void DispatchPendingPackets()
-        {
-            List<MqttBasePacket> receivedPackets;
-            lock (_syncRoot)
-            {
-                receivedPackets = new List<MqttBasePacket>(_receivedPackets);
-            }
-
-            foreach (var pendingPacket in receivedPackets)
-            {
-                Dispatch(pendingPacket);
-            }
-        }
     }
 }