use blockingcollection for pipelining

MQTTnet.Core/Internal/AsyncAutoResetEvent.cs

@@ -1,32 +0,0 @@
-using System.Collections.Generic;
-using System.Threading.Tasks;
-
-namespace MQTTnet.Core.Internal
-{
-    public sealed class AsyncGate
-    {
-        private readonly Queue<TaskCompletionSource<bool>> _waitingTasks = new Queue<TaskCompletionSource<bool>>();
-
-        public Task WaitOneAsync()
-        {
-            var tcs = new TaskCompletionSource<bool>();
-            lock (_waitingTasks)
-            {
-                _waitingTasks.Enqueue(tcs);
-            }
-
-            return tcs.Task;
-        }
-
-        public void Set()
-        {
-            lock (_waitingTasks)
-            {
-                if (_waitingTasks.Count > 0)
-                {
-                    _waitingTasks.Dequeue().SetResult(true);
-                }
-            }
-        }
-    }
-}

MQTTnet.Core/Server/MqttClientMessageQueue.cs

@@ -1,20 +1,17 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
+using System.Collections.Concurrent;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Core.Adapter;
 using MQTTnet.Core.Diagnostics;
 using MQTTnet.Core.Exceptions;
-using MQTTnet.Core.Internal;
 using MQTTnet.Core.Packets;
 
 namespace MQTTnet.Core.Server
 {
     public sealed class MqttClientMessageQueue
     {
-        private readonly List<MqttClientPublishPacketContext> _pendingPublishPackets = new List<MqttClientPublishPacketContext>();
-        private readonly AsyncGate _gate = new AsyncGate();
+        private readonly BlockingCollection<MqttClientPublishPacketContext> _pendingPublishPackets = new BlockingCollection<MqttClientPublishPacketContext>();
 
         private readonly MqttServerOptions _options;
         private CancellationTokenSource _cancellationTokenSource;
@@ -43,55 +40,38 @@ namespace MQTTnet.Core.Server
             _adapter = null;
             _cancellationTokenSource?.Cancel();
             _cancellationTokenSource = null;
+            _pendingPublishPackets?.Dispose();
         }
 
         public void Enqueue(MqttPublishPacket publishPacket)
         {
             if (publishPacket == null) throw new ArgumentNullException(nameof(publishPacket));
 
-            lock (_pendingPublishPackets)
-            {
-                _pendingPublishPackets.Add(new MqttClientPublishPacketContext(publishPacket));
-                _gate.Set();
-            }
+            _pendingPublishPackets.Add( new MqttClientPublishPacketContext( publishPacket ) );
         }
 
         private async Task SendPendingPublishPacketsAsync(CancellationToken cancellationToken)
         {
-            while (!cancellationToken.IsCancellationRequested)
+            foreach (var publishPacket in _pendingPublishPackets.GetConsumingEnumerable(cancellationToken))
             {
                 try
                 {
-                    await _gate.WaitOneAsync().ConfigureAwait(false);
-                    if (cancellationToken.IsCancellationRequested)
+                    if ( cancellationToken.IsCancellationRequested )
                     {
                         return;
                     }
 
-                    if (_adapter == null)
+                    if ( _adapter == null )
                     {
                         continue;
                     }
 
-                    List<MqttClientPublishPacketContext> pendingPublishPackets;
-                    lock (_pendingPublishPackets)
-                    {
-                        pendingPublishPackets = _pendingPublishPackets.ToList();
-                    }
-
-                    foreach (var publishPacket in pendingPublishPackets)
-                    {
-                        await TrySendPendingPublishPacketAsync(publishPacket).ConfigureAwait(false);
-                    }
+                    await TrySendPendingPublishPacketAsync( publishPacket ).ConfigureAwait( false );
                 }
-                catch (Exception e)
+                catch ( Exception e )
                 {
-                    MqttTrace.Error(nameof(MqttClientMessageQueue), e, "Error while sending pending publish packets.");
+                    MqttTrace.Error( nameof( MqttClientMessageQueue ), e, "Error while sending pending publish packets." );
                 }
-                finally
-                {
-                    Cleanup();
-                }               
             }
         }
 
@@ -112,23 +92,17 @@ namespace MQTTnet.Core.Server
             catch (MqttCommunicationException exception)
             {
                 MqttTrace.Warning(nameof(MqttClientMessageQueue), exception, "Sending publish packet failed.");
+                _pendingPublishPackets.Add( publishPacketContext );
             }
             catch (Exception exception)
             {
                 MqttTrace.Error(nameof(MqttClientMessageQueue), exception, "Sending publish packet failed.");
+                _pendingPublishPackets.Add( publishPacketContext );
             }
             finally
             {
                 publishPacketContext.SendTries++;
             }
         }
-
-        private void Cleanup()
-        {
-            lock (_pendingPublishPackets)
-            {
-                _pendingPublishPackets.RemoveAll(p => p.IsSent);
-            }
-        }
     }
 }