Refactor subscriptions manager

Frameworks/MQTTnet.NetStandard/Client/MqttClient.cs

@@ -290,18 +290,27 @@ namespace MQTTnet.Client
 
         private Task SendAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
-            _sendTracker.Restart();
-            return _adapter.SendPacketsAsync(_options.CommunicationTimeout, new[] { packet }, cancellationToken);
+            return SendAsync(new[] { packet }, cancellationToken);
         }
 
         private Task SendAsync(IEnumerable<MqttBasePacket> packets, CancellationToken cancellationToken)
         {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                throw new TaskCanceledException();
+            }
+
             _sendTracker.Restart();
             return _adapter.SendPacketsAsync(_options.CommunicationTimeout, packets, cancellationToken);
         }
 
         private async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttBasePacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttBasePacket
         {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                throw new TaskCanceledException();
+            }
+
             _sendTracker.Restart();
 
             ushort identifier = 0;
@@ -528,7 +537,7 @@ namespace MQTTnet.Client
 
         private static async Task WaitForTaskAsync(Task task, Task sender)
         {
-            if (task == sender)
+            if (task == sender || task == null)
             {
                 return;
             }

Frameworks/MQTTnet.NetStandard/Internal/AsyncAutoResetEvent.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Internal
+{
+    public sealed class AsyncAutoResetEvent : IDisposable
+    {
+        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(0, 1);
+
+        public Task WaitOneAsync(CancellationToken cancellationToken)
+        {
+            return _semaphore.WaitAsync(cancellationToken);
+        }
+
+        public void Set()
+        {
+            _semaphore.Release();
+        }
+
+        public void Dispose()
+        {
+            _semaphore?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetStandard/Internal/AsyncLock.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Internal
+{
+    public sealed class AsyncLock : IDisposable
+    {
+        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
+
+        public Task EnterAsync(CancellationToken cancellationToken)
+        {
+            return _semaphore.WaitAsync(cancellationToken);
+        }
+
+        public void Exit()
+        {
+            _semaphore.Release();
+        }
+
+        public void Dispose()
+        {
+            _semaphore?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetStandard/Server/MqttClientPendingMessagesQueue.cs

@@ -5,6 +5,7 @@ using System.Threading.Tasks;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 
@@ -13,7 +14,7 @@ namespace MQTTnet.Server
     public sealed class MqttClientPendingMessagesQueue : IDisposable
     {
         private readonly ConcurrentQueue<MqttBasePacket> _queue = new ConcurrentQueue<MqttBasePacket>();
-        private readonly SemaphoreSlim _queueWaitSemaphore = new SemaphoreSlim(0);
+        private readonly AsyncAutoResetEvent _queueAutoResetEvent = new AsyncAutoResetEvent();
         private readonly IMqttServerOptions _options;
         private readonly MqttClientSession _clientSession;
         private readonly IMqttNetLogger _logger;
@@ -54,7 +55,7 @@ namespace MQTTnet.Server
             if (packet == null) throw new ArgumentNullException(nameof(packet));
 
             _queue.Enqueue(packet);
-            _queueWaitSemaphore.Release();
+            _queueAutoResetEvent.Set();
 
             _logger.Verbose<MqttClientPendingMessagesQueue>("Enqueued packet (ClientId: {0}).", _clientSession.ClientId);
         }
@@ -82,7 +83,7 @@ namespace MQTTnet.Server
             MqttBasePacket packet = null;
             try
             {
-                await _queueWaitSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
+                await _queueAutoResetEvent.WaitOneAsync(cancellationToken).ConfigureAwait(false);
                 if (!_queue.TryDequeue(out packet))
                 {
                     throw new InvalidOperationException(); // should not happen
@@ -120,8 +121,8 @@ namespace MQTTnet.Server
                     if (publishPacket.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
                     {
                         publishPacket.Dup = true;
-                        _queue.Enqueue(packet);
-                        _queueWaitSemaphore.Release();
+
+                        Enqueue(publishPacket);
                     }
                 }
 
@@ -134,7 +135,7 @@ namespace MQTTnet.Server
 
         public void Dispose()
         {
-            _queueWaitSemaphore?.Dispose();
+            _queueAutoResetEvent?.Dispose();
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Server/MqttClientSession.cs

@@ -134,7 +134,7 @@ namespace MQTTnet.Server
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            var result = await SubscriptionsManager.CheckSubscriptionsAsync(applicationMessage);
+            var result = await SubscriptionsManager.CheckSubscriptionsAsync(applicationMessage).ConfigureAwait(false);
             if (!result.IsSubscribed)
             {
                 return;
@@ -155,10 +155,10 @@ namespace MQTTnet.Server
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            await SubscriptionsManager.SubscribeAsync(new MqttSubscribePacket
+            SubscriptionsManager.Subscribe(new MqttSubscribePacket
             {
                 TopicFilters = topicFilters
-            }).ConfigureAwait(false);
+            });
 
             await EnqueueSubscribedRetainedMessagesAsync(topicFilters).ConfigureAwait(false);
         }
@@ -167,10 +167,12 @@ namespace MQTTnet.Server
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            return SubscriptionsManager.UnsubscribeAsync(new MqttUnsubscribePacket
+            SubscriptionsManager.Unsubscribe(new MqttUnsubscribePacket
             {
                 TopicFilters = topicFilters
             });
+
+            return Task.FromResult(0);
         }
 
         public void Dispose()
@@ -288,7 +290,7 @@ namespace MQTTnet.Server
 
         private async Task HandleIncomingSubscribePacketAsync(IMqttChannelAdapter adapter, MqttSubscribePacket subscribePacket, CancellationToken cancellationToken)
         {
-            var subscribeResult = await SubscriptionsManager.SubscribeAsync(subscribePacket).ConfigureAwait(false);
+            var subscribeResult = SubscriptionsManager.Subscribe(subscribePacket);
             await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, new[] { subscribeResult.ResponsePacket }, cancellationToken).ConfigureAwait(false);
 
             if (subscribeResult.CloseConnection)
@@ -302,7 +304,7 @@ namespace MQTTnet.Server
 
         private async Task HandleIncomingUnsubscribePacketAsync(IMqttChannelAdapter adapter, MqttUnsubscribePacket unsubscribePacket, CancellationToken cancellationToken)
         {
-            var unsubscribeResult = await SubscriptionsManager.UnsubscribeAsync(unsubscribePacket).ConfigureAwait(false);
+            var unsubscribeResult = SubscriptionsManager.Unsubscribe(unsubscribePacket);
             await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, new[] { unsubscribeResult }, cancellationToken);
         }
 

Frameworks/MQTTnet.NetStandard/Server/MqttClientSubscriptionsManager.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -10,7 +11,7 @@ namespace MQTTnet.Server
 {
     public sealed class MqttClientSubscriptionsManager : IDisposable
     {
-        private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
+        private readonly ConcurrentDictionary<string, MqttQualityOfServiceLevel> _subscriptions = new ConcurrentDictionary<string, MqttQualityOfServiceLevel>();
         private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
         private readonly IMqttServerOptions _options;
         private readonly MqttServer _server;
@@ -23,7 +24,7 @@ namespace MQTTnet.Server
             _server = server;
         }
 
-        public async Task<MqttClientSubscribeResult> SubscribeAsync(MqttSubscribePacket subscribePacket)
+        public MqttClientSubscribeResult Subscribe(MqttSubscribePacket subscribePacket)
         {
             if (subscribePacket == null) throw new ArgumentNullException(nameof(subscribePacket));
 
@@ -37,57 +38,41 @@ namespace MQTTnet.Server
                 CloseConnection = false
             };
 
-            await _semaphore.WaitAsync().ConfigureAwait(false);
-            try
+            foreach (var topicFilter in subscribePacket.TopicFilters)
             {
-                foreach (var topicFilter in subscribePacket.TopicFilters)
+                var interceptorContext = InterceptSubscribe(topicFilter);
+                if (!interceptorContext.AcceptSubscription)
                 {
-                    var interceptorContext = InterceptSubscribe(topicFilter);
-                    if (!interceptorContext.AcceptSubscription)
-                    {
-                        result.ResponsePacket.SubscribeReturnCodes.Add(MqttSubscribeReturnCode.Failure);
-                    }
-                    else
-                    {
-                        result.ResponsePacket.SubscribeReturnCodes.Add(ConvertToMaximumQoS(topicFilter.QualityOfServiceLevel));
-                    }
+                    result.ResponsePacket.SubscribeReturnCodes.Add(MqttSubscribeReturnCode.Failure);
+                }
+                else
+                {
+                    result.ResponsePacket.SubscribeReturnCodes.Add(ConvertToMaximumQoS(topicFilter.QualityOfServiceLevel));
+                }
 
-                    if (interceptorContext.CloseConnection)
-                    {
-                        result.CloseConnection = true;
-                    }
+                if (interceptorContext.CloseConnection)
+                {
+                    result.CloseConnection = true;
+                }
 
-                    if (interceptorContext.AcceptSubscription)
-                    {
-                        _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
-                        _server.OnClientSubscribedTopic(_clientId, topicFilter);
-                    }
+                if (interceptorContext.AcceptSubscription)
+                {
+                    _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
+                    _server.OnClientSubscribedTopic(_clientId, topicFilter);
                 }
             }
-            finally
-            {
-                _semaphore.Release();
-            }
 
             return result;
         }
 
-        public async Task<MqttUnsubAckPacket> UnsubscribeAsync(MqttUnsubscribePacket unsubscribePacket)
+        public MqttUnsubAckPacket Unsubscribe(MqttUnsubscribePacket unsubscribePacket)
         {
             if (unsubscribePacket == null) throw new ArgumentNullException(nameof(unsubscribePacket));
 
-            await _semaphore.WaitAsync().ConfigureAwait(false);
-            try
+            foreach (var topicFilter in unsubscribePacket.TopicFilters)
             {
-                foreach (var topicFilter in unsubscribePacket.TopicFilters)
-                {
-                    _subscriptions.Remove(topicFilter);
-                    _server.OnClientUnsubscribedTopic(_clientId, topicFilter);
-                }
-            }
-            finally
-            {
-                _semaphore.Release();
+                _subscriptions.TryRemove(topicFilter, out _);
+                _server.OnClientUnsubscribedTopic(_clientId, topicFilter);
             }
 
             return new MqttUnsubAckPacket

Tests/MQTTnet.Core.Tests/AsyncAutoResentEventTests.cs

@@ -0,0 +1,34 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class AsyncAutoResetEventTests
+    {
+        [TestMethod]
+        public async Task AsyncAutoResetEvent()
+        {
+            var aare = new AsyncAutoResetEvent();
+
+            var increment = 0;
+            var globalI = 0;
+#pragma warning disable 4014
+            Task.Run(async () =>
+#pragma warning restore 4014
+            {
+                await aare.WaitOneAsync(CancellationToken.None);
+                globalI += increment;
+            });
+
+            await Task.Delay(500);
+            increment = 1;
+            aare.Set();
+            await Task.Delay(100);
+
+            Assert.AreEqual(1, globalI);
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/AsyncLockTests.cs

@@ -0,0 +1,44 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class AsyncLockTests
+    {
+        [TestMethod]
+        public void AsyncLock()
+        {
+            const int ThreadsCount = 10;
+
+            var threads = new Task[ThreadsCount];
+            var @lock = new AsyncLock();
+            var globalI = 0;
+            for (var i = 0; i < ThreadsCount; i++)
+            {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                threads[i] = Task.Run(async () =>
+                {
+                    await @lock.EnterAsync(CancellationToken.None);
+                    try
+                    {
+                        var localI = globalI;
+                        await Task.Delay(10); // Increase the chance for wrong data.
+                        localI++;
+                        globalI = localI;
+                    }
+                    finally
+                    {
+                       @lock.Exit();
+                    }
+                });
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            }
+            
+            Task.WaitAll(threads);
+            Assert.AreEqual(ThreadsCount, globalI);
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/MqttServerTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Diagnostics;
@@ -58,8 +59,8 @@ namespace MQTTnet.Core.Tests
                 await s.StartAsync(new MqttServerOptions());
 
                 var willMessage = new MqttApplicationMessageBuilder().WithTopic("My/last/will").WithAtMostOnceQoS().Build();
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2", willMessage);
+                var c1 = await serverAdapter.ConnectTestClient("c1");
+                var c2 = await serverAdapter.ConnectTestClient("c2", willMessage);
 
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
                 await c1.SubscribeAsync(new TopicFilterBuilder().WithTopic("#").Build());
@@ -90,8 +91,8 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
 
                 var message = new MqttApplicationMessageBuilder().WithTopic("a").WithAtLeastOnceQoS().Build();
@@ -149,7 +150,7 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
 
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
 
@@ -167,6 +168,40 @@ namespace MQTTnet.Core.Tests
             Assert.AreEqual(1, receivedMessagesCount);
         }
 
+        [TestMethod]
+        public async Task MqttServer_RetainedMessagesFlow()
+        {
+            var retainedMessage = new MqttApplicationMessageBuilder().WithTopic("r").WithPayload("r").WithRetainFlag().Build();
+            var serverAdapter = new TestMqttServerAdapter();
+            var s = new MqttFactory().CreateMqttServer(new[] { serverAdapter }, new MqttNetLogger());
+            await s.StartAsync(new MqttServerOptions());
+            var c1 = await serverAdapter.ConnectTestClient("c1");
+            await c1.PublishAsync(retainedMessage);
+            Thread.Sleep(500);
+            await c1.DisconnectAsync();
+            Thread.Sleep(500);
+
+            var receivedMessages = 0;
+            var c2 = await serverAdapter.ConnectTestClient("c2");
+            c2.ApplicationMessageReceived += (_, e) =>
+            {
+                receivedMessages++;
+            };
+
+            for (var i = 0; i < 5; i++)
+            {
+                await c2.UnsubscribeAsync("r");
+                await Task.Delay(500);
+                Assert.AreEqual(i, receivedMessages);
+
+                await c2.SubscribeAsync("r");
+                await Task.Delay(500);
+                Assert.AreEqual(i + 1, receivedMessages);
+            }
+
+            await c2.DisconnectAsync();
+        }
+
         [TestMethod]
         public async Task MqttServer_NoRetainedMessage()
         {
@@ -179,11 +214,11 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
                 await c1.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[3]).Build());
                 await c1.DisconnectAsync();
 
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
                 await c2.SubscribeAsync(new TopicFilterBuilder().WithTopic("retained").Build());
 
@@ -208,11 +243,11 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
                 await c1.PublishAndWaitForAsync(s, new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[3]).WithRetainFlag().Build());
                 await c1.DisconnectAsync();
 
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
                 await c2.SubscribeAsync(new TopicFilterBuilder().WithTopic("retained").Build());
 
@@ -237,14 +272,14 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
                 await c1.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[3]).WithRetainFlag().Build());
                 await c1.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[0]).WithRetainFlag().Build());
                 await c1.DisconnectAsync();
-                
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
-                
+
                 await Task.Delay(200);
                 await c2.SubscribeAsync(new TopicFilter("retained", MqttQualityOfServiceLevel.AtMostOnce));
                 await Task.Delay(500);
@@ -271,7 +306,7 @@ namespace MQTTnet.Core.Tests
 
                 await s.StartAsync(options);
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
 
                 await c1.PublishAndWaitForAsync(s, new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[3]).WithRetainFlag().Build());
                 await c1.DisconnectAsync();
@@ -291,7 +326,7 @@ namespace MQTTnet.Core.Tests
                 var options = new MqttServerOptions { Storage = storage };
                 await s.StartAsync(options);
 
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
                 await c2.SubscribeAsync(new TopicFilterBuilder().WithTopic("retained").Build());
 
@@ -322,8 +357,8 @@ namespace MQTTnet.Core.Tests
 
                 await s.StartAsync(options);
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
                 await c2.SubscribeAsync(new TopicFilterBuilder().WithTopic("test").Build());
 
                 var isIntercepted = false;
@@ -357,8 +392,8 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
 
                 c1.ApplicationMessageReceived += (_, e) =>
                 {
@@ -412,8 +447,8 @@ namespace MQTTnet.Core.Tests
             {
                 await s.StartAsync(new MqttServerOptions());
 
-                var c1 = await serverAdapter.ConnectTestClient(s, "c1");
-                var c2 = await serverAdapter.ConnectTestClient(s, "c2");
+                var c1 = await serverAdapter.ConnectTestClient("c1");
+                var c2 = await serverAdapter.ConnectTestClient("c2");
 
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
 

Tests/MQTTnet.Core.Tests/MqttSubscriptionsManagerTests.cs

@@ -18,7 +18,7 @@ namespace MQTTnet.Core.Tests
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());
 
-            sm.SubscribeAsync(sp).Wait();
+            sm.Subscribe(sp);
 
             var pp = new MqttApplicationMessage
             {
@@ -39,7 +39,7 @@ namespace MQTTnet.Core.Tests
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilter("A/B/C", MqttQualityOfServiceLevel.AtMostOnce));
 
-            sm.SubscribeAsync(sp).Wait();
+            sm.Subscribe(sp);
 
             var pp = new MqttApplicationMessage
             {
@@ -61,7 +61,7 @@ namespace MQTTnet.Core.Tests
             sp.TopicFilters.Add(new TopicFilter("#", MqttQualityOfServiceLevel.AtMostOnce));
             sp.TopicFilters.Add(new TopicFilter("A/B/C", MqttQualityOfServiceLevel.AtLeastOnce));
 
-            sm.SubscribeAsync(sp).Wait();
+            sm.Subscribe(sp);
 
             var pp = new MqttApplicationMessage
             {
@@ -82,7 +82,7 @@ namespace MQTTnet.Core.Tests
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());
 
-            sm.SubscribeAsync(sp).Wait();
+            sm.Subscribe(sp);
 
             var pp = new MqttApplicationMessage
             {
@@ -101,7 +101,7 @@ namespace MQTTnet.Core.Tests
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());
 
-            sm.SubscribeAsync(sp).Wait();
+            sm.Subscribe(sp);
 
             var pp = new MqttApplicationMessage
             {
@@ -113,7 +113,7 @@ namespace MQTTnet.Core.Tests
 
             var up = new MqttUnsubscribePacket();
             up.TopicFilters.Add("A/B/C");
-            sm.UnsubscribeAsync(up).Wait();
+            sm.Unsubscribe(up);
 
             Assert.IsFalse(sm.CheckSubscriptionsAsync(pp).Result.IsSubscribed);
         }

Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs

@@ -43,11 +43,30 @@ namespace MQTTnet.Core.Tests
             return Task.FromResult(0);
         }
 
-        public Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout, CancellationToken cancellationToken)
+        public async Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout, CancellationToken cancellationToken)
         {
             ThrowIfPartnerIsNull();
 
-            return Task.Run(() =>
+            if (timeout > TimeSpan.Zero)
+            {
+                using (var timeoutCts = new CancellationTokenSource(timeout))
+                using (var cts = CancellationTokenSource.CreateLinkedTokenSource(timeoutCts.Token, cancellationToken))
+                {
+                    return await Task.Run(() =>
+                    {
+                        try
+                        {
+                            return _incomingPackets.Take(cts.Token);
+                        }
+                        catch
+                        {
+                            return null;
+                        }
+                    }, cts.Token);
+                }
+            }
+
+            return await Task.Run(() =>
             {
                 try
                 {

Tests/MQTTnet.Core.Tests/TestMqttServerAdapter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Adapter;
 using MQTTnet.Client;
@@ -11,7 +12,7 @@ namespace MQTTnet.Core.Tests
     {
         public event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
         
-        public async Task<IMqttClient> ConnectTestClient(IMqttServer server, string clientId, MqttApplicationMessage willMessage = null)
+        public async Task<IMqttClient> ConnectTestClient(string clientId, MqttApplicationMessage willMessage = null)
         {
             var adapterA = new TestMqttCommunicationAdapter();
             var adapterB = new TestMqttCommunicationAdapter();
@@ -22,8 +23,6 @@ namespace MQTTnet.Core.Tests
                 new TestMqttCommunicationAdapterFactory(adapterA),
                 new MqttNetLogger());
 
-            var connected = WaitForClientToConnect(server, clientId);
-
             FireClientAcceptedEvent(adapterB);
 
             var options = new MqttClientOptions
@@ -34,29 +33,11 @@ namespace MQTTnet.Core.Tests
             };
 
             await client.ConnectAsync(options);
-            await connected;
+            SpinWait.SpinUntil(() => client.IsConnected);
 
             return client;
         }
         
-        private static Task WaitForClientToConnect(IMqttServer s, string clientId)
-        {
-            var tcs = new TaskCompletionSource<object>();
-
-            void Handler(object sender, Server.MqttClientConnectedEventArgs args)
-            {
-                if (args.Client.ClientId == clientId)
-                {
-                    s.ClientConnected -= Handler;
-                    tcs.SetResult(null);
-                }
-            }
-
-            s.ClientConnected += Handler;
-
-            return tcs.Task;
-        }
-
         private void FireClientAcceptedEvent(IMqttChannelAdapter adapter)
         {
             ClientAccepted?.Invoke(this, new MqttServerAdapterClientAcceptedEventArgs(adapter));