Merge pull request #270 from sebastienwarin/develop

Replace the Async coordination primitives & replace the MqttTopicFilterComparer to improve the performance

Frameworks/MQTTnet.NetStandard/Internal/AsyncAutoResetEvent.cs

@@ -1,26 +1,108 @@
 using System;
+using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 
 namespace MQTTnet.Internal
 {
-    public sealed class AsyncAutoResetEvent : IDisposable
+    // Inspired from Stephen Toub (https://blogs.msdn.microsoft.com/pfxteam/2012/02/11/building-async-coordination-primitives-part-2-asyncautoresetevent/) and Chris Gillum (https://stackoverflow.com/a/43012490)
+    public class AsyncAutoResetEvent
     {
-        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(0, 1);
+        private readonly LinkedList<TaskCompletionSource<bool>> _waiters = new LinkedList<TaskCompletionSource<bool>>();
+        private bool _isSignaled;
 
-        public Task WaitOneAsync(CancellationToken cancellationToken)
+        public AsyncAutoResetEvent() : this(false)
+        { }
+
+        public AsyncAutoResetEvent(bool signaled)
         {
-            return _semaphore.WaitAsync(cancellationToken);
+            _isSignaled = signaled;
+        }
+
+        public Task<bool> WaitOneAsync()
+        {
+            return WaitOneAsync(CancellationToken.None);
+        }
+
+        public Task<bool> WaitOneAsync(TimeSpan timeout)
+        {
+            return WaitOneAsync(timeout, CancellationToken.None);
+        }
+
+        public Task<bool> WaitOneAsync(CancellationToken cancellationToken)
+        {
+            return WaitOneAsync(Timeout.InfiniteTimeSpan, cancellationToken);
+        }
+
+        public async Task<bool> WaitOneAsync(TimeSpan timeout, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            TaskCompletionSource<bool> tcs;
+
+            lock (_waiters)
+            {
+                if (_isSignaled)
+                {
+                    _isSignaled = false;
+                    return true;
+                }
+                else if (timeout == TimeSpan.Zero)
+                {
+                    return _isSignaled;
+                }
+                else
+                {
+                    tcs = new TaskCompletionSource<bool>();
+                    _waiters.AddLast(tcs);
+                }
+            }
+
+            Task winner = await Task.WhenAny(tcs.Task, Task.Delay(timeout, cancellationToken)).ConfigureAwait(false);
+            if (winner == tcs.Task)
+            {
+                // The task was signaled.
+                return true;
+            }
+            else
+            {
+                // We timed-out; remove our reference to the task.
+                // This is an O(n) operation since waiters is a LinkedList<T>.
+                lock (_waiters)
+                {
+                    _waiters.Remove(tcs);
+                    if (winner.Status == TaskStatus.Canceled)
+                    {
+                        throw new OperationCanceledException(cancellationToken);
+                    }
+                    else
+                    {
+                        throw new TimeoutException();
+                    }
+                }
+            }
         }
 
         public void Set()
         {
-            _semaphore.Release();
-        }
+            TaskCompletionSource<bool> toRelease = null;
 
-        public void Dispose()
-        {
-            _semaphore?.Dispose();
+            lock (_waiters)
+            {
+                if (_waiters.Count > 0)
+                {
+                    // Signal the first task in the waiters list.
+                    toRelease = _waiters.First.Value;
+                    _waiters.RemoveFirst();
+                }
+                else if (!_isSignaled)
+                {
+                    // No tasks are pending
+                    _isSignaled = true;
+                }
+            }
+
+            toRelease?.SetResult(true);
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Internal/AsyncLock.cs

@@ -4,23 +4,45 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.Internal
 {
+    // From Stephen Toub (https://blogs.msdn.microsoft.com/pfxteam/2012/02/12/building-async-coordination-primitives-part-6-asynclock/)
     public sealed class AsyncLock : IDisposable
     {
         private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
+        private readonly Task<IDisposable> _releaser;
 
-        public Task EnterAsync(CancellationToken cancellationToken)
+        public AsyncLock()
         {
-            return _semaphore.WaitAsync(cancellationToken);
+            _releaser = Task.FromResult((IDisposable)new Releaser(this));
         }
 
-        public void Exit()
+        public Task<IDisposable> LockAsync(CancellationToken cancellationToken)
         {
-            _semaphore.Release();
+            Task wait = _semaphore.WaitAsync(cancellationToken);
+            return wait.IsCompleted ?
+                        _releaser :
+                        wait.ContinueWith((_, state) => (IDisposable)state,
+                            _releaser.Result, cancellationToken,
+                            TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
         }
 
         public void Dispose()
         {
             _semaphore?.Dispose();
         }
+
+        private sealed class Releaser : IDisposable
+        {
+            private readonly AsyncLock _toRelease;
+
+            internal Releaser(AsyncLock toRelease)
+            {
+                _toRelease = toRelease;
+            }
+
+            public void Dispose()
+            {
+                _toRelease._semaphore.Release();
+            }
+        }
     }
 }

Frameworks/MQTTnet.NetStandard/Server/MqttClientPendingMessagesQueue.cs

@@ -75,7 +75,7 @@ namespace MQTTnet.Server
 
         public void Dispose()
         {
-            _queueAutoResetEvent?.Dispose();
+            
         }
 
         private async Task SendQueuedPacketsAsync(IMqttChannelAdapter adapter, CancellationToken cancellationToken)

Frameworks/MQTTnet.NetStandard/Server/MqttClientSessionsManager.cs

@@ -136,9 +136,9 @@ namespace MQTTnet.Server
             return Task.FromResult((IList<IMqttClientSessionStatus>)result);
         }
 
-        public void StartDispatchApplicationMessage(MqttClientSession senderClientSession, MqttApplicationMessage applicationMessage)
+        public Task StartDispatchApplicationMessage(MqttClientSession senderClientSession, MqttApplicationMessage applicationMessage)
         {
-            Task.Run(() => DispatchApplicationMessageAsync(senderClientSession, applicationMessage));
+            return DispatchApplicationMessageAsync(senderClientSession, applicationMessage);
         }
 
         public Task SubscribeAsync(string clientId, IList<TopicFilter> topicFilters)
@@ -197,8 +197,7 @@ namespace MQTTnet.Server
 
         private async Task<GetOrCreateClientSessionResult> PrepareClientSessionAsync(MqttConnectPacket connectPacket)
         {
-            await _sessionPreparationLock.EnterAsync(CancellationToken.None).ConfigureAwait(false);
-            try
+            using (await _sessionPreparationLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 var isSessionPresent = _sessions.TryGetValue(connectPacket.ClientId, out var clientSession);
                 if (isSessionPresent)
@@ -232,10 +231,6 @@ namespace MQTTnet.Server
 
                 return new GetOrCreateClientSessionResult { IsExistingSession = isExistingSession, Session = clientSession };
             }
-            finally
-            {
-                _sessionPreparationLock.Exit();
-            }
         }
 
         private async Task DispatchApplicationMessageAsync(MqttClientSession senderClientSession, MqttApplicationMessage applicationMessage)

Frameworks/MQTTnet.NetStandard/Server/MqttRetainedMessagesManager.cs

@@ -82,7 +82,7 @@ namespace MQTTnet.Server
         {
             var saveIsRequired = false;
 
-            if (applicationMessage.Payload?.Length > 0)
+            if (applicationMessage.Payload?.Length == 0)
             {
                 saveIsRequired = _messages.TryRemove(applicationMessage.Topic, out _);
                 _logger.Info("Client '{0}' cleared retained message for topic '{1}'.", clientId, applicationMessage.Topic);

Frameworks/MQTTnet.NetStandard/Server/MqttServer.cs

@@ -93,7 +93,7 @@ namespace MQTTnet.Server
             }
 
             _logger.Info("Started.");
-            Started?.Invoke(this, new MqttServerStartedEventArgs());
+            Started?.Invoke(this, EventArgs.Empty);
         }
 
         public async Task StopAsync()
@@ -117,6 +117,7 @@ namespace MQTTnet.Server
                 await _clientSessionsManager.StopAsync().ConfigureAwait(false);
 
                 _logger.Info("Stopped.");
+                Stopped?.Invoke(this, EventArgs.Empty);
             }
             finally
             {

Frameworks/MQTTnet.NetStandard/Server/MqttTopicFilterComparer.cs

@@ -4,46 +4,116 @@ namespace MQTTnet.Server
 {
     public static class MqttTopicFilterComparer
     {
-        private static readonly char[] TopicLevelSeparator = { '/' };
+        private const char LEVEL_SEPARATOR = '/';
+        private const char WILDCARD_MULTI_LEVEL = '#';
+        private const char WILDCARD_SINGLE_LEVEL = '+';
 
         public static bool IsMatch(string topic, string filter)
         {
-            if (topic == null) throw new ArgumentNullException(nameof(topic));
-            if (filter == null) throw new ArgumentNullException(nameof(filter));
+            if (string.IsNullOrEmpty(topic)) throw new ArgumentNullException(nameof(topic));
+            if (string.IsNullOrEmpty(filter)) throw new ArgumentNullException(nameof(filter));
 
-            if (string.Equals(topic, filter, StringComparison.Ordinal))
+            int spos = 0;
+            int slen = filter.Length;
+            int tpos = 0;
+            int tlen = topic.Length;
+
+            while (spos < slen && tpos < tlen)
             {
-                return true;
-            }
-
-            var fragmentsTopic = topic.Split(TopicLevelSeparator, StringSplitOptions.None);
-            var fragmentsFilter = filter.Split(TopicLevelSeparator, StringSplitOptions.None);
-
-            // # > In either case it MUST be the last character specified in the Topic Filter [MQTT-4.7.1-2].
-            for (var i = 0; i < fragmentsFilter.Length; i++)
-            {
-                if (fragmentsFilter[i] == "+")
+                if (filter[spos] == topic[tpos])
                 {
-                    continue;
+                    if (tpos == tlen - 1)
+                    {
+                        /* Check for e.g. foo matching foo/# */
+                        if (spos == slen - 3
+                                && filter[spos + 1] == LEVEL_SEPARATOR
+                                && filter[spos + 2] == WILDCARD_MULTI_LEVEL)
+                        {
+                            return true;
+                        }
+                    }
+                    spos++;
+                    tpos++;
+                    if (spos == slen && tpos == tlen)
+                    {
+                        return true;
+                    }
+                    else if (tpos == tlen && spos == slen - 1 && filter[spos] == WILDCARD_SINGLE_LEVEL)
+                    {
+                        if (spos > 0 && filter[spos - 1] != LEVEL_SEPARATOR)
+                        {
+                            // Invalid filter string
+                            return false;
+                        }
+                        spos++;
+                        return true;
+                    }
                 }
-
-                if (fragmentsFilter[i] == "#")
+                else
                 {
-                    return true;
-                }
-
-                if (i >= fragmentsTopic.Length)
-                {
-                    return false;
-                }
-
-                if (!string.Equals(fragmentsFilter[i], fragmentsTopic[i], StringComparison.Ordinal))
-                {
-                    return false;
+                    if (filter[spos] == WILDCARD_SINGLE_LEVEL)
+                    {
+                        /* Check for bad "+foo" or "a/+foo" subscription */
+                        if (spos > 0 && filter[spos - 1] != LEVEL_SEPARATOR)
+                        {
+                            // Invalid filter string
+                            return false;
+                        }
+                        /* Check for bad "foo+" or "foo+/a" subscription */
+                        if (spos < slen - 1 && filter[spos + 1] != LEVEL_SEPARATOR)
+                        {
+                            // Invalid filter string
+                            return false;
+                        }
+                        spos++;
+                        while (tpos < tlen && topic[tpos] != LEVEL_SEPARATOR)
+                        {
+                            tpos++;
+                        }
+                        if (tpos == tlen && spos == slen)
+                        {
+                            return true;
+                        }
+                    }
+                    else if (filter[spos] == WILDCARD_MULTI_LEVEL)
+                    {
+                        if (spos > 0 && filter[spos - 1] != LEVEL_SEPARATOR)
+                        {
+                            // Invalid filter string
+                            return false;
+                        }
+                        if (spos + 1 != slen)
+                        {
+                            // Invalid filter string
+                            return false;
+                        }
+                        else
+                        {
+                            return true;
+                        }
+                    }
+                    else
+                    {
+                        /* Check for e.g. foo/bar matching foo/+/# */
+                        if (spos > 0
+                                && spos + 2 == slen
+                                && tpos == tlen
+                                && filter[spos - 1] == WILDCARD_SINGLE_LEVEL
+                                && filter[spos] == LEVEL_SEPARATOR
+                                && filter[spos + 1] == WILDCARD_MULTI_LEVEL)
+                        {
+                            return true;
+                        }
+                        return false;
+                    }
                 }
             }
+            if (tpos < tlen || spos < slen)
+            {
+                return false;
+            }
 
-            return fragmentsTopic.Length == fragmentsFilter.Length;
+            return false;
         }
     }
 }

Tests/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -147,6 +147,7 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="TopicFilterComparerBenchmark.cs" />
     <Compile Include="LoggerBenchmark.cs" />
     <Compile Include="MessageProcessingBenchmark.cs" />
     <Compile Include="Program.cs" />

Tests/MQTTnet.Benchmarks/Program.cs

@@ -12,6 +12,7 @@ namespace MQTTnet.Benchmarks
             Console.WriteLine("1 = MessageProcessingBenchmark");
             Console.WriteLine("2 = SerializerBenchmark");
             Console.WriteLine("3 = LoggerBenchmark");
+            Console.WriteLine("4 = TopicFilterComparerBenchmark");
 
             var pressedKey = Console.ReadKey(true);
             switch (pressedKey.KeyChar)
@@ -25,6 +26,9 @@ namespace MQTTnet.Benchmarks
                 case '3':
                     BenchmarkRunner.Run<LoggerBenchmark>();
                     break;
+                case '4':
+                    BenchmarkRunner.Run<TopicFilterComparerBenchmark>();
+                    break;
             }
 
             Console.ReadLine();

Tests/MQTTnet.Benchmarks/TopicFilterComparerBenchmark.cs

@@ -0,0 +1,91 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Attributes.Exporters;
+using BenchmarkDotNet.Attributes.Jobs;
+using MQTTnet.Server;
+using System;
+
+namespace MQTTnet.Benchmarks
+{
+    [ClrJob]
+    [RPlotExporter]
+    [MemoryDiagnoser]
+    public class TopicFilterComparerBenchmark
+    {
+        private static readonly char[] TopicLevelSeparator = { '/' };
+
+        [GlobalSetup]
+        public void Setup()
+        {
+        }
+
+        [Benchmark]
+        public void MqttTopicFilterComparer_10000_StringSplitMethod()
+        {
+            for (var i = 0; i < 10000; i++)
+            {
+                LegacyMethodByStringSplit("sport/tennis/player1", "sport/#");
+                LegacyMethodByStringSplit("sport/tennis/player1/ranking", "sport/#/ranking");
+                LegacyMethodByStringSplit("sport/tennis/player1/score/wimbledon", "sport/+/player1/#");
+                LegacyMethodByStringSplit("sport/tennis/player1", "sport/tennis/+");
+                LegacyMethodByStringSplit("/finance", "+/+");
+                LegacyMethodByStringSplit("/finance", "/+");
+                LegacyMethodByStringSplit("/finance", "+");
+            }
+        }
+
+        [Benchmark]
+        public void MqttTopicFilterComparer_10000_LoopMethod()
+        {
+            for (var i = 0; i < 10000; i++)
+            {
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1", "sport/#");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1/ranking", "sport/#/ranking");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1/score/wimbledon", "sport/+/player1/#");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1", "sport/tennis/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "+/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "+");
+            }
+        }
+
+        private static bool LegacyMethodByStringSplit(string topic, string filter)
+        {
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+            if (filter == null) throw new ArgumentNullException(nameof(filter));
+
+            if (string.Equals(topic, filter, StringComparison.Ordinal))
+            {
+                return true;
+            }
+
+            var fragmentsTopic = topic.Split(TopicLevelSeparator, StringSplitOptions.None);
+            var fragmentsFilter = filter.Split(TopicLevelSeparator, StringSplitOptions.None);
+
+            // # > In either case it MUST be the last character specified in the Topic Filter [MQTT-4.7.1-2].
+            for (var i = 0; i < fragmentsFilter.Length; i++)
+            {
+                if (fragmentsFilter[i] == "+")
+                {
+                    continue;
+                }
+
+                if (fragmentsFilter[i] == "#")
+                {
+                    return true;
+                }
+
+                if (i >= fragmentsTopic.Length)
+                {
+                    return false;
+                }
+
+                if (!string.Equals(fragmentsFilter[i], fragmentsTopic[i], StringComparison.Ordinal))
+                {
+                    return false;
+                }
+            }
+
+            return fragmentsTopic.Length == fragmentsFilter.Length;
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/AsyncAutoResentEventTests.cs

@@ -1,34 +1,210 @@
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Internal;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Core.Tests
 {
     [TestClass]
+    // Inspired from the vs-threading tests (https://github.com/Microsoft/vs-threading/blob/master/src/Microsoft.VisualStudio.Threading.Tests/AsyncAutoResetEventTests.cs)
     public class AsyncAutoResetEventTests
     {
+        private readonly AsyncAutoResetEvent _aare;
+
+        public AsyncAutoResetEventTests()
+        {
+            _aare = new AsyncAutoResetEvent();
+        }
+
+        [TestMethod]
+        public async Task SingleThreadedPulse()
+        {
+            for (int i = 0; i < 5; i++)
+            {
+                var t = _aare.WaitOneAsync();
+                Assert.IsFalse(t.IsCompleted);
+                _aare.Set();
+                await t;
+                Assert.IsTrue(t.IsCompleted);
+            }
+        }
+
+        [TestMethod]
+        public async Task MultipleSetOnlySignalsOnce()
+        {
+            _aare.Set();
+            _aare.Set();
+            await _aare.WaitOneAsync();
+            var t = _aare.WaitOneAsync();
+            Assert.IsFalse(t.IsCompleted);
+            await Task.Delay(500);
+            Assert.IsFalse(t.IsCompleted);
+            _aare.Set();
+            await t;
+            Assert.IsTrue(t.IsCompleted);
+        }
+
+        [TestMethod]
+        public async Task OrderPreservingQueue()
+        {
+            var waiters = new Task[5];
+            for (int i = 0; i < waiters.Length; i++)
+            {
+                waiters[i] = _aare.WaitOneAsync();
+            }
+
+            for (int i = 0; i < waiters.Length; i++)
+            {
+                _aare.Set();
+                await waiters[i].ConfigureAwait(false);
+            }
+        }
+
+        /// <summary>
+        /// Verifies that inlining continuations do not have to complete execution before Set() returns.
+        /// </summary>
+        [TestMethod]
+        public async Task SetReturnsBeforeInlinedContinuations()
+        {
+            var setReturned = new ManualResetEventSlim();
+            var inlinedContinuation = _aare.WaitOneAsync()
+                .ContinueWith(delegate
+                {
+                    // Arrange to synchronously block the continuation until Set() has returned,
+                    // which would deadlock if Set does not return until inlined continuations complete.
+                    Assert.IsTrue(setReturned.Wait(500));
+                });
+            await Task.Delay(100);
+            _aare.Set();
+            setReturned.Set();
+            Assert.IsTrue(inlinedContinuation.Wait(500));
+        }
+
+        [TestMethod]
+        public void WaitAsync_WithCancellationToken()
+        {
+            var cts = new CancellationTokenSource();
+            Task waitTask = _aare.WaitOneAsync(cts.Token);
+            Assert.IsFalse(waitTask.IsCompleted);
+
+            // Cancel the request and ensure that it propagates to the task.
+            cts.Cancel();
+            try
+            {
+                waitTask.GetAwaiter().GetResult();
+                Assert.IsTrue(false, "Task was expected to transition to a canceled state.");
+            }
+            catch (OperationCanceledException ex)
+            {
+                Assert.AreEqual(cts.Token, ex.CancellationToken);
+            }
+
+            // Now set the event and verify that a future waiter gets the signal immediately.
+            _aare.Set();
+            waitTask = _aare.WaitOneAsync();
+            Assert.AreEqual(TaskStatus.RanToCompletion, waitTask.Status);
+        }
+
+        [TestMethod]
+        public void WaitAsync_WithCancellationToken_Precanceled()
+        {
+            // We construct our own pre-canceled token so that we can do
+            // a meaningful identity check later.
+            var tokenSource = new CancellationTokenSource();
+            tokenSource.Cancel();
+            var token = tokenSource.Token;
+
+            // Verify that a pre-set signal is not reset by a canceled wait request.
+            _aare.Set();
+            try
+            {
+                _aare.WaitOneAsync(token).GetAwaiter().GetResult();
+                Assert.IsTrue(false, "Task was expected to transition to a canceled state.");
+            }
+            catch (OperationCanceledException ex)
+            {
+                Assert.AreEqual(token, ex.CancellationToken);
+            }
+
+            // Verify that the signal was not acquired.
+            Task waitTask = _aare.WaitOneAsync();
+            Assert.AreEqual(TaskStatus.RanToCompletion, waitTask.Status);
+        }
+
+        [TestMethod]
+        public async Task WaitAsync_WithTimeout()
+        {
+            Task waitTask = _aare.WaitOneAsync(TimeSpan.FromMilliseconds(500));
+            Assert.IsFalse(waitTask.IsCompleted);
+
+            // Cancel the request and ensure that it propagates to the task.
+            await Task.Delay(1000).ConfigureAwait(false);
+            try
+            {
+                waitTask.GetAwaiter().GetResult();
+                Assert.IsTrue(false, "Task was expected to transition to a timeout state.");
+            }
+            catch (TimeoutException)
+            {
+                Assert.IsTrue(true);
+            }
+
+            // Now set the event and verify that a future waiter gets the signal immediately.
+            _aare.Set();
+            waitTask = _aare.WaitOneAsync(TimeSpan.FromMilliseconds(500));
+            Assert.AreEqual(TaskStatus.RanToCompletion, waitTask.Status);
+        }
+
+        [TestMethod]
+        public void WaitAsync_Canceled_DoesNotInlineContinuations()
+        {
+            var cts = new CancellationTokenSource();
+            var task = _aare.WaitOneAsync(cts.Token);
+
+            var completingActionFinished = new ManualResetEventSlim();
+            var continuation = task.ContinueWith(
+                _ => Assert.IsTrue(completingActionFinished.Wait(500)),
+                CancellationToken.None,
+                TaskContinuationOptions.None,
+                TaskScheduler.Default);
+
+            cts.Cancel();
+            completingActionFinished.Set();
+
+            // Rethrow the exception if it turned out it deadlocked.
+            continuation.GetAwaiter().GetResult();
+        }
+
         [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;
+                globalI += 1;
+            });
+
+#pragma warning disable 4014
+            Task.Run(async () =>
+#pragma warning restore 4014
+            {
+                await aare.WaitOneAsync(CancellationToken.None);
+                globalI += 2;
             });
 
             await Task.Delay(500);
-            increment = 1;
+            aare.Set();
+            await Task.Delay(500);
             aare.Set();
             await Task.Delay(100);
 
-            Assert.AreEqual(1, globalI);
+            Assert.AreEqual(3, globalI);
         }
     }
-}
+}

Tests/MQTTnet.Core.Tests/AsyncLockTests.cs

@@ -21,22 +21,17 @@ namespace MQTTnet.Core.Tests
 #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
+                    using (var releaser = await @lock.LockAsync(CancellationToken.None))
                     {
                         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);
         }