Replace a manual lock with the lock class.

Frameworks/MQTTnet.NetStandard/ManagedClient/ManagedMqttClient.cs

@@ -7,6 +7,7 @@ using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.ManagedClient
@@ -15,7 +16,7 @@ namespace MQTTnet.ManagedClient
     {
         private readonly BlockingCollection<MqttApplicationMessage> _messageQueue = new BlockingCollection<MqttApplicationMessage>();
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
-        private readonly SemaphoreSlim _subscriptionsSemaphore = new SemaphoreSlim(1, 1);
+        private readonly AsyncLock _subscriptionsLock = new AsyncLock();
         private readonly List<string> _unsubscriptions = new List<string>();
 
         private readonly IMqttClient _mqttClient;
@@ -117,8 +118,7 @@ namespace MQTTnet.ManagedClient
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            await _subscriptionsSemaphore.WaitAsync().ConfigureAwait(false);
-            try
+            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 foreach (var topicFilter in topicFilters)
                 {
@@ -126,16 +126,11 @@ namespace MQTTnet.ManagedClient
                     _subscriptionsNotPushed = true;
                 }
             }
-            finally
-            {
-                _subscriptionsSemaphore.Release();
-            }
         }
 
         public async Task UnsubscribeAsync(IEnumerable<string> topics)
         {
-            await _subscriptionsSemaphore.WaitAsync().ConfigureAwait(false);
-            try
+            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 foreach (var topic in topics)
                 {
@@ -146,16 +141,12 @@ namespace MQTTnet.ManagedClient
                     }
                 }
             }
-            finally
-            {
-                _subscriptionsSemaphore.Release();
-            }
         }
 
         public void Dispose()
         {
             _messageQueue?.Dispose();
-            _subscriptionsSemaphore?.Dispose();
+            _subscriptionsLock?.Dispose();
             _connectionCancellationToken?.Dispose();
             _publishingCancellationToken?.Dispose();
         }
@@ -294,8 +285,7 @@ namespace MQTTnet.ManagedClient
             List<TopicFilter> subscriptions;
             List<string> unsubscriptions;
 
-            await _subscriptionsSemaphore.WaitAsync().ConfigureAwait(false);
-            try
+            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 subscriptions = _subscriptions.Select(i => new TopicFilter(i.Key, i.Value)).ToList();
 
@@ -304,10 +294,6 @@ namespace MQTTnet.ManagedClient
 
                 _subscriptionsNotPushed = false;
             }
-            finally
-            {
-                _subscriptionsSemaphore.Release();
-            }
             
             if (!subscriptions.Any() && !unsubscriptions.Any())
             {