ConnectionState: Add thread safety with atomic updates (#284)

Author: pglombardo

Source/HiveMQtt/Client/Connection/ConnectionManager.cs

@@ -44,8 +44,18 @@ public partial class ConnectionManager : IDisposable
     // This is how we kill innocent and not so innocent Tasks
     private CancellationTokenSource cancellationTokenSource;
 
-    // The state of the connection
-    internal ConnectState State { get; set; }
+    // The state of the connection (thread-safe using Interlocked)
+    private int stateValue = (int)ConnectState.Disconnected;
+
+    /// <summary>
+    /// Gets or sets the connection state in a thread-safe manner.
+    /// Uses Volatile.Read for reads and Interlocked.Exchange for writes to ensure thread safety.
+    /// </summary>
+    internal ConnectState State
+    {
+        get => (ConnectState)Volatile.Read(ref this.stateValue);
+        set => Interlocked.Exchange(ref this.stateValue, (int)value);
+    }
 
     // The protocol specific transport layer (TCP, WebSocket, etc.)
     internal BaseTransport Transport { get; set; }

Source/HiveMQtt/Client/Connection/ConnectionManagerHandlers.cs

@@ -380,6 +380,7 @@ internal async Task HandleIncomingPubCompPacketAsync(PubCompPacket pubCompPacket
     /// <returns>A task that represents the asynchronous operation.</returns>
     internal async Task<bool> HandleDisconnectionAsync(bool clean = true)
     {
+        // Thread-safe check: if already disconnected, return early
         if (this.State == ConnectState.Disconnected)
         {
             Logger.Trace("HandleDisconnection: Already disconnected.");
@@ -388,18 +389,20 @@ internal async Task<bool> HandleDisconnectionAsync(bool clean = true)
 
         Logger.Debug($"HandleDisconnection: Handling disconnection. clean={clean}.");
 
-        // Cancel all background tasks and close the socket
-        this.State = ConnectState.Disconnected;
-
         // Reset the connection-ready signal for the next connect cycle
         this.ResetConnectedSignal();
 
-        // Cancel all background tasks
+        // Cancel all background tasks BEFORE setting state to Disconnected
+        // This prevents race conditions where tasks check state after it's set but before cancellation
         await this.CancelBackgroundTasksAsync().ConfigureAwait(false);
 
         // Close the Transport
         await this.Transport.CloseAsync().ConfigureAwait(false);
 
+        // Set state to Disconnected AFTER tasks are cancelled and transport is closed
+        // This ensures tasks see the correct state when they check during cancellation
+        this.State = ConnectState.Disconnected;
+
         if (clean)
         {
             if (!this.SendQueue.IsEmpty)