Implement SignalR.Client's connection state management with thread sa…

…fety in mind.

- Check to make sure we're doing valid state transitions.
- Made State get only and added ChangeSet method which makes sure
  state transitions are valid.
Fixes #474

SignalR.Client/Connection.cs

@@ -5,7 +5,6 @@
 using System.Linq;
 using System.Net;
 using System.Reflection;
-using System.Threading;
 using System.Threading.Tasks;
 using Newtonsoft.Json.Linq;
 using SignalR.Client.Http;
@@ -21,8 +20,12 @@ public class Connection : IConnection
         private static Version _assemblyVersion;
 
         private IClientTransport _transport;
-        private ConnectionState _state;
-        private CancellationTokenSource _cancel;
+
+        // The default connection state is disconnected
+        private ConnectionState _state = ConnectionState.Disconnected;
+
+        // Used to synchornize state changes
+        private readonly object _stateLock = new object();
 
         /// <summary>
         /// Occurs when the <see cref="Connection"/> has received data from the server.
@@ -135,22 +138,17 @@ public Connection(string url, string queryString)
         /// </summary>
         public string QueryString { get; private set; }
 
-        public CancellationToken CancellationToken
-        {
-            get
-            {
-                return _cancel.Token;
-            }
-        }
-
         /// <summary>
         /// Gets the current <see cref="ConnectionState"/> of the connection.
         /// </summary>
         public ConnectionState State
         {
             get
             {
-                return _state;
+                lock (_stateLock)
+                {
+                    return _state;
+                }
             }
             private set
             {
@@ -166,18 +164,6 @@ private set
             }
         }
 
-        ConnectionState IConnection.State
-        {
-            get
-            {
-                return State;
-            }
-            set
-            {
-                State = value;
-            }
-        }
-
         /// <summary>
         /// Starts the <see cref="Connection"/>.
         /// </summary>
@@ -209,15 +195,11 @@ public Task Start(IHttpClient httpClient)
         /// <returns>A task that represents when the connection has started.</returns>
         public virtual Task Start(IClientTransport transport)
         {
-            if (State == ConnectionState.Connected ||
-                State == ConnectionState.Connecting)
+            if (!ChangeState(ConnectionState.Disconnected, ConnectionState.Connecting))
             {
                 return TaskAsyncHelper.Empty;
             }
 
-            State = ConnectionState.Connecting;
-            _cancel = new CancellationTokenSource();
-
             _transport = transport;
 
             return Negotiate(transport);
@@ -271,8 +253,29 @@ private Task Negotiate(IClientTransport transport)
 
         private Task StartTransport(string data)
         {
-            return _transport.Start(this, _cancel.Token, data)
-                             .Then(() => State = ConnectionState.Connected);
+            return _transport.Start(this, data)
+                             .Then(() =>
+                             {
+                                 ChangeState(ConnectionState.Connecting, ConnectionState.Connected);
+                             });
+        }
+
+        private bool ChangeState(ConnectionState oldState, ConnectionState newState)
+        {
+            return ((IConnection)this).ChangeState(oldState, newState);
+        }
+
+        bool IConnection.ChangeState(ConnectionState oldState, ConnectionState newState)
+        {
+            lock (_stateLock)
+            {
+                if (_state == oldState)
+                {
+                    State = newState;
+                    return true;
+                }
+                return false;
+            }
         }
 
         private static void VerifyProtocolVersion(string versionString)
@@ -294,14 +297,11 @@ public virtual void Stop()
             try
             {
                 // Do nothing if the connection is offline
-                if (this.IsDisconnecting())
+                if (State == ConnectionState.Disconnected)
                 {
                     return;
                 }
 
-                State = ConnectionState.Disconnecting;
-
-                _cancel.Cancel(throwOnFirstException: false);
                 _transport.Stop(this);
 
                 if (Closed != null)
@@ -327,7 +327,7 @@ public Task Send(string data)
 
         Task<T> IConnection.Send<T>(string data)
         {
-            if (this.IsDisconnecting())
+            if (State == ConnectionState.Disconnected)
             {
                 // TODO: Update this error message
                 throw new InvalidOperationException("Start must be called before data can be sent");

SignalR.Client/ConnectionExtensions.cs

@@ -16,18 +16,6 @@ public static T GetValue<T>(this IConnection connection, string key)
             return default(T);
         }
 
-        public static bool IsDisconnecting(this IConnection connection)
-        {
-            return connection.State == ConnectionState.Disconnecting ||
-                   connection.State == ConnectionState.Disconnected;
-        }
-
-        public static bool IsActive(this IConnection connection)
-        {
-            return connection.State == ConnectionState.Connected ||
-                   connection.State == ConnectionState.Connecting;
-        }
-
 #if !WINDOWS_PHONE && !SILVERLIGHT && !NET35
         public static IObservable<string> AsObservable(this Connection connection)
         {

SignalR.Client/ConnectionState.cs

@@ -5,7 +5,6 @@ public enum ConnectionState
         Connecting,
         Connected,
         Reconnecting,
-        Disconnecting,
         Disconnected
     }
 }

SignalR.Client/IConnection.cs

@@ -16,7 +16,9 @@ public interface IConnection
         string ConnectionId { get; }
         string Url { get; }
         string QueryString { get; }
-        ConnectionState State { get; set; }
+        ConnectionState State { get; }
+
+        bool ChangeState(ConnectionState oldState, ConnectionState newState);
 
         ICredentials Credentials { get; set; }
         CookieContainer CookieContainer { get; set; }

SignalR.Client/Transports/AutoTransport.cs

@@ -26,22 +26,22 @@ public Task<NegotiationResponse> Negotiate(IConnection connection)
             return HttpBasedTransport.GetNegotiationResponse(_httpClient, connection);
         }
 
-        public Task Start(IConnection connection, CancellationToken cancellationToken, string data)
+        public Task Start(IConnection connection, string data)
         {
             var tcs = new TaskCompletionSource<object>();
 
             // Resolve the transport
-            ResolveTransport(connection, cancellationToken, data, tcs, 0);
+            ResolveTransport(connection, data, tcs, 0);
 
             return tcs.Task;
         }
 
-        private void ResolveTransport(IConnection connection, CancellationToken cancellationToken, string data, TaskCompletionSource<object> tcs, int index)
+        private void ResolveTransport(IConnection connection, string data, TaskCompletionSource<object> tcs, int index)
         {
             // Pick the current transport
             IClientTransport transport = _transports[index];
 
-            transport.Start(connection, cancellationToken, data).ContinueWith(task =>
+            transport.Start(connection, data).ContinueWith(task =>
             {
                 if (task.IsFaulted)
                 {
@@ -61,7 +61,7 @@ private void ResolveTransport(IConnection connection, CancellationToken cancella
                     if (next < _transports.Length)
                     {
                         // Try the next transport
-                        ResolveTransport(connection, cancellationToken, data, tcs, next);
+                        ResolveTransport(connection, data, tcs, next);
                     }
                     else
                     {