[Modify] Polish it

websocket-sharp/Server/WebSocketSessionManager.cs

@@ -1615,21 +1615,33 @@ namespace WebSocketSharp.Server
     /// </summary>
     public void Sweep ()
     {
-      if (_state != ServerState.Start || _sweeping || Count == 0)
+      if (_sweeping) {
+        _log.Info ("The sweeping is already in progress.");
         return;
+      }
 
       lock (_forSweep) {
+        if (_sweeping) {
+          _log.Info ("The sweeping is already in progress.");
+          return;
+        }
+
         _sweeping = true;
+      }
+
       foreach (var id in InactiveIDs) {
         if (_state != ServerState.Start)
           break;
 
         lock (_sync) {
+          if (_state != ServerState.Start)
+            break;
+
           IWebSocketSession session;
           if (_sessions.TryGetValue (id, out session)) {
             var state = session.State;
             if (state == WebSocketState.Open)
-                session.Context.WebSocket.Close (CloseStatusCode.ProtocolError);
+              session.Context.WebSocket.Close (CloseStatusCode.Abnormal);
             else if (state == WebSocketState.Closing)
               continue;
             else
@@ -1640,7 +1652,6 @@ namespace WebSocketSharp.Server
 
       _sweeping = false;
     }
-    }
 
     /// <summary>
     /// Tries to get the session instance with <paramref name="id"/>.