Fix possible multithreading issue

Author: nvoronchev

src/Bus.cs

@@ -59,11 +59,13 @@ public static Bus Starter
 				throw new ArgumentNullException ("address");
 
 			Bus bus;
-			if (buses.TryGetValue (address, out bus))
-				return bus;
+			lock (buses) {
+				if (buses.TryGetValue (address, out bus))
+					return bus;
 
-			bus = new Bus (address);
-			buses[address] = bus;
+				bus = new Bus (address);
+				buses[address] = bus;
+			}
 
 			return bus;
 		}

src/ExportObject.cs

@@ -67,9 +67,11 @@ internal virtual void WriteIntrospect (Introspector intro)
 		internal static MethodCaller GetMCaller (MethodInfo mi)
 		{
 			MethodCaller mCaller;
-			if (!mCallers.TryGetValue (mi, out mCaller)) {
-				mCaller = TypeImplementer.GenCaller (mi);
-				mCallers[mi] = mCaller;
+			lock (mCallers) {
+				if (!mCallers.TryGetValue (mi, out mCaller)) {
+					mCaller = TypeImplementer.GenCaller (mi);
+					mCallers[mi] = mCaller;
+				}
 			}
 			return mCaller;
 		}
@@ -90,11 +92,7 @@ public virtual void HandleMethodCall (MessageContainer method_call)
 				return;
 			}
 
-			MethodCaller mCaller;
-			if (!mCallers.TryGetValue (mi, out mCaller)) {
-				mCaller = TypeImplementer.GenCaller (mi);
-				mCallers[mi] = mCaller;
-			}
+			MethodCaller mCaller = GetMCaller (mi);
 
 			Signature inSig, outSig;
 			bool hasDisposableList;