add DefaultGraphStack

Author: alexpantyukhin

TensorFlowSharp/Tensorflow.cs

@@ -108,6 +108,36 @@ internal static void CheckSize ()
 		}
 	}
 
+	internal class DefaultGraphStack
+	{
+		[ThreadStatic]
+		private static IList<TFGraph> stack;
+		private static Object lockObj;
+
+		internal TFGraph Instance => stack.Last();
+
+		internal static void SetGraph(TFGraph graph)
+		{
+			if (stack == null)
+			{
+				lock (lockObj)
+				{
+					if (stack == null)
+					{
+						stack = new List<TFGraph>();
+					}
+				}
+			}
+
+			stack.Add(graph);
+		}
+
+		internal static void RemoveGraph(TFGraph graph)
+		{
+			stack.Remove(graph);
+		}
+	}
+
 	/// <summary>
 	/// Base class for many TensorFlow data types that provides a common idiom to dispose and
 	/// release resources associated with the native data types.   Generally, you do not need to use this.
@@ -479,13 +509,15 @@ public TFGraph () : base (TF_NewGraph ())
 
 		internal TFGraph (IntPtr handle) : base (handle)
 		{
+			DefaultGraphStack.SetGraph(this);
 		}
 
 		// extern void TF_DeleteGraph (TF_Graph *);
 		[DllImport (NativeBinding.TensorFlowLibrary)]
 		static extern unsafe void TF_DeleteGraph (TF_Graph graph);
 		internal override void NativeDispose (IntPtr handle)
 		{
+			DefaultGraphStack.RemoveGraph(this);
 			TF_DeleteGraph (handle);
 		}