From 2300e619aaab8bd7b7203d1004ca81b922243d14 Mon Sep 17 00:00:00 2001
From: Oceania2018 <haiping008@gmail.com>
Date: Fri, 21 Dec 2018 07:28:06 -0600
Subject: [PATCH] _FetchHandler

---
 src/TensorFlowNET.Core/Graph.cs               | 15 +++++++++++
 .../Session/_ElementFetchMapper.cs            |  5 ++++
 .../Session/_FetchHandler.cs                  | 25 +++++++++++++++++++
 3 files changed, 45 insertions(+)

diff --git a/src/TensorFlowNET.Core/Graph.cs b/src/TensorFlowNET.Core/Graph.cs
index 6a447463..96131b8a 100644
--- a/src/TensorFlowNET.Core/Graph.cs
+++ b/src/TensorFlowNET.Core/Graph.cs
@@ -22,6 +22,7 @@ namespace Tensorflow
         private Dictionary<string, int> _names_in_use;
         public int _version;
         private int _next_id_counter;
+        private List<String> _unfetchable_ops = new List<string>();
 
         public Graph(IntPtr graph)
         {
@@ -111,6 +112,20 @@ namespace Tensorflow
             return ++_next_id_counter;
         }
 
+        public bool is_fetchable<T>(T tensor_or_op)
+        {
+            if (tensor_or_op is Tensor)
+            {
+                return !_unfetchable_ops.Contains((tensor_or_op as Tensor).name); ;
+            }
+            else if (tensor_or_op is Operation)
+            {
+                return !_unfetchable_ops.Contains((tensor_or_op as Operation).name);
+            }
+
+            return false;
+        }
+
         public string unique_name(string name)
         {
             var name_key = name.ToLower();
diff --git a/src/TensorFlowNET.Core/Session/_ElementFetchMapper.cs b/src/TensorFlowNET.Core/Session/_ElementFetchMapper.cs
index 310b1cfc..94565316 100644
--- a/src/TensorFlowNET.Core/Session/_ElementFetchMapper.cs
+++ b/src/TensorFlowNET.Core/Session/_ElementFetchMapper.cs
@@ -20,5 +20,10 @@ namespace Tensorflow
                 _unique_fetches.Add(fetch);
             }
         }
+
+        public List<Object> unique_fetches()
+        {
+            return _unique_fetches;
+        }
     }
 }
diff --git a/src/TensorFlowNET.Core/Session/_FetchHandler.cs b/src/TensorFlowNET.Core/Session/_FetchHandler.cs
index 35b5e4b6..eb14ef69 100644
--- a/src/TensorFlowNET.Core/Session/_FetchHandler.cs
+++ b/src/TensorFlowNET.Core/Session/_FetchHandler.cs
@@ -10,10 +10,35 @@ namespace Tensorflow
     public class _FetchHandler
     {
         private _ElementFetchMapper _fetch_mapper;
+        private List<object> _fetches = new List<object>();
+        private List<bool> _ops = new List<bool>();
+        private List<object> _final_fetches = new List<object>();
 
         public _FetchHandler(Graph graph, Tensor fetches, object feeds = null, object feed_handles = null)
         {
             _fetch_mapper = new _FetchMapper().for_fetch(fetches);
+            foreach(var fetch in _fetch_mapper.unique_fetches())
+            {
+                switch (fetch)
+                {
+                    case Tensor val:
+                        _assert_fetchable(graph, val.op);
+                        _fetches.Add(fetch);
+                        _ops.Add(false);
+                        break;
+                }
+
+            }
+
+            _final_fetches = _fetches;
+        }
+
+        private void _assert_fetchable(Graph graph, Operation op)
+        {
+            if (!graph.is_fetchable(op))
+            {
+                throw new Exception($"Operation {op.name} has been marked as not fetchable.");
+            }
         }
     }
 }