diff --git a/src/TensorFlowNET.Core/Operations/ControlFlows/GradLoopState.cs b/src/TensorFlowNET.Core/Operations/ControlFlows/GradLoopState.cs
index 143aacb1..2552df8a 100644
--- a/src/TensorFlowNET.Core/Operations/ControlFlows/GradLoopState.cs
+++ b/src/TensorFlowNET.Core/Operations/ControlFlows/GradLoopState.cs
@@ -78,6 +78,26 @@ namespace Tensorflow.Operations.ControlFlows
         /// </summary>
         public int pending_exits_count { get; set; }
 
+        Operation _grad_sync;
+        public Operation grad_sync
+        {
+            get
+            {
+                if(_grad_sync == null)
+                {
+                    tf_with(ops.control_dependencies(null), delegate
+                    {
+                        _grad_sync = gen_control_flow_ops.control_trigger(name: "b_sync");
+                    });
+                    _grad_sync._set_control_flow_context(_grad_context);
+                    _grad_index.op._add_control_input(_grad_sync);
+                    if (_grad_context.outer_context != null)
+                        _grad_context.outer_context.AddInnerOp(_grad_sync);
+                }
+                return _grad_sync;
+            }
+        }
+
         public GradLoopState(WhileContext forward_ctxt, GradLoopState outer_grad_state_)
         {
             // Information needed by backprop.
@@ -155,7 +175,7 @@ namespace Tensorflow.Operations.ControlFlows
         /// <returns>The stack that contains the accumulated history of the tensor.</returns>
         public Tensor AddForwardAccumulator(Tensor value, bool dead_branch = false)
         {
-            using (_forward_index.graph.as_default())
+            _forward_index.graph.as_default();
             {
                 var curr_ctxt = ops.get_default_graph()._get_control_flow_context();
                 return tf_with(ops.control_dependencies(null), delegate
@@ -220,38 +240,33 @@ namespace Tensorflow.Operations.ControlFlows
 
         public Tensor AddBackpropAccumulatedValue(Tensor history_value, Tensor value, bool dead_branch= false)
         {
-            throw new NotImplementedException();
-            //    history_ctxt = history_value.op._get_control_flow_context()
-            //    # Find the cond context that controls history_value if any.
-            //    cond_ctxt = None
-            //    value_ctxt = value.op._get_control_flow_context()
-            //    while value_ctxt and value_ctxt != history_ctxt:
-            //      if isinstance(value_ctxt, CondContext):
-            //        cond_ctxt = value_ctxt
-            //        break
-            //      value_ctxt = value_ctxt.outer_context
-            //    with ops.control_dependencies(None):
-            //      self.grad_context.Enter()
-            //      if cond_ctxt:
-            //        # Guard stack pop with a switch if it is controlled by a cond.
-            //        grad_state = self
-            //        pred = None
-            //        while pred is None and grad_state:
-            //          pred = grad_state.history_map.get(cond_ctxt.pred.name)
-            //          grad_state = grad_state.outer_grad_state
-            //        if pred is None:
-            //          pred = cond_ctxt.pred
-            //        branch = (1 - cond_ctxt.branch) if dead_branch else cond_ctxt.branch
-            //        history_value = _SwitchRefOrTensor(history_value, pred)[branch]
-            //      pop = gen_data_flow_ops.stack_pop_v2(history_value,
-            //                                           value.dtype.base_dtype)
-            //      pop.set_shape(value.get_shape())
-            //      self.grad_context.Exit()
-            //    parallel_iterations = self.grad_context.parallel_iterations
-            //    if parallel_iterations > 1:
-            //      # All pops are ordered after pivot_for_body and before grad_sync.
-            //      self.grad_sync._add_control_input(pop.op)
-            //    return pop
+            var history_ctxt = history_value.op._get_control_flow_context();
+            // Find the cond context that controls history_value if any.
+            CondContext cond_ctxt = null;
+            Tensor pop = null;
+            var value_ctxt = value.op._get_control_flow_context();
+            while(value_ctxt != null && value_ctxt != history_ctxt)
+            {
+                if (value_ctxt is CondContext cc)
+                    cond_ctxt = cc;
+                value_ctxt = value_ctxt.outer_context;
+            }
+            tf_with(ops.control_dependencies(null), delegate
+            {
+                grad_context.Enter();
+                if(cond_ctxt != null)
+                {
+                    throw new NotImplementedException("AddBackpropAccumulatedValue");
+                }
+                pop = gen_data_flow_ops.stack_pop_v2(history_value, value.dtype.as_base_dtype());
+                pop.set_shape(value.TensorShape);
+                grad_context.Exit();
+            });
+            var parallel_iterations = grad_context.parallel_iterations;
+            if (parallel_iterations > 1)
+                // All pops are ordered after pivot_for_body and before grad_sync.
+                grad_sync._add_control_input(pop.op);
+            return pop;
         }
 
         /// <summary>
@@ -272,11 +287,28 @@ namespace Tensorflow.Operations.ControlFlows
                     var enter_op = util.GetLoopConstantEnter(cur_value);
                     if(enter_op != null)
                     {
-                        throw new NotImplementedException("GetRealValue");
+                        // Special case: cur_value comes from a constant Enter node.
+                        cur_value = enter_op.inputs[0];
+                        cur_grad_state = cur_grad_state.outer_grad_state;
+                        if(cur_grad_state == null)
+                        {
+                            // We are now outside all nested loops for this gradient(),
+                            // so `value` is a loop invariant and there is no need to
+                            // save the history of value. Just make cur_value to enter
+                            // the right control flow context.
+                            real_value = _grad_context.AddValue(cur_value);
+                            break;
+                        }
                     }
                     else if (constant_op.is_constant(cur_value))
                     {
-                        throw new NotImplementedException("GetRealValue");
+                        // We are now outside all nested loops for this gradient(),
+                        // so `value` is a loop invariant and there is no need to
+                        // save the history of value. Just make cur_value to enter
+                        // the right control flow context.
+                        real_value = constant_op.constant(
+                            tensor_util.constant_value(cur_value), dtype: cur_value.dtype);
+                        break;
                     }
                     else
                     {