More dangerous gradient builder javadocs

Signed-off-by: Ryan Nett <JNett96@gmail.com>

Author: rnett

tensorflow-core/tensorflow-core-api/src/main/java/org/tensorflow/GraphOperationBuilder.java

@@ -436,6 +436,12 @@ private static TF_OperationDescription allocate(TF_Graph graphHandle, String typ
     return TF_NewOperation(graphHandle, type, name);
   }
 
+  /**
+   * Use builders without locking.  This should only be used during custom gradient building.
+   *
+   * The graph locks are not re-entrant, so attempting to add an op to a graph that has
+   * been locked by the gradient builder will fail without this.
+   */
   private static TF_OperationDescription allocateDangerousGradient(
       TF_Graph graphHandle, String type, String name) {
     if (graphHandle == null || graphHandle.isNull()) {
@@ -455,6 +461,12 @@ private static TF_Operation finish(TF_OperationDescription handle) {
     }
   }
 
+  /**
+   * Use builders without locking.  This should only be used during custom gradient building.
+   *
+   * The graph locks are not re-entrant, so attempting to add an op to a graph that has
+   * been locked by the gradient builder will fail without this.
+   */
   private static TF_Operation finishDangerousGradient(TF_Graph g, TF_OperationDescription handle) {
     requireHandle(handle);