message: Editing IteratorStateReader and IteratorStateWriter documentation to indicate their thread safeness.
diff: @@ -70,7 +70,7 @@ class DatasetBase;
  class SerializationContext;
  // Interface for reading values from a key-value store.
  -// Used for restoring iterator state.
  +// Used for restoring iterator state. This class is thread safe.
  // Please see comment on IteratorStateWriter for guidance around using the
  // Read*(key, val) vs Read*(name, key, val).
  class IteratorStateReader {
  @@ -91,7 +91,7 @@ class IteratorStateReader {
  };
  // Interface for writing values to a key-value store.
  -// Used for saving iterator state.
  +// Used for saving iterator state. Not thread safe.
  // The IteratorStateWriter creates a tensor for each unique iterator name it
  // sees. For the Write*(key, val) API's the key is expected to encode this
  // name as keys are required to be produced using the full_name() method.
  