message: This is a bug fix for multi-replica training. When there is any parameter servers and more than one replica, replicas except the chief replica would complain un-initialized stale_counter variable since it doesn't live in parameter server.
diff: @@ -78,6 +78,7 @@ class DropStaleGradientOptimizer(optimizer.Optimizer):
  def apply_gradients(self, grads_and_vars, global_step=None, name=None):
  gradients = []
  # Number of stale gradients.
  + with ops.colocate_with(global_step):
  stale_counter = variable_scope.get_variable(
  "stale_counter", [],
  initializer=init_ops.zeros_initializer(),
  