In `assign_moving_average`, call `update_fn` instead of `strategy.extended.update(var, update_fn)` when in update context.

This fixes an issue where variables may be updated #num_replica times when `assign_moving_average` is called in update context. See the unit test for an example.

PiperOrigin-RevId: 315804133
Change-Id: If4b31ef15fcf5d1bb93ec53fa6ff6c234a13626a

tensorflow/python/distribute/moving_averages_test.py

@@ -149,6 +149,24 @@ class AssignMovingAveragesTest(test.TestCase, parameterized.TestCase):
            (2.0 * 0.25 + 0.0) / (1.0 * 0.25 + 1.0)],
           var.eval())
 
+  @combinations.generate(all_combinations_eager)
+  def testUpdateContext(self, distribution, use_function):
+    with distribution.scope():
+      var1 = variables.Variable([0.0, 0.0])
+      var2 = variables.Variable([0.0, 0.0])
+      var3 = variables.Variable([0.0, 0.0])
+
+      def update_fn(v, value):
+        v.assign_add(value)
+        moving_averages.assign_moving_average(var2, [2.0, 4.0], decay=0.25)
+        moving_averages.assign_moving_average(
+            var3, [2.0, 4.0], decay=0.25, zero_debias=False)
+
+      distribution.extended.update(var1, update_fn, ([1.0, 1.0],))
+
+      self.assertAllClose([2.0, 4.0], var2.read_value())
+      self.assertAllClose([1.5, 3.0], var3.read_value())
+
   @combinations.generate(all_combinations)
   def testAssignVariable(self, distribution):
 

tensorflow/python/training/moving_averages.py

@@ -17,6 +17,7 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
+from tensorflow.python.distribute import distribute_lib
 from tensorflow.python.distribute import distribution_strategy_context
 from tensorflow.python.distribute import reduce_util as ds_reduce_util
 from tensorflow.python.framework import dtypes
@@ -83,7 +84,6 @@ def assign_moving_average(variable, value, decay, zero_debias=True, name=None):
       [Kingma et al., 2015](https://arxiv.org/abs/1412.6980)
       ([pdf](https://arxiv.org/pdf/1412.6980.pdf))
   """
-
   with ops.name_scope(name, "AssignMovingAvg",
                       [variable, value, decay]) as scope:
     decay = ops.convert_to_tensor(1.0 - decay, name="decay")
@@ -97,7 +97,7 @@ def assign_moving_average(variable, value, decay, zero_debias=True, name=None):
       if zero_debias:
         return _zero_debias(strategy, v, value, decay)
       else:
-        return strategy.extended.update(v, update_fn, args=(value,))
+        return _update(strategy, v, update_fn, args=(value,))
 
     replica_context = distribution_strategy_context.get_replica_context()
     if replica_context:
@@ -178,6 +178,20 @@ def weighted_moving_average(value,
       return math_ops.divide(numerator, denominator, name=scope.name)
 
 
+def _update(strategy, var, update_fn, args):
+  """Applies updates depending on the context."""
+  assert distribution_strategy_context.in_cross_replica_context(), (
+      "_update can only be called in cross-replica context")
+  if distribute_lib.get_update_replica_id() is not None:
+    # Call update_fn on var to delegate the implementation. We expect `var` will
+    # do the right thing in update context, e.g, if `var` is a MirroredVariable,
+    # it should pick its component variable based on `update_replica_id` and
+    # only update that.
+    return update_fn(var, *args)
+  else:
+    return strategy.extended.update(var, update_fn, args)
+
+
 def _zero_debias(strategy, unbiased_var, value, decay):
   """Compute the delta required for a debiased Variable.
 
@@ -263,8 +277,8 @@ def _zero_debias(strategy, unbiased_var, value, decay):
     return state_ops.assign(
         v, update_biased / bias_factor, name=ops.get_name_scope() + "/")
 
-  return strategy.extended.update(
+  return _update(
-      unbiased_var, update_fn, args=(value, biased_var, local_step))
+      strategy, unbiased_var, update_fn, args=(value, biased_var, local_step))
 
 
 @tf_export("train.ExponentialMovingAverage")