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1# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7#     http://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14# ==============================================================================
15"""Utilities for managing forward accumulators.
16
17A separate file from forwardprop.py so that functions can use these utilities.
18"""
19
20from __future__ import absolute_import
21from __future__ import division
22from __future__ import print_function
23
24import collections
25import contextlib
26
27from tensorflow.python import pywrap_tfe
28
29
30class TangentInfo(
31    collections.namedtuple("TangentInfo", ["indices", "tangents"])):
32  """Packed forward accumulator state. The return value of `pack_tangents`."""
33
34  def __new__(cls, indices=None, tangents=None):
35    if indices is None:
36      indices = ()
37    if tangents is None:
38      tangents = []
39    return super(TangentInfo, cls).__new__(cls, indices, tangents)
40
41
42def pack_tangents(tensors):
43  """Packs forward accumulator state into a TangentInfo tuple.
44
45  Args:
46    tensors: A flat list of Tensors to pack forward accumulator state for.
47
48  Returns:
49    A tuple of (indices, tangents):
50      indices: A sequence of sequences of two-element tuples. Each forward
51        accumulator is represented as a sequence of tuples with (primal_index,
52        jvp_index). Both integers index into the concatenated `tensors + jvps`
53        array.
54      tangents: A flat list of Tensors. Best interpreted as a sequence to be
55        appended to `tensors`.
56  """
57  return TangentInfo(*pywrap_tfe.TFE_Py_PackJVPs(tensors))
58
59
60@contextlib.contextmanager
61def push_forwardprop_state():
62  """Temporarily push or pop transient state for accumulators in the active set.
63
64  Allows an accumulator which is currently processing an operation to
65  temporarily reset its state. This is useful when building forwardprop versions
66  of functions, where an accumulator will trigger function building and then
67  must process captured symbolic tensors while building it. Without pushing and
68  popping, accumulators ignore operations executed as a direct result of their
69  own jvp computations.
70
71  Yields:
72    None (used for its side effect).
73  """
74  try:
75    pywrap_tfe.TFE_Py_ForwardAccumulatorPushState()
76    yield
77  finally:
78    pywrap_tfe.TFE_Py_ForwardAccumulatorPopState()
79