1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Utility to get distribution strategy related contexts."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from tensorflow.python.framework import ops
from tensorflow.python.util.lazy_loader import LazyLoader
# There is a circular dependency between this and `distribute` module. So we
# load it lazily to workaround this.
distribute_lib = LazyLoader(
"distribute_lib", globals(),
"tensorflow.python.training.distribute")
# ------------------------------------------------------------------------------
# Internal API for setting the current thread mode as being either in a
# tower or cross-tower context for a particular distribution strategy.
class _ThreadMode(object):
def __init__(self, dist, cross, tower):
self.distribution_strategy = dist
self.cross_tower_context = cross
self.tower_context = tower
class _CrossTowerThreadMode(_ThreadMode):
def __init__(self, distribution_strategy):
_ThreadMode.__init__(
self, distribution_strategy, distribution_strategy, None)
class _InTowerThreadMode(_ThreadMode):
def __init__(self, tower_ctx):
_ThreadMode.__init__(
self, tower_ctx.distribution_strategy, None, tower_ctx)
def _push_per_thread_mode(context):
ops.get_default_graph()._distribution_strategy_stack.append(context) # pylint: disable=protected-access
def _pop_per_thread_mode():
ops.get_default_graph()._distribution_strategy_stack.pop(-1) # pylint: disable=protected-access
class _DefaultTowerThreadMode(_ThreadMode):
"""Type of default value returned by `_get_per_thread_mode()`.
Used when the thread-local stack is empty.
"""
def __init__(self):
_ThreadMode.__init__(self, _get_default_distribution_strategy(), None,
_get_default_tower_context())
def _get_per_thread_mode():
try:
return ops.get_default_graph()._distribution_strategy_stack[-1] # pylint: disable=protected-access
except (AttributeError, IndexError):
return _get_default_tower_mode()
# ------------------------------------------------------------------------------
# Public API for accessing the current thread mode
def get_tower_context():
"""Returns the current TowerContext or None if in a cross-tower context.
Note that execution:
1. starts in the default (single-tower) tower context (this function
will return the default TowerContext object);
2. switches to cross-tower context (in which case this will return
None) when entering a `with DistributionStrategy.scope():` block;
3. switches to a (non-default) tower context inside
`call_for_each_tower(fn, ...)`;
4. if `fn` calls `get_tower_context()->merge_call(merge_fn, ...)`, then
inside `merge_fn` you are back in the cross-tower context (and again
this function will return None).
Note that you can also go directly from step 1 to 4 to switch to a
cross-tower context for the default `DistributionStrategy`. You may
also switch from the cross-tower context of 4 to a tower context by
calling `call_for_each_tower()`, jumping back to step 3.
Most `DistributionStrategy` methods may only be executed in
a cross-tower context, in a tower context you should use the
`TowerContext` API instead.
Returns:
The current `TowerContext` object when in a tower context scope, else None.
Exactly one of `get_tower_context()` and `get_cross_tower_context()`
will return None in a particular block.
"""
return _get_per_thread_mode().tower_context
def get_cross_tower_context():
"""Returns the current DistributionStrategy if in a cross-tower context.
Note that execution:
1. starts in the default (single-tower) tower context;
2. switches to cross-tower context when entering a
`with DistributionStrategy.scope():` block;
3. switches to a (non-default) tower context inside
`call_for_each_tower(fn, ...)`;
4. if `fn` calls `get_tower_context()->merge_call(merge_fn, ...)`, then
inside `merge_fn` you are back in the cross-tower context.
Note that you can also go directly from step 1 to 4 to switch to a
cross-tower context for the default `DistributionStrategy`. You may
also switch from the cross-tower context of 4 to a tower context by
calling `call_for_each_tower()`, jumping back to step 3.
Most `DistributionStrategy` methods may only be executed in
a cross-tower context.
Returns:
Returns the current `DistributionStrategy` object in a cross-tower
context, or None.
Exactly one of `get_tower_context()` and `get_cross_tower_context()`
will return None in a particular block.
"""
return _get_per_thread_mode().cross_tower_context
def get_distribution_strategy():
"""Returns the current `DistributionStrategy` object.
Prefer to use `get_tower_context()` or `get_cross_tower_context()`
instead when possible.
Returns:
A `DistributionStrategy` object. Inside a
`with distribution_strategy.scope()` block, it returns
`distribution_strategy`, otherwise it returns the default
(single-tower) `DistributionStrategy` object.
"""
return _get_per_thread_mode().distribution_strategy
def has_distribution_strategy():
"""Return if there is a current non-default `DistributionStrategy`.
Returns:
True if inside a `with distribution_strategy.scope():`.
"""
return get_distribution_strategy() is not _get_default_distribution_strategy()
# ------------------------------------------------------------------------------
# Defaults that are used when no distribution strategy is explicitly created.
# We create them lazily in a function so that we can workaround the circular
# dependency on distribute_lib. See lazy loader at the top of this file.
_defaults = {
"distribution_strategy": None,
"tower_context": None,
"tower_mode": None
}
def _get_default_distribution_strategy():
if _defaults["distribution_strategy"] is None:
_defaults["distribution_strategy"] = (
distribute_lib._DefaultDistributionStrategy()) # pylint: disable=protected-access
return _defaults["distribution_strategy"]
def _get_default_tower_context():
if _defaults["tower_context"] is None:
_defaults["tower_context"] = distribute_lib.TowerContext(
_get_default_distribution_strategy(), tower_id=0)
return _defaults["tower_context"]
def _get_default_tower_mode():
if _defaults["tower_mode"] is None:
_defaults["tower_mode"] = _DefaultTowerThreadMode()
return _defaults["tower_mode"]
|
