1# Copyright 2015 gRPC authors.
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"""Code for instructing systems under test to block or fail."""
15
16import abc
17import contextlib
18import threading
19
20import six
21
22
23class Defect(Exception):
24    """Simulates a programming defect raised into in a system under test.
25
26  Use of a standard exception type is too easily misconstrued as an actual
27  defect in either the test infrastructure or the system under test.
28  """
29
30
31class Control(six.with_metaclass(abc.ABCMeta)):
32    """An object that accepts program control from a system under test.
33
34  Systems under test passed a Control should call its control() method
35  frequently during execution. The control() method may block, raise an
36  exception, or do nothing, all according to the enclosing test's desire for
37  the system under test to simulate hanging, failing, or functioning.
38  """
39
40    @abc.abstractmethod
41    def control(self):
42        """Potentially does anything."""
43        raise NotImplementedError()
44
45
46class PauseFailControl(Control):
47    """A Control that can be used to pause or fail code under control.
48
49  This object is only safe for use from two threads: one of the system under
50  test calling control and the other from the test system calling pause,
51  block_until_paused, and fail.
52  """
53
54    def __init__(self):
55        self._condition = threading.Condition()
56        self._pause = False
57        self._paused = False
58        self._fail = False
59
60    def control(self):
61        with self._condition:
62            if self._fail:
63                raise Defect()
64
65            while self._pause:
66                self._paused = True
67                self._condition.notify_all()
68                self._condition.wait()
69            self._paused = False
70
71    @contextlib.contextmanager
72    def pause(self):
73        """Pauses code under control while controlling code is in context."""
74        with self._condition:
75            self._pause = True
76        yield
77        with self._condition:
78            self._pause = False
79            self._condition.notify_all()
80
81    def block_until_paused(self):
82        """Blocks controlling code until code under control is paused.
83
84    May only be called within the context of a pause call.
85    """
86        with self._condition:
87            while not self._paused:
88                self._condition.wait()
89
90    @contextlib.contextmanager
91    def fail(self):
92        """Fails code under control while controlling code is in context."""
93        with self._condition:
94            self._fail = True
95        yield
96        with self._condition:
97            self._fail = False
98