summaryrefslogtreecommitdiffstats
path: root/Lib/test/test_finalization.py
blob: 80c9b87988781babe8088370b4cc8fd9d5363ce1 (plain)
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
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
"""
Tests for object finalization semantics, as outlined in PEP 442.
"""

import contextlib
import gc
import unittest
import weakref

import _testcapi
from test import support


class NonGCSimpleBase:
    """
    The base class for all the objects under test, equipped with various
    testing features.
    """

    survivors = []
    del_calls = []
    tp_del_calls = []
    errors = []

    _cleaning = False

    __slots__ = ()

    @classmethod
    def _cleanup(cls):
        cls.survivors.clear()
        cls.errors.clear()
        gc.garbage.clear()
        gc.collect()
        cls.del_calls.clear()
        cls.tp_del_calls.clear()

    @classmethod
    @contextlib.contextmanager
    def test(cls):
        """
        A context manager to use around all finalization tests.
        """
        with support.disable_gc():
            cls.del_calls.clear()
            cls.tp_del_calls.clear()
            NonGCSimpleBase._cleaning = False
            try:
                yield
                if cls.errors:
                    raise cls.errors[0]
            finally:
                NonGCSimpleBase._cleaning = True
                cls._cleanup()

    def check_sanity(self):
        """
        Check the object is sane (non-broken).
        """

    def __del__(self):
        """
        PEP 442 finalizer.  Record that this was called, check the
        object is in a sane state, and invoke a side effect.
        """
        try:
            if not self._cleaning:
                self.del_calls.append(id(self))
                self.check_sanity()
                self.side_effect()
        except Exception as e:
            self.errors.append(e)

    def side_effect(self):
        """
        A side effect called on destruction.
        """


class SimpleBase(NonGCSimpleBase):

    def __init__(self):
        self.id_ = id(self)

    def check_sanity(self):
        assert self.id_ == id(self)


class NonGC(NonGCSimpleBase):
    __slots__ = ()

class NonGCResurrector(NonGCSimpleBase):
    __slots__ = ()

    def side_effect(self):
        """
        Resurrect self by storing self in a class-wide list.
        """
        self.survivors.append(self)

class Simple(SimpleBase):
    pass

class SimpleResurrector(NonGCResurrector, SimpleBase):
    pass


class TestBase:

    def setUp(self):
        self.old_garbage = gc.garbage[:]
        gc.garbage[:] = []

    def tearDown(self):
        # None of the tests here should put anything in gc.garbage
        try:
            self.assertEqual(gc.garbage, [])
        finally:
            del self.old_garbage
            gc.collect()

    def assert_del_calls(self, ids):
        self.assertEqual(sorted(SimpleBase.del_calls), sorted(ids))

    def assert_tp_del_calls(self, ids):
        self.assertEqual(sorted(SimpleBase.tp_del_calls), sorted(ids))

    def assert_survivors(self, ids):
        self.assertEqual(sorted(id(x) for x in SimpleBase.survivors), sorted(ids))

    def assert_garbage(self, ids):
        self.assertEqual(sorted(id(x) for x in gc.garbage), sorted(ids))

    def clear_survivors(self):
        SimpleBase.survivors.clear()


class SimpleFinalizationTest(TestBase, unittest.TestCase):
    """
    Test finalization without refcycles.
    """

    def test_simple(self):
        with SimpleBase.test():
            s = Simple()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])

    def test_simple_resurrect(self):
        with SimpleBase.test():
            s = SimpleResurrector()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors(ids)
            self.assertIsNot(wr(), None)
            self.clear_survivors()
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
        self.assertIs(wr(), None)

    def test_non_gc(self):
        with SimpleBase.test():
            s = NonGC()
            self.assertFalse(gc.is_tracked(s))
            ids = [id(s)]
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])

    def test_non_gc_resurrect(self):
        with SimpleBase.test():
            s = NonGCResurrector()
            self.assertFalse(gc.is_tracked(s))
            ids = [id(s)]
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors(ids)
            self.clear_survivors()
            gc.collect()
            self.assert_del_calls(ids * 2)
            self.assert_survivors(ids)


class SelfCycleBase:

    def __init__(self):
        super().__init__()
        self.ref = self

    def check_sanity(self):
        super().check_sanity()
        assert self.ref is self

class SimpleSelfCycle(SelfCycleBase, Simple):
    pass

class SelfCycleResurrector(SelfCycleBase, SimpleResurrector):
    pass

class SuicidalSelfCycle(SelfCycleBase, Simple):

    def side_effect(self):
        """
        Explicitly break the reference cycle.
        """
        self.ref = None


class SelfCycleFinalizationTest(TestBase, unittest.TestCase):
    """
    Test finalization of an object having a single cyclic reference to
    itself.
    """

    def test_simple(self):
        with SimpleBase.test():
            s = SimpleSelfCycle()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])

    def test_simple_resurrect(self):
        # Test that __del__ can resurrect the object being finalized.
        with SimpleBase.test():
            s = SelfCycleResurrector()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors(ids)
            # XXX is this desirable?
            self.assertIs(wr(), None)
            # When trying to destroy the object a second time, __del__
            # isn't called anymore (and the object isn't resurrected).
            self.clear_survivors()
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)

    def test_simple_suicide(self):
        # Test the GC is able to deal with an object that kills its last
        # reference during __del__.
        with SimpleBase.test():
            s = SuicidalSelfCycle()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)


class ChainedBase:

    def chain(self, left):
        self.suicided = False
        self.left = left
        left.right = self

    def check_sanity(self):
        super().check_sanity()
        if self.suicided:
            assert self.left is None
            assert self.right is None
        else:
            left = self.left
            if left.suicided:
                assert left.right is None
            else:
                assert left.right is self
            right = self.right
            if right.suicided:
                assert right.left is None
            else:
                assert right.left is self

class SimpleChained(ChainedBase, Simple):
    pass

class ChainedResurrector(ChainedBase, SimpleResurrector):
    pass

class SuicidalChained(ChainedBase, Simple):

    def side_effect(self):
        """
        Explicitly break the reference cycle.
        """
        self.suicided = True
        self.left = None
        self.right = None


class CycleChainFinalizationTest(TestBase, unittest.TestCase):
    """
    Test finalization of a cyclic chain.  These tests are similar in
    spirit to the self-cycle tests above, but the collectable object
    graph isn't trivial anymore.
    """

    def build_chain(self, classes):
        nodes = [cls() for cls in classes]
        for i in range(len(nodes)):
            nodes[i].chain(nodes[i-1])
        return nodes

    def check_non_resurrecting_chain(self, classes):
        N = len(classes)
        with SimpleBase.test():
            nodes = self.build_chain(classes)
            ids = [id(s) for s in nodes]
            wrs = [weakref.ref(s) for s in nodes]
            del nodes
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])
            self.assertEqual([wr() for wr in wrs], [None] * N)
            gc.collect()
            self.assert_del_calls(ids)

    def check_resurrecting_chain(self, classes):
        N = len(classes)
        with SimpleBase.test():
            nodes = self.build_chain(classes)
            N = len(nodes)
            ids = [id(s) for s in nodes]
            survivor_ids = [id(s) for s in nodes if isinstance(s, SimpleResurrector)]
            wrs = [weakref.ref(s) for s in nodes]
            del nodes
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors(survivor_ids)
            # XXX desirable?
            self.assertEqual([wr() for wr in wrs], [None] * N)
            self.clear_survivors()
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_survivors([])

    def test_homogenous(self):
        self.check_non_resurrecting_chain([SimpleChained] * 3)

    def test_homogenous_resurrect(self):
        self.check_resurrecting_chain([ChainedResurrector] * 3)

    def test_homogenous_suicidal(self):
        self.check_non_resurrecting_chain([SuicidalChained] * 3)

    def test_heterogenous_suicidal_one(self):
        self.check_non_resurrecting_chain([SuicidalChained, SimpleChained] * 2)

    def test_heterogenous_suicidal_two(self):
        self.check_non_resurrecting_chain(
            [SuicidalChained] * 2 + [SimpleChained] * 2)

    def test_heterogenous_resurrect_one(self):
        self.check_resurrecting_chain([ChainedResurrector, SimpleChained] * 2)

    def test_heterogenous_resurrect_two(self):
        self.check_resurrecting_chain(
            [ChainedResurrector, SimpleChained, SuicidalChained] * 2)

    def test_heterogenous_resurrect_three(self):
        self.check_resurrecting_chain(
            [ChainedResurrector] * 2 + [SimpleChained] * 2 + [SuicidalChained] * 2)


# NOTE: the tp_del slot isn't automatically inherited, so we have to call
# with_tp_del() for each instantiated class.

class LegacyBase(SimpleBase):

    def __del__(self):
        try:
            # Do not invoke side_effect here, since we are now exercising
            # the tp_del slot.
            if not self._cleaning:
                self.del_calls.append(id(self))
                self.check_sanity()
        except Exception as e:
            self.errors.append(e)

    def __tp_del__(self):
        """
        Legacy (pre-PEP 442) finalizer, mapped to a tp_del slot.
        """
        try:
            if not self._cleaning:
                self.tp_del_calls.append(id(self))
                self.check_sanity()
                self.side_effect()
        except Exception as e:
            self.errors.append(e)

@_testcapi.with_tp_del
class Legacy(LegacyBase):
    pass

@_testcapi.with_tp_del
class LegacyResurrector(LegacyBase):

    def side_effect(self):
        """
        Resurrect self by storing self in a class-wide list.
        """
        self.survivors.append(self)

@_testcapi.with_tp_del
class LegacySelfCycle(SelfCycleBase, LegacyBase):
    pass


class LegacyFinalizationTest(TestBase, unittest.TestCase):
    """
    Test finalization of objects with a tp_del.
    """

    def tearDown(self):
        # These tests need to clean up a bit more, since they create
        # uncollectable objects.
        gc.garbage.clear()
        gc.collect()
        super().tearDown()

    def test_legacy(self):
        with SimpleBase.test():
            s = Legacy()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_tp_del_calls(ids)
            self.assert_survivors([])
            self.assertIs(wr(), None)
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_tp_del_calls(ids)

    def test_legacy_resurrect(self):
        with SimpleBase.test():
            s = LegacyResurrector()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_tp_del_calls(ids)
            self.assert_survivors(ids)
            # weakrefs are cleared before tp_del is called.
            self.assertIs(wr(), None)
            self.clear_survivors()
            gc.collect()
            self.assert_del_calls(ids)
            self.assert_tp_del_calls(ids * 2)
            self.assert_survivors(ids)
        self.assertIs(wr(), None)

    def test_legacy_self_cycle(self):
        # Self-cycles with legacy finalizers end up in gc.garbage.
        with SimpleBase.test():
            s = LegacySelfCycle()
            ids = [id(s)]
            wr = weakref.ref(s)
            del s
            gc.collect()
            self.assert_del_calls([])
            self.assert_tp_del_calls([])
            self.assert_survivors([])
            self.assert_garbage(ids)
            self.assertIsNot(wr(), None)
            # Break the cycle to allow collection
            gc.garbage[0].ref = None
        self.assert_garbage([])
        self.assertIs(wr(), None)


def test_main():
    support.run_unittest(__name__)

if __name__ == "__main__":
    test_main()