summaryrefslogtreecommitdiffstats
path: root/Lib/test/test_gc.py
blob: 5a35dec8c18c49c7556b830a058bdd5874f55344 (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
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
import unittest
from test.test_support import verbose, run_unittest
import sys
import gc
import weakref

### Support code
###############################################################################

# Bug 1055820 has several tests of longstanding bugs involving weakrefs and
# cyclic gc.

# An instance of C1055820 has a self-loop, so becomes cyclic trash when
# unreachable.
class C1055820(object):
    def __init__(self, i):
        self.i = i
        self.loop = self

class GC_Detector(object):
    # Create an instance I.  Then gc hasn't happened again so long as
    # I.gc_happened is false.

    def __init__(self):
        self.gc_happened = False

        def it_happened(ignored):
            self.gc_happened = True

        # Create a piece of cyclic trash that triggers it_happened when
        # gc collects it.
        self.wr = weakref.ref(C1055820(666), it_happened)


### Tests
###############################################################################

class GCTests(unittest.TestCase):
    def test_list(self):
        l = []
        l.append(l)
        gc.collect()
        del l
        self.assertEqual(gc.collect(), 1)

    def test_dict(self):
        d = {}
        d[1] = d
        gc.collect()
        del d
        self.assertEqual(gc.collect(), 1)

    def test_tuple(self):
        # since tuples are immutable we close the loop with a list
        l = []
        t = (l,)
        l.append(t)
        gc.collect()
        del t
        del l
        self.assertEqual(gc.collect(), 2)

    def test_class(self):
        class A:
            pass
        A.a = A
        gc.collect()
        del A
        self.assertNotEqual(gc.collect(), 0)

    def test_newstyleclass(self):
        class A(object):
            pass
        gc.collect()
        del A
        self.assertNotEqual(gc.collect(), 0)

    def test_instance(self):
        class A:
            pass
        a = A()
        a.a = a
        gc.collect()
        del a
        self.assertNotEqual(gc.collect(), 0)

    def test_newinstance(self):
        class A(object):
            pass
        a = A()
        a.a = a
        gc.collect()
        del a
        self.assertNotEqual(gc.collect(), 0)
        class B(list):
            pass
        class C(B, A):
            pass
        a = C()
        a.a = a
        gc.collect()
        del a
        self.assertNotEqual(gc.collect(), 0)
        del B, C
        self.assertNotEqual(gc.collect(), 0)
        A.a = A()
        del A
        self.assertNotEqual(gc.collect(), 0)
        self.assertEqual(gc.collect(), 0)

    def test_method(self):
        # Tricky: self.__init__ is a bound method, it references the instance.
        class A:
            def __init__(self):
                self.init = self.__init__
        a = A()
        gc.collect()
        del a
        self.assertNotEqual(gc.collect(), 0)

    def test_finalizer(self):
        # A() is uncollectable if it is part of a cycle, make sure it shows up
        # in gc.garbage.
        class A:
            def __del__(self): pass
        class B:
            pass
        a = A()
        a.a = a
        id_a = id(a)
        b = B()
        b.b = b
        gc.collect()
        del a
        del b
        self.assertNotEqual(gc.collect(), 0)
        for obj in gc.garbage:
            if id(obj) == id_a:
                del obj.a
                break
        else:
            self.fail("didn't find obj in garbage (finalizer)")
        gc.garbage.remove(obj)

    def test_finalizer_newclass(self):
        # A() is uncollectable if it is part of a cycle, make sure it shows up
        # in gc.garbage.
        class A(object):
            def __del__(self): pass
        class B(object):
            pass
        a = A()
        a.a = a
        id_a = id(a)
        b = B()
        b.b = b
        gc.collect()
        del a
        del b
        self.assertNotEqual(gc.collect(), 0)
        for obj in gc.garbage:
            if id(obj) == id_a:
                del obj.a
                break
        else:
            self.fail("didn't find obj in garbage (finalizer)")
        gc.garbage.remove(obj)

    def test_function(self):
        # Tricky: f -> d -> f, code should call d.clear() after the exec to
        # break the cycle.
        d = {}
        exec("def f(): pass\n") in d
        gc.collect()
        del d
        self.assertEqual(gc.collect(), 2)

    def test_frame(self):
        def f():
            frame = sys._getframe()
        gc.collect()
        f()
        self.assertEqual(gc.collect(), 1)

    def test_saveall(self):
        # Verify that cyclic garbage like lists show up in gc.garbage if the
        # SAVEALL option is enabled.

        # First make sure we don't save away other stuff that just happens to
        # be waiting for collection.
        gc.collect()
        # if this fails, someone else created immortal trash
        self.assertEqual(gc.garbage, [])

        L = []
        L.append(L)
        id_L = id(L)

        debug = gc.get_debug()
        gc.set_debug(debug | gc.DEBUG_SAVEALL)
        del L
        gc.collect()
        gc.set_debug(debug)

        self.assertEqual(len(gc.garbage), 1)
        obj = gc.garbage.pop()
        self.assertEqual(id(obj), id_L)

    def test_del(self):
        # __del__ methods can trigger collection, make this to happen
        thresholds = gc.get_threshold()
        gc.enable()
        gc.set_threshold(1)

        class A:
            def __del__(self):
                dir(self)
        a = A()
        del a

        gc.disable()
        gc.set_threshold(*thresholds)

    def test_del_newclass(self):
        # __del__ methods can trigger collection, make this to happen
        thresholds = gc.get_threshold()
        gc.enable()
        gc.set_threshold(1)

        class A(object):
            def __del__(self):
                dir(self)
        a = A()
        del a

        gc.disable()
        gc.set_threshold(*thresholds)

    # The following two tests are fragile:
    # They precisely count the number of allocations,
    # which is highly implementation-dependent.
    # For example:
    # - disposed tuples are not freed, but reused
    # - the call to assertEqual somehow avoids building its args tuple
    def test_get_count(self):
        # Avoid future allocation of method object
        assertEqual = self._baseAssertEqual
        gc.collect()
        assertEqual(gc.get_count(), (0, 0, 0))
        a = dict()
        # since gc.collect(), we created two objects:
        # the dict, and the tuple returned by get_count()
        assertEqual(gc.get_count(), (2, 0, 0))

    def test_collect_generations(self):
        # Avoid future allocation of method object
        assertEqual = self.assertEqual
        gc.collect()
        a = dict()
        gc.collect(0)
        assertEqual(gc.get_count(), (0, 1, 0))
        gc.collect(1)
        assertEqual(gc.get_count(), (0, 0, 1))
        gc.collect(2)
        assertEqual(gc.get_count(), (0, 0, 0))

    def test_trashcan(self):
        class Ouch:
            n = 0
            def __del__(self):
                Ouch.n = Ouch.n + 1
                if Ouch.n % 17 == 0:
                    gc.collect()

        # "trashcan" is a hack to prevent stack overflow when deallocating
        # very deeply nested tuples etc.  It works in part by abusing the
        # type pointer and refcount fields, and that can yield horrible
        # problems when gc tries to traverse the structures.
        # If this test fails (as it does in 2.0, 2.1 and 2.2), it will
        # most likely die via segfault.

        # Note:  In 2.3 the possibility for compiling without cyclic gc was
        # removed, and that in turn allows the trashcan mechanism to work
        # via much simpler means (e.g., it never abuses the type pointer or
        # refcount fields anymore).  Since it's much less likely to cause a
        # problem now, the various constants in this expensive (we force a lot
        # of full collections) test are cut back from the 2.2 version.
        gc.enable()
        N = 150
        for count in range(2):
            t = []
            for i in range(N):
                t = [t, Ouch()]
            u = []
            for i in range(N):
                u = [u, Ouch()]
            v = {}
            for i in range(N):
                v = {1: v, 2: Ouch()}
        gc.disable()

    def test_boom(self):
        class Boom:
            def __getattr__(self, someattribute):
                del self.attr
                raise AttributeError

        a = Boom()
        b = Boom()
        a.attr = b
        b.attr = a

        gc.collect()
        garbagelen = len(gc.garbage)
        del a, b
        # a<->b are in a trash cycle now.  Collection will invoke
        # Boom.__getattr__ (to see whether a and b have __del__ methods), and
        # __getattr__ deletes the internal "attr" attributes as a side effect.
        # That causes the trash cycle to get reclaimed via refcounts falling to
        # 0, thus mutating the trash graph as a side effect of merely asking
        # whether __del__ exists.  This used to (before 2.3b1) crash Python.
        # Now __getattr__ isn't called.
        self.assertEqual(gc.collect(), 4)
        self.assertEqual(len(gc.garbage), garbagelen)

    def test_boom2(self):
        class Boom2:
            def __init__(self):
                self.x = 0

            def __getattr__(self, someattribute):
                self.x += 1
                if self.x > 1:
                    del self.attr
                raise AttributeError

        a = Boom2()
        b = Boom2()
        a.attr = b
        b.attr = a

        gc.collect()
        garbagelen = len(gc.garbage)
        del a, b
        # Much like test_boom(), except that __getattr__ doesn't break the
        # cycle until the second time gc checks for __del__.  As of 2.3b1,
        # there isn't a second time, so this simply cleans up the trash cycle.
        # We expect a, b, a.__dict__ and b.__dict__ (4 objects) to get
        # reclaimed this way.
        self.assertEqual(gc.collect(), 4)
        self.assertEqual(len(gc.garbage), garbagelen)

    def test_boom_new(self):
        # boom__new and boom2_new are exactly like boom and boom2, except use
        # new-style classes.

        class Boom_New(object):
            def __getattr__(self, someattribute):
                del self.attr
                raise AttributeError

        a = Boom_New()
        b = Boom_New()
        a.attr = b
        b.attr = a

        gc.collect()
        garbagelen = len(gc.garbage)
        del a, b
        self.assertEqual(gc.collect(), 4)
        self.assertEqual(len(gc.garbage), garbagelen)

    def test_boom2_new(self):
        class Boom2_New(object):
            def __init__(self):
                self.x = 0

            def __getattr__(self, someattribute):
                self.x += 1
                if self.x > 1:
                    del self.attr
                raise AttributeError

        a = Boom2_New()
        b = Boom2_New()
        a.attr = b
        b.attr = a

        gc.collect()
        garbagelen = len(gc.garbage)
        del a, b
        self.assertEqual(gc.collect(), 4)
        self.assertEqual(len(gc.garbage), garbagelen)

    def test_get_referents(self):
        alist = [1, 3, 5]
        got = gc.get_referents(alist)
        got.sort()
        self.assertEqual(got, alist)

        atuple = tuple(alist)
        got = gc.get_referents(atuple)
        got.sort()
        self.assertEqual(got, alist)

        adict = {1: 3, 5: 7}
        expected = [1, 3, 5, 7]
        got = gc.get_referents(adict)
        got.sort()
        self.assertEqual(got, expected)

        got = gc.get_referents([1, 2], {3: 4}, (0, 0, 0))
        got.sort()
        self.assertEqual(got, [0, 0] + range(5))

        self.assertEqual(gc.get_referents(1, 'a', 4j), [])

    def test_is_tracked(self):
        # Atomic built-in types are not tracked, user-defined objects and
        # mutable containers are.
        # NOTE: types with special optimizations (e.g. tuple) have tests
        # in their own test files instead.
        self.assertFalse(gc.is_tracked(None))
        self.assertFalse(gc.is_tracked(1))
        self.assertFalse(gc.is_tracked(1.0))
        self.assertFalse(gc.is_tracked(1.0 + 5.0j))
        self.assertFalse(gc.is_tracked(True))
        self.assertFalse(gc.is_tracked(False))
        self.assertFalse(gc.is_tracked("a"))
        self.assertFalse(gc.is_tracked(u"a"))
        self.assertFalse(gc.is_tracked(bytearray("a")))
        self.assertFalse(gc.is_tracked(type))
        self.assertFalse(gc.is_tracked(int))
        self.assertFalse(gc.is_tracked(object))
        self.assertFalse(gc.is_tracked(object()))

        class OldStyle:
            pass
        class NewStyle(object):
            pass
        self.assertTrue(gc.is_tracked(gc))
        self.assertTrue(gc.is_tracked(OldStyle))
        self.assertTrue(gc.is_tracked(OldStyle()))
        self.assertTrue(gc.is_tracked(NewStyle))
        self.assertTrue(gc.is_tracked(NewStyle()))
        self.assertTrue(gc.is_tracked([]))
        self.assertTrue(gc.is_tracked(set()))

    def test_bug1055820b(self):
        # Corresponds to temp2b.py in the bug report.

        ouch = []
        def callback(ignored):
            ouch[:] = [wr() for wr in WRs]

        Cs = [C1055820(i) for i in range(2)]
        WRs = [weakref.ref(c, callback) for c in Cs]
        c = None

        gc.collect()
        self.assertEqual(len(ouch), 0)
        # Make the two instances trash, and collect again.  The bug was that
        # the callback materialized a strong reference to an instance, but gc
        # cleared the instance's dict anyway.
        Cs = None
        gc.collect()
        self.assertEqual(len(ouch), 2)  # else the callbacks didn't run
        for x in ouch:
            # If the callback resurrected one of these guys, the instance
            # would be damaged, with an empty __dict__.
            self.assertEqual(x, None)

class GCTogglingTests(unittest.TestCase):
    def setUp(self):
        gc.enable()

    def tearDown(self):
        gc.disable()

    def test_bug1055820c(self):
        # Corresponds to temp2c.py in the bug report.  This is pretty
        # elaborate.

        c0 = C1055820(0)
        # Move c0 into generation 2.
        gc.collect()

        c1 = C1055820(1)
        c1.keep_c0_alive = c0
        del c0.loop # now only c1 keeps c0 alive

        c2 = C1055820(2)
        c2wr = weakref.ref(c2) # no callback!

        ouch = []
        def callback(ignored):
            ouch[:] = [c2wr()]

        # The callback gets associated with a wr on an object in generation 2.
        c0wr = weakref.ref(c0, callback)

        c0 = c1 = c2 = None

        # What we've set up:  c0, c1, and c2 are all trash now.  c0 is in
        # generation 2.  The only thing keeping it alive is that c1 points to
        # it. c1 and c2 are in generation 0, and are in self-loops.  There's a
        # global weakref to c2 (c2wr), but that weakref has no callback.
        # There's also a global weakref to c0 (c0wr), and that does have a
        # callback, and that callback references c2 via c2wr().
        #
        #               c0 has a wr with callback, which references c2wr
        #               ^
        #               |
        #               |     Generation 2 above dots
        #. . . . . . . .|. . . . . . . . . . . . . . . . . . . . . . . .
        #               |     Generation 0 below dots
        #               |
        #               |
        #            ^->c1   ^->c2 has a wr but no callback
        #            |  |    |  |
        #            <--v    <--v
        #
        # So this is the nightmare:  when generation 0 gets collected, we see
        # that c2 has a callback-free weakref, and c1 doesn't even have a
        # weakref.  Collecting generation 0 doesn't see c0 at all, and c0 is
        # the only object that has a weakref with a callback.  gc clears c1
        # and c2.  Clearing c1 has the side effect of dropping the refcount on
        # c0 to 0, so c0 goes away (despite that it's in an older generation)
        # and c0's wr callback triggers.  That in turn materializes a reference
        # to c2 via c2wr(), but c2 gets cleared anyway by gc.

        # We want to let gc happen "naturally", to preserve the distinction
        # between generations.
        junk = []
        i = 0
        detector = GC_Detector()
        while not detector.gc_happened:
            i += 1
            if i > 10000:
                self.fail("gc didn't happen after 10000 iterations")
            self.assertEqual(len(ouch), 0)
            junk.append([])  # this will eventually trigger gc

        self.assertEqual(len(ouch), 1)  # else the callback wasn't invoked
        for x in ouch:
            # If the callback resurrected c2, the instance would be damaged,
            # with an empty __dict__.
            self.assertEqual(x, None)

    def test_bug1055820d(self):
        # Corresponds to temp2d.py in the bug report.  This is very much like
        # test_bug1055820c, but uses a __del__ method instead of a weakref
        # callback to sneak in a resurrection of cyclic trash.

        ouch = []
        class D(C1055820):
            def __del__(self):
                ouch[:] = [c2wr()]

        d0 = D(0)
        # Move all the above into generation 2.
        gc.collect()

        c1 = C1055820(1)
        c1.keep_d0_alive = d0
        del d0.loop # now only c1 keeps d0 alive

        c2 = C1055820(2)
        c2wr = weakref.ref(c2) # no callback!

        d0 = c1 = c2 = None

        # What we've set up:  d0, c1, and c2 are all trash now.  d0 is in
        # generation 2.  The only thing keeping it alive is that c1 points to
        # it.  c1 and c2 are in generation 0, and are in self-loops.  There's
        # a global weakref to c2 (c2wr), but that weakref has no callback.
        # There are no other weakrefs.
        #
        #               d0 has a __del__ method that references c2wr
        #               ^
        #               |
        #               |     Generation 2 above dots
        #. . . . . . . .|. . . . . . . . . . . . . . . . . . . . . . . .
        #               |     Generation 0 below dots
        #               |
        #               |
        #            ^->c1   ^->c2 has a wr but no callback
        #            |  |    |  |
        #            <--v    <--v
        #
        # So this is the nightmare:  when generation 0 gets collected, we see
        # that c2 has a callback-free weakref, and c1 doesn't even have a
        # weakref.  Collecting generation 0 doesn't see d0 at all.  gc clears
        # c1 and c2.  Clearing c1 has the side effect of dropping the refcount
        # on d0 to 0, so d0 goes away (despite that it's in an older
        # generation) and d0's __del__ triggers.  That in turn materializes
        # a reference to c2 via c2wr(), but c2 gets cleared anyway by gc.

        # We want to let gc happen "naturally", to preserve the distinction
        # between generations.
        detector = GC_Detector()
        junk = []
        i = 0
        while not detector.gc_happened:
            i += 1
            if i > 10000:
                self.fail("gc didn't happen after 10000 iterations")
            self.assertEqual(len(ouch), 0)
            junk.append([])  # this will eventually trigger gc

        self.assertEqual(len(ouch), 1)  # else __del__ wasn't invoked
        for x in ouch:
            # If __del__ resurrected c2, the instance would be damaged, with an
            # empty __dict__.
            self.assertEqual(x, None)

def test_main():
    enabled = gc.isenabled()
    gc.disable()
    assert not gc.isenabled()
    debug = gc.get_debug()
    gc.set_debug(debug & ~gc.DEBUG_LEAK) # this test is supposed to leak

    try:
        gc.collect() # Delete 2nd generation garbage
        run_unittest(GCTests, GCTogglingTests)
    finally:
        gc.set_debug(debug)
        # test gc.enable() even if GC is disabled by default
        if verbose:
            print "restoring automatic collection"
        # make sure to always test gc.enable()
        gc.enable()
        assert gc.isenabled()
        if not enabled:
            gc.disable()

if __name__ == "__main__":
    test_main()