Staging
v0.5.1
v0.5.1
https://github.com/python/cpython
Tip revision: c0a9afe2ac1820409e6173bd1893ebee2cf50270 authored by Ned Deily on 15 August 2020, 06:43:26 UTC
3.6.12
3.6.12
Tip revision: c0a9afe
test_gc.py
import unittest
from test.support import (verbose, refcount_test, run_unittest,
strip_python_stderr, cpython_only, start_threads,
temp_dir, requires_type_collecting, TESTFN, unlink)
from test.support.script_helper import assert_python_ok, make_script
import sys
import time
import gc
import weakref
try:
import threading
except ImportError:
threading = None
try:
from _testcapi import with_tp_del
except ImportError:
def with_tp_del(cls):
class C(object):
def __new__(cls, *args, **kwargs):
raise TypeError('requires _testcapi.with_tp_del')
return C
### 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)
@with_tp_del
class Uncollectable(object):
"""Create a reference cycle with multiple __del__ methods.
An object in a reference cycle will never have zero references,
and so must be garbage collected. If one or more objects in the
cycle have __del__ methods, the gc refuses to guess an order,
and leaves the cycle uncollected."""
def __init__(self, partner=None):
if partner is None:
self.partner = Uncollectable(partner=self)
else:
self.partner = partner
def __tp_del__(self):
pass
### 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)
@requires_type_collecting
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)
@cpython_only
def test_legacy_finalizer(self):
# A() is uncollectable if it is part of a cycle, make sure it shows up
# in gc.garbage.
@with_tp_del
class A:
def __tp_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)
@cpython_only
def test_legacy_finalizer_newclass(self):
# A() is uncollectable if it is part of a cycle, make sure it shows up
# in gc.garbage.
@with_tp_del
class A(object):
def __tp_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", d)
gc.collect()
del d
self.assertEqual(gc.collect(), 2)
@refcount_test
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.
# To minimize variations, though, we first store the get_count() results
# and check them at the end.
@refcount_test
def test_get_count(self):
gc.collect()
a, b, c = gc.get_count()
x = []
d, e, f = gc.get_count()
self.assertEqual((b, c), (0, 0))
self.assertEqual((e, f), (0, 0))
# This is less fragile than asserting that a equals 0.
self.assertLess(a, 5)
# Between the two calls to get_count(), at least one object was
# created (the list).
self.assertGreater(d, a)
@refcount_test
def test_collect_generations(self):
gc.collect()
# This object will "trickle" into generation N + 1 after
# each call to collect(N)
x = []
gc.collect(0)
# x is now in gen 1
a, b, c = gc.get_count()
gc.collect(1)
# x is now in gen 2
d, e, f = gc.get_count()
gc.collect(2)
# x is now in gen 3
g, h, i = gc.get_count()
# We don't check a, d, g since their exact values depends on
# internal implementation details of the interpreter.
self.assertEqual((b, c), (1, 0))
self.assertEqual((e, f), (0, 1))
self.assertEqual((h, i), (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()
@unittest.skipUnless(threading, "test meaningless on builds without threads")
def test_trashcan_threads(self):
# Issue #13992: trashcan mechanism should be thread-safe
NESTING = 60
N_THREADS = 2
def sleeper_gen():
"""A generator that releases the GIL when closed or dealloc'ed."""
try:
yield
finally:
time.sleep(0.000001)
class C(list):
# Appending to a list is atomic, which avoids the use of a lock.
inits = []
dels = []
def __init__(self, alist):
self[:] = alist
C.inits.append(None)
def __del__(self):
# This __del__ is called by subtype_dealloc().
C.dels.append(None)
# `g` will release the GIL when garbage-collected. This
# helps assert subtype_dealloc's behaviour when threads
# switch in the middle of it.
g = sleeper_gen()
next(g)
# Now that __del__ is finished, subtype_dealloc will proceed
# to call list_dealloc, which also uses the trashcan mechanism.
def make_nested():
"""Create a sufficiently nested container object so that the
trashcan mechanism is invoked when deallocating it."""
x = C([])
for i in range(NESTING):
x = [C([x])]
del x
def run_thread():
"""Exercise make_nested() in a loop."""
while not exit:
make_nested()
old_switchinterval = sys.getswitchinterval()
sys.setswitchinterval(1e-5)
try:
exit = []
threads = []
for i in range(N_THREADS):
t = threading.Thread(target=run_thread)
threads.append(t)
with start_threads(threads, lambda: exit.append(1)):
time.sleep(1.0)
finally:
sys.setswitchinterval(old_switchinterval)
gc.collect()
self.assertEqual(len(C.inits), len(C.dels))
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] + list(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(b"a"))
self.assertFalse(gc.is_tracked("a"))
self.assertFalse(gc.is_tracked(bytearray(b"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 UserClass:
pass
class UserInt(int):
pass
# Base class is object; no extra fields.
class UserClassSlots:
__slots__ = ()
# Base class is fixed size larger than object; no extra fields.
class UserFloatSlots(float):
__slots__ = ()
# Base class is variable size; no extra fields.
class UserIntSlots(int):
__slots__ = ()
self.assertTrue(gc.is_tracked(gc))
self.assertTrue(gc.is_tracked(UserClass))
self.assertTrue(gc.is_tracked(UserClass()))
self.assertTrue(gc.is_tracked(UserInt()))
self.assertTrue(gc.is_tracked([]))
self.assertTrue(gc.is_tracked(set()))
self.assertFalse(gc.is_tracked(UserClassSlots()))
self.assertFalse(gc.is_tracked(UserFloatSlots()))
self.assertFalse(gc.is_tracked(UserIntSlots()))
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)
def test_bug21435(self):
# This is a poor test - its only virtue is that it happened to
# segfault on Tim's Windows box before the patch for 21435 was
# applied. That's a nasty bug relying on specific pieces of cyclic
# trash appearing in exactly the right order in finalize_garbage()'s
# input list.
# But there's no reliable way to force that order from Python code,
# so over time chances are good this test won't really be testing much
# of anything anymore. Still, if it blows up, there's _some_
# problem ;-)
gc.collect()
class A:
pass
class B:
def __init__(self, x):
self.x = x
def __del__(self):
self.attr = None
def do_work():
a = A()
b = B(A())
a.attr = b
b.attr = a
do_work()
gc.collect() # this blows up (bad C pointer) when it fails
@cpython_only
def test_garbage_at_shutdown(self):
import subprocess
code = """if 1:
import gc
import _testcapi
@_testcapi.with_tp_del
class X:
def __init__(self, name):
self.name = name
def __repr__(self):
return "<X %%r>" %% self.name
def __tp_del__(self):
pass
x = X('first')
x.x = x
x.y = X('second')
del x
gc.set_debug(%s)
"""
def run_command(code):
p = subprocess.Popen([sys.executable, "-Wd", "-c", code],
stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
stdout, stderr = p.communicate()
p.stdout.close()
p.stderr.close()
self.assertEqual(p.returncode, 0)
self.assertEqual(stdout.strip(), b"")
return strip_python_stderr(stderr)
stderr = run_command(code % "0")
self.assertIn(b"ResourceWarning: gc: 2 uncollectable objects at "
b"shutdown; use", stderr)
self.assertNotIn(b"<X 'first'>", stderr)
# With DEBUG_UNCOLLECTABLE, the garbage list gets printed
stderr = run_command(code % "gc.DEBUG_UNCOLLECTABLE")
self.assertIn(b"ResourceWarning: gc: 2 uncollectable objects at "
b"shutdown", stderr)
self.assertTrue(
(b"[<X 'first'>, <X 'second'>]" in stderr) or
(b"[<X 'second'>, <X 'first'>]" in stderr), stderr)
# With DEBUG_SAVEALL, no additional message should get printed
# (because gc.garbage also contains normally reclaimable cyclic
# references, and its elements get printed at runtime anyway).
stderr = run_command(code % "gc.DEBUG_SAVEALL")
self.assertNotIn(b"uncollectable objects at shutdown", stderr)
@requires_type_collecting
def test_gc_main_module_at_shutdown(self):
# Create a reference cycle through the __main__ module and check
# it gets collected at interpreter shutdown.
code = """if 1:
class C:
def __del__(self):
print('__del__ called')
l = [C()]
l.append(l)
"""
rc, out, err = assert_python_ok('-c', code)
self.assertEqual(out.strip(), b'__del__ called')
@requires_type_collecting
def test_gc_ordinary_module_at_shutdown(self):
# Same as above, but with a non-__main__ module.
with temp_dir() as script_dir:
module = """if 1:
class C:
def __del__(self):
print('__del__ called')
l = [C()]
l.append(l)
"""
code = """if 1:
import sys
sys.path.insert(0, %r)
import gctest
""" % (script_dir,)
make_script(script_dir, 'gctest', module)
rc, out, err = assert_python_ok('-c', code)
self.assertEqual(out.strip(), b'__del__ called')
@requires_type_collecting
def test_global_del_SystemExit(self):
code = """if 1:
class ClassWithDel:
def __del__(self):
print('__del__ called')
a = ClassWithDel()
a.link = a
raise SystemExit(0)"""
self.addCleanup(unlink, TESTFN)
with open(TESTFN, 'w') as script:
script.write(code)
rc, out, err = assert_python_ok(TESTFN)
self.assertEqual(out.strip(), b'__del__ called')
def test_get_stats(self):
stats = gc.get_stats()
self.assertEqual(len(stats), 3)
for st in stats:
self.assertIsInstance(st, dict)
self.assertEqual(set(st),
{"collected", "collections", "uncollectable"})
self.assertGreaterEqual(st["collected"], 0)
self.assertGreaterEqual(st["collections"], 0)
self.assertGreaterEqual(st["uncollectable"], 0)
# Check that collection counts are incremented correctly
if gc.isenabled():
self.addCleanup(gc.enable)
gc.disable()
old = gc.get_stats()
gc.collect(0)
new = gc.get_stats()
self.assertEqual(new[0]["collections"], old[0]["collections"] + 1)
self.assertEqual(new[1]["collections"], old[1]["collections"])
self.assertEqual(new[2]["collections"], old[2]["collections"])
gc.collect(2)
new = gc.get_stats()
self.assertEqual(new[0]["collections"], old[0]["collections"] + 1)
self.assertEqual(new[1]["collections"], old[1]["collections"])
self.assertEqual(new[2]["collections"], old[2]["collections"] + 1)
class GCCallbackTests(unittest.TestCase):
def setUp(self):
# Save gc state and disable it.
self.enabled = gc.isenabled()
gc.disable()
self.debug = gc.get_debug()
gc.set_debug(0)
gc.callbacks.append(self.cb1)
gc.callbacks.append(self.cb2)
self.othergarbage = []
def tearDown(self):
# Restore gc state
del self.visit
gc.callbacks.remove(self.cb1)
gc.callbacks.remove(self.cb2)
gc.set_debug(self.debug)
if self.enabled:
gc.enable()
# destroy any uncollectables
gc.collect()
for obj in gc.garbage:
if isinstance(obj, Uncollectable):
obj.partner = None
del gc.garbage[:]
del self.othergarbage
gc.collect()
def preclean(self):
# Remove all fluff from the system. Invoke this function
# manually rather than through self.setUp() for maximum
# safety.
self.visit = []
gc.collect()
garbage, gc.garbage[:] = gc.garbage[:], []
self.othergarbage.append(garbage)
self.visit = []
def cb1(self, phase, info):
self.visit.append((1, phase, dict(info)))
def cb2(self, phase, info):
self.visit.append((2, phase, dict(info)))
if phase == "stop" and hasattr(self, "cleanup"):
# Clean Uncollectable from garbage
uc = [e for e in gc.garbage if isinstance(e, Uncollectable)]
gc.garbage[:] = [e for e in gc.garbage
if not isinstance(e, Uncollectable)]
for e in uc:
e.partner = None
def test_collect(self):
self.preclean()
gc.collect()
# Algorithmically verify the contents of self.visit
# because it is long and tortuous.
# Count the number of visits to each callback
n = [v[0] for v in self.visit]
n1 = [i for i in n if i == 1]
n2 = [i for i in n if i == 2]
self.assertEqual(n1, [1]*2)
self.assertEqual(n2, [2]*2)
# Count that we got the right number of start and stop callbacks.
n = [v[1] for v in self.visit]
n1 = [i for i in n if i == "start"]
n2 = [i for i in n if i == "stop"]
self.assertEqual(n1, ["start"]*2)
self.assertEqual(n2, ["stop"]*2)
# Check that we got the right info dict for all callbacks
for v in self.visit:
info = v[2]
self.assertTrue("generation" in info)
self.assertTrue("collected" in info)
self.assertTrue("uncollectable" in info)
def test_collect_generation(self):
self.preclean()
gc.collect(2)
for v in self.visit:
info = v[2]
self.assertEqual(info["generation"], 2)
@cpython_only
def test_collect_garbage(self):
self.preclean()
# Each of these cause four objects to be garbage: Two
# Uncolectables and their instance dicts.
Uncollectable()
Uncollectable()
C1055820(666)
gc.collect()
for v in self.visit:
if v[1] != "stop":
continue
info = v[2]
self.assertEqual(info["collected"], 2)
self.assertEqual(info["uncollectable"], 8)
# We should now have the Uncollectables in gc.garbage
self.assertEqual(len(gc.garbage), 4)
for e in gc.garbage:
self.assertIsInstance(e, Uncollectable)
# Now, let our callback handle the Uncollectable instances
self.cleanup=True
self.visit = []
gc.garbage[:] = []
gc.collect()
for v in self.visit:
if v[1] != "stop":
continue
info = v[2]
self.assertEqual(info["collected"], 0)
self.assertEqual(info["uncollectable"], 4)
# Uncollectables should be gone
self.assertEqual(len(gc.garbage), 0)
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, GCCallbackTests)
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()
