/Lib/test/test_gc.py
http://unladen-swallow.googlecode.com/ · Python · 617 lines · 390 code · 85 blank · 142 comment · 31 complexity · 3b4cc69c294c0f93c1628f7c88e4e953 MD5 · raw file
- import unittest
- from test.test_support import verbose, run_unittest
- import sys
- import gc
- import weakref
- try:
- import _llvm
- except ImportError:
- _llvm = None
- ### 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
- # If we don't clear the feedback array, the FDO system will hold
- # references to B and C, which prevent gc.collect() from collecting
- # them.
- if _llvm:
- _llvm.clear_feedback(self.test_newinstance)
- 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.assertEqual
- 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_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()