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.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()