| import unittest |
| from test.support import (verbose, refcount_test, run_unittest, |
| strip_python_stderr) |
| import sys |
| import time |
| import gc |
| import weakref |
| |
| try: |
| import threading |
| except ImportError: |
| threading = 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) |
| |
| 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 __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) |
| |
| 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", 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 = False |
| threads = [] |
| for i in range(N_THREADS): |
| t = threading.Thread(target=run_thread) |
| threads.append(t) |
| for t in threads: |
| t.start() |
| time.sleep(1.0) |
| exit = True |
| for t in threads: |
| t.join() |
| 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 |
| self.assertTrue(gc.is_tracked(gc)) |
| self.assertTrue(gc.is_tracked(UserClass)) |
| self.assertTrue(gc.is_tracked(UserClass())) |
| 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) |
| |
| def test_garbage_at_shutdown(self): |
| import subprocess |
| code = """if 1: |
| import gc |
| class X: |
| def __init__(self, name): |
| self.name = name |
| def __repr__(self): |
| return "<X %%r>" %% self.name |
| def __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) |
| |
| 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) |
| |
| 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() |