Lib/test/test_gc.py

   1 from test.test_support import verify, verbose, TestFailed, vereq
   2 import sys
   3 import gc
   4
   5 def expect(actual, expected, name):
   6     if actual != expected:
   7         raise TestFailed, "test_%s: actual %r, expected %r" % (
   8             name, actual, expected)
   9
  10 def expect_nonzero(actual, name):
  11     if actual == 0:
  12         raise TestFailed, "test_%s: unexpected zero" % name
  13
  14 def run_test(name, thunk):
  15     if verbose:
  16         print "testing %s..." % name,
  17     thunk()
  18     if verbose:
  19         print "ok"
  20
  21 def test_list():
  22     l = []
  23     l.append(l)
  24     gc.collect()
  25     del l
  26     expect(gc.collect(), 1, "list")
  27
  28 def test_dict():
  29     d = {}
  30     d[1] = d
  31     gc.collect()
  32     del d
  33     expect(gc.collect(), 1, "dict")
  34
  35 def test_tuple():
  36     # since tuples are immutable we close the loop with a list
  37     l = []
  38     t = (l,)
  39     l.append(t)
  40     gc.collect()
  41     del t
  42     del l
  43     expect(gc.collect(), 2, "tuple")
  44
  45 def test_class():
  46     class A:
  47         pass
  48     A.a = A
  49     gc.collect()
  50     del A
  51     expect_nonzero(gc.collect(), "class")
  52
  53 def test_newstyleclass():
  54     class A(object):
  55         pass
  56     gc.collect()
  57     del A
  58     expect_nonzero(gc.collect(), "staticclass")
  59
  60 def test_instance():
  61     class A:
  62         pass
  63     a = A()
  64     a.a = a
  65     gc.collect()
  66     del a
  67     expect_nonzero(gc.collect(), "instance")
  68
  69 def test_newinstance():
  70     class A(object):
  71         pass
  72     a = A()
  73     a.a = a
  74     gc.collect()
  75     del a
  76     expect_nonzero(gc.collect(), "newinstance")
  77     class B(list):
  78         pass
  79     class C(B, A):
  80         pass
  81     a = C()
  82     a.a = a
  83     gc.collect()
  84     del a
  85     expect_nonzero(gc.collect(), "newinstance(2)")
  86     del B, C
  87     expect_nonzero(gc.collect(), "newinstance(3)")
  88     A.a = A()
  89     del A
  90     expect_nonzero(gc.collect(), "newinstance(4)")
  91     expect(gc.collect(), 0, "newinstance(5)")
  92
  93 def test_method():
  94     # Tricky: self.__init__ is a bound method, it references the instance.
  95     class A:
  96         def __init__(self):
  97             self.init = self.__init__
  98     a = A()
  99     gc.collect()
 100     del a
 101     expect_nonzero(gc.collect(), "method")
 102
 103 def test_finalizer():
 104     # A() is uncollectable if it is part of a cycle, make sure it shows up
 105     # in gc.garbage.
 106     class A:
 107         def __del__(self): pass
 108     class B:
 109         pass
 110     a = A()
 111     a.a = a
 112     id_a = id(a)
 113     b = B()
 114     b.b = b
 115     gc.collect()
 116     del a
 117     del b
 118     expect_nonzero(gc.collect(), "finalizer")
 119     for obj in gc.garbage:
 120         if id(obj) == id_a:
 121             del obj.a
 122             break
 123     else:
 124         raise TestFailed, "didn't find obj in garbage (finalizer)"
 125     gc.garbage.remove(obj)
 126
 127 def test_finalizer_newclass():
 128     # A() is uncollectable if it is part of a cycle, make sure it shows up
 129     # in gc.garbage.
 130     class A(object):
 131         def __del__(self): pass
 132     class B(object):
 133         pass
 134     a = A()
 135     a.a = a
 136     id_a = id(a)
 137     b = B()
 138     b.b = b
 139     gc.collect()
 140     del a
 141     del b
 142     expect_nonzero(gc.collect(), "finalizer")
 143     for obj in gc.garbage:
 144         if id(obj) == id_a:
 145             del obj.a
 146             break
 147     else:
 148         raise TestFailed, "didn't find obj in garbage (finalizer)"
 149     gc.garbage.remove(obj)
 150
 151 def test_function():
 152     # Tricky: f -> d -> f, code should call d.clear() after the exec to
 153     # break the cycle.
 154     d = {}
 155     exec("def f(): pass\n") in d
 156     gc.collect()
 157     del d
 158     expect(gc.collect(), 2, "function")
 159
 160 def test_frame():
 161     def f():
 162         frame = sys._getframe()
 163     gc.collect()
 164     f()
 165     expect(gc.collect(), 1, "frame")
 166
 167
 168 def test_saveall():
 169     # Verify that cyclic garbage like lists show up in gc.garbage if the
 170     # SAVEALL option is enabled.
 171
 172     # First make sure we don't save away other stuff that just happens to
 173     # be waiting for collection.
 174     gc.collect()
 175     vereq(gc.garbage, []) # if this fails, someone else created immortal trash
 176
 177     L = []
 178     L.append(L)
 179     id_L = id(L)
 180
 181     debug = gc.get_debug()
 182     gc.set_debug(debug | gc.DEBUG_SAVEALL)
 183     del L
 184     gc.collect()
 185     gc.set_debug(debug)
 186
 187     vereq(len(gc.garbage), 1)
 188     obj = gc.garbage.pop()
 189     vereq(id(obj), id_L)
 190
 191 def test_del():
 192     # __del__ methods can trigger collection, make this to happen
 193     thresholds = gc.get_threshold()
 194     gc.enable()
 195     gc.set_threshold(1)
 196
 197     class A:
 198         def __del__(self):
 199             dir(self)
 200     a = A()
 201     del a
 202
 203     gc.disable()
 204     gc.set_threshold(*thresholds)
 205
 206 def test_del_newclass():
 207     # __del__ methods can trigger collection, make this to happen
 208     thresholds = gc.get_threshold()
 209     gc.enable()
 210     gc.set_threshold(1)
 211
 212     class A(object):
 213         def __del__(self):
 214             dir(self)
 215     a = A()
 216     del a
 217
 218     gc.disable()
 219     gc.set_threshold(*thresholds)
 220
 221 class Ouch:
 222     n = 0
 223     def __del__(self):
 224         Ouch.n = Ouch.n + 1
 225         if Ouch.n % 17 == 0:
 226             gc.collect()
 227
 228 def test_trashcan():
 229     # "trashcan" is a hack to prevent stack overflow when deallocating
 230     # very deeply nested tuples etc.  It works in part by abusing the
 231     # type pointer and refcount fields, and that can yield horrible
 232     # problems when gc tries to traverse the structures.
 233     # If this test fails (as it does in 2.0, 2.1 and 2.2), it will
 234     # most likely die via segfault.
 235
 236     # Note:  In 2.3 the possibility for compiling without cyclic gc was
 237     # removed, and that in turn allows the trashcan mechanism to work
 238     # via much simpler means (e.g., it never abuses the type pointer or
 239     # refcount fields anymore).  Since it's much less likely to cause a
 240     # problem now, the various constants in this expensive (we force a lot
 241     # of full collections) test are cut back from the 2.2 version.
 242     gc.enable()
 243     N = 150
 244     for count in range(2):
 245         t = []
 246         for i in range(N):
 247             t = [t, Ouch()]
 248         u = []
 249         for i in range(N):
 250             u = [u, Ouch()]
 251         v = {}
 252         for i in range(N):
 253             v = {1: v, 2: Ouch()}
 254     gc.disable()
 255
 256 class Boom:
 257     def __getattr__(self, someattribute):
 258         del self.attr
 259         raise AttributeError
 260
 261 def test_boom():
 262     a = Boom()
 263     b = Boom()
 264     a.attr = b
 265     b.attr = a
 266
 267     gc.collect()
 268     garbagelen = len(gc.garbage)
 269     del a, b
 270     # a<->b are in a trash cycle now.  Collection will invoke Boom.__getattr__
 271     # (to see whether a and b have __del__ methods), and __getattr__ deletes
 272     # the internal "attr" attributes as a side effect.  That causes the
 273     # trash cycle to get reclaimed via refcounts falling to 0, thus mutating
 274     # the trash graph as a side effect of merely asking whether __del__
 275     # exists.  This used to (before 2.3b1) crash Python.  Now __getattr__
 276     # isn't called.
 277     expect(gc.collect(), 4, "boom")
 278     expect(len(gc.garbage), garbagelen, "boom")
 279
 280 class Boom2:
 281     def __init__(self):
 282         self.x = 0
 283
 284     def __getattr__(self, someattribute):
 285         self.x += 1
 286         if self.x > 1:
 287             del self.attr
 288         raise AttributeError
 289
 290 def test_boom2():
 291     a = Boom2()
 292     b = Boom2()
 293     a.attr = b
 294     b.attr = a
 295
 296     gc.collect()
 297     garbagelen = len(gc.garbage)
 298     del a, b
 299     # Much like test_boom(), except that __getattr__ doesn't break the
 300     # cycle until the second time gc checks for __del__.  As of 2.3b1,
 301     # there isn't a second time, so this simply cleans up the trash cycle.
 302     # We expect a, b, a.__dict__ and b.__dict__ (4 objects) to get reclaimed
 303     # this way.
 304     expect(gc.collect(), 4, "boom2")
 305     expect(len(gc.garbage), garbagelen, "boom2")
 306
 307 # boom__new and boom2_new are exactly like boom and boom2, except use
 308 # new-style classes.
 309
 310 class Boom_New(object):
 311     def __getattr__(self, someattribute):
 312         del self.attr
 313         raise AttributeError
 314
 315 def test_boom_new():
 316     a = Boom_New()
 317     b = Boom_New()
 318     a.attr = b
 319     b.attr = a
 320
 321     gc.collect()
 322     garbagelen = len(gc.garbage)
 323     del a, b
 324     expect(gc.collect(), 4, "boom_new")
 325     expect(len(gc.garbage), garbagelen, "boom_new")
 326
 327 class Boom2_New(object):
 328     def __init__(self):
 329         self.x = 0
 330
 331     def __getattr__(self, someattribute):
 332         self.x += 1
 333         if self.x > 1:
 334             del self.attr
 335         raise AttributeError
 336
 337 def test_boom2_new():
 338     a = Boom2_New()
 339     b = Boom2_New()
 340     a.attr = b
 341     b.attr = a
 342
 343     gc.collect()
 344     garbagelen = len(gc.garbage)
 345     del a, b
 346     expect(gc.collect(), 4, "boom2_new")
 347     expect(len(gc.garbage), garbagelen, "boom2_new")
 348
 349 def test_get_referents():
 350     alist = [1, 3, 5]
 351     got = gc.get_referents(alist)
 352     got.sort()
 353     expect(got, alist, "get_referents")
 354
 355     atuple = tuple(alist)
 356     got = gc.get_referents(atuple)
 357     got.sort()
 358     expect(got, alist, "get_referents")
 359
 360     adict = {1: 3, 5: 7}
 361     expected = [1, 3, 5, 7]
 362     got = gc.get_referents(adict)
 363     got.sort()
 364     expect(got, expected, "get_referents")
 365
 366     got = gc.get_referents([1, 2], {3: 4}, (0, 0, 0))
 367     got.sort()
 368     expect(got, [0, 0] + range(5), "get_referents")
 369
 370     expect(gc.get_referents(1, 'a', 4j), [], "get_referents")
 371
 372 def test_all():
 373     gc.collect() # Delete 2nd generation garbage
 374     run_test("lists", test_list)
 375     run_test("dicts", test_dict)
 376     run_test("tuples", test_tuple)
 377     run_test("classes", test_class)
 378     run_test("new style classes", test_newstyleclass)
 379     run_test("instances", test_instance)
 380     run_test("new instances", test_newinstance)
 381     run_test("methods", test_method)
 382     run_test("functions", test_function)
 383     run_test("frames", test_frame)
 384     run_test("finalizers", test_finalizer)
 385     run_test("finalizers (new class)", test_finalizer_newclass)
 386     run_test("__del__", test_del)
 387     run_test("__del__ (new class)", test_del_newclass)
 388     run_test("saveall", test_saveall)
 389     run_test("trashcan", test_trashcan)
 390     run_test("boom", test_boom)
 391     run_test("boom2", test_boom2)
 392     run_test("boom_new", test_boom_new)
 393     run_test("boom2_new", test_boom2_new)
 394     run_test("get_referents", test_get_referents)
 395
 396 def test():
 397     if verbose:
 398         print "disabling automatic collection"
 399     enabled = gc.isenabled()
 400     gc.disable()
 401     verify(not gc.isenabled())
 402     debug = gc.get_debug()
 403     gc.set_debug(debug & ~gc.DEBUG_LEAK) # this test is supposed to leak
 404
 405     try:
 406         test_all()
 407     finally:
 408         gc.set_debug(debug)
 409         # test gc.enable() even if GC is disabled by default
 410         if verbose:
 411             print "restoring automatic collection"
 412         # make sure to always test gc.enable()
 413         gc.enable()
 414         verify(gc.isenabled())
 415         if not enabled:
 416             gc.disable()
 417
 418
 419 test()