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,
                          import_module)
from test.support.script_helper import assert_python_ok, make_script

import gc
import sys
import sysconfig
import textwrap
import threading
import time
import weakref

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

if sysconfig.get_config_vars().get('PY_CFLAGS', ''):
    BUILD_WITH_NDEBUG = ('-DNDEBUG' in sysconfig.get_config_vars()['PY_CFLAGS'])
else:
    # Usually, sys.gettotalrefcount() is only present if Python has been
    # compiled in debug mode. If it's missing, expect that Python has
    # been released in release mode: with NDEBUG defined.
    BUILD_WITH_NDEBUG = (not hasattr(sys, 'gettotalrefcount'))

### 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