/rpython/memory/gc/test/test_direct.py

""" The tests below don't use translation at all.  They run the GCs by
instantiating them and asking them to allocate memory by calling their
methods directly.  The tests need to maintain by hand what the GC should
see as the list of roots (stack and prebuilt objects).
"""

# XXX VERY INCOMPLETE, low coverage

import py
from rpython.rtyper.lltypesystem import lltype, llmemory
from rpython.memory.gctypelayout import TypeLayoutBuilder, FIN_HANDLER_ARRAY
from rpython.rlib.rarithmetic import LONG_BIT, is_valid_int
from rpython.memory.gc import minimark, incminimark
from rpython.memory.gctypelayout import zero_gc_pointers_inside, zero_gc_pointers
from rpython.rlib.debug import debug_print
import pdb
WORD = LONG_BIT // 8

ADDR_ARRAY = lltype.Array(llmemory.Address)
S = lltype.GcForwardReference()
S.become(lltype.GcStruct('S',
                         ('x', lltype.Signed),
                         ('prev', lltype.Ptr(S)),
                         ('next', lltype.Ptr(S))))
RAW = lltype.Struct('RAW', ('p', lltype.Ptr(S)), ('q', lltype.Ptr(S)))
VAR = lltype.GcArray(lltype.Ptr(S))
VARNODE = lltype.GcStruct('VARNODE', ('a', lltype.Ptr(VAR)))


class DirectRootWalker(object):

    def __init__(self, tester):
        self.tester = tester

    def walk_roots(self, collect_stack_root,
                   collect_static_in_prebuilt_nongc,
                   collect_static_in_prebuilt_gc,
                   is_minor=False):
        gc = self.tester.gc
        layoutbuilder = self.tester.layoutbuilder
        if collect_static_in_prebuilt_gc:
            for addrofaddr in layoutbuilder.addresses_of_static_ptrs:
                if addrofaddr.address[0]:
                    collect_static_in_prebuilt_gc(gc, addrofaddr)
        if collect_static_in_prebuilt_nongc:
            for addrofaddr in layoutbuilder.addresses_of_static_ptrs_in_nongc:
                if addrofaddr.address[0]:
                    collect_static_in_prebuilt_nongc(gc, addrofaddr)
        if collect_stack_root:
            stackroots = self.tester.stackroots
            a = lltype.malloc(ADDR_ARRAY, len(stackroots), flavor='raw')
            for i in range(len(a)):
                a[i] = llmemory.cast_ptr_to_adr(stackroots[i])
            a_base = lltype.direct_arrayitems(a)
            for i in range(len(a)):
                ai = lltype.direct_ptradd(a_base, i)
                collect_stack_root(gc, llmemory.cast_ptr_to_adr(ai))
            for i in range(len(a)):
                PTRTYPE = lltype.typeOf(stackroots[i])
                stackroots[i] = llmemory.cast_adr_to_ptr(a[i], PTRTYPE)
            lltype.free(a, flavor='raw')

    def _walk_prebuilt_gc(self, callback):
        pass

    def finished_minor_collection(self):
        pass


class BaseDirectGCTest(object):
    GC_PARAMS = {}

    def setup_method(self, meth):
        from rpython.config.translationoption import get_combined_translation_config
        config = get_combined_translation_config(translating=True).translation
        self.stackroots = []
        GC_PARAMS = self.GC_PARAMS.copy()
        if hasattr(meth, 'GC_PARAMS'):
            GC_PARAMS.update(meth.GC_PARAMS)
        GC_PARAMS['translated_to_c'] = False
        self.gc = self.GCClass(config, **GC_PARAMS)
        self.gc.DEBUG = True
        self.rootwalker = DirectRootWalker(self)
        self.gc.set_root_walker(self.rootwalker)
        self.layoutbuilder = TypeLayoutBuilder(self.GCClass)
        self.get_type_id = self.layoutbuilder.get_type_id
        gcdata = self.layoutbuilder.initialize_gc_query_function(self.gc)
        ll_handlers = lltype.malloc(FIN_HANDLER_ARRAY, 0, immortal=True)
        gcdata.finalizer_handlers = llmemory.cast_ptr_to_adr(ll_handlers)
        self.gc.setup()

    def consider_constant(self, p):
        obj = p._obj
        TYPE = lltype.typeOf(obj)
        self.layoutbuilder.consider_constant(TYPE, obj, self.gc)

    def write(self, p, fieldname, newvalue):
        if self.gc.needs_write_barrier:
            addr_struct = llmemory.cast_ptr_to_adr(p)
            self.gc.write_barrier(addr_struct)
        setattr(p, fieldname, newvalue)

    def writearray(self, p, index, newvalue):
        if self.gc.needs_write_barrier:
            addr_struct = llmemory.cast_ptr_to_adr(p)
            if hasattr(self.gc, 'write_barrier_from_array'):
                self.gc.write_barrier_from_array(addr_struct, index)
            else:
                self.gc.write_barrier(addr_struct)
        p[index] = newvalue

    def malloc(self, TYPE, n=None):
        addr = self.gc.malloc(self.get_type_id(TYPE), n)
        debug_print(self.gc)
        obj_ptr = llmemory.cast_adr_to_ptr(addr, lltype.Ptr(TYPE))
        if not self.gc.malloc_zero_filled:
            zero_gc_pointers_inside(obj_ptr, TYPE)
        return obj_ptr


class DirectGCTest(BaseDirectGCTest):
    
    def test_simple(self):
        p = self.malloc(S)
        p.x = 5
        self.stackroots.append(p)
        self.gc.collect()
        p = self.stackroots[0]
        assert p.x == 5

    def test_missing_stack_root(self):
        p = self.malloc(S)
        p.x = 5
        self.gc.collect()    # 'p' should go away
        py.test.raises(RuntimeError, 'p.x')

    def test_prebuilt_gc(self):
        k = lltype.malloc(S, immortal=True)
        k.x = 42
        self.consider_constant(k)
        self.write(k, 'next', self.malloc(S))
        k.next.x = 43
        self.write(k.next, 'next', self.malloc(S))
        k.next.next.x = 44
        self.gc.collect()
        assert k.x == 42
        assert k.next.x == 43
        assert k.next.next.x == 44

    def test_prebuilt_nongc(self):
        raw = lltype.malloc(RAW, immortal=True)
        self.consider_constant(raw)
        raw.p = self.malloc(S)
        raw.p.x = 43
        raw.q = self.malloc(S)
        raw.q.x = 44
        self.gc.collect()
        assert raw.p.x == 43
        assert raw.q.x == 44

    def test_many_objects(self):

        def alloc2(i):
            a1 = self.malloc(S)
            a1.x = i
            self.stackroots.append(a1)
            a2 = self.malloc(S)
            a1 = self.stackroots.pop()
            a2.x = i + 1000
            return a1, a2

        def growloop(loop, a1, a2):
            self.write(a1, 'prev', loop.prev)
            self.write(a1.prev, 'next', a1)
            self.write(a1, 'next', loop)
            self.write(loop, 'prev', a1)
            self.write(a2, 'prev', loop)
            self.write(a2, 'next', loop.next)
            self.write(a2.next, 'prev', a2)
            self.write(loop, 'next', a2)

        def newloop():
            p = self.malloc(S)
            p.next = p          # initializing stores, no write barrier
            p.prev = p
            return p

        # a loop attached to a stack root
        self.stackroots.append(newloop())

        # another loop attached to a prebuilt gc node
        k = lltype.malloc(S, immortal=True)
        k.next = k
        k.prev = k
        self.consider_constant(k)

        # a third loop attached to a prebuilt nongc
        raw = lltype.malloc(RAW, immortal=True)
        self.consider_constant(raw)
        raw.p = newloop()

        # run!
        for i in range(100):
            a1, a2 = alloc2(i)
            growloop(self.stackroots[0], a1, a2)
            a1, a2 = alloc2(i)
            growloop(k, a1, a2)
            a1, a2 = alloc2(i)
            growloop(raw.p, a1, a2)

    def test_varsized_from_stack(self):
        expected = {}
        def verify():
            for (index, index2), value in expected.items():
                assert self.stackroots[index][index2].x == value
        x = 0
        for i in range(40):
            assert 'DEAD' not in repr(self.stackroots)
            a = self.malloc(VAR, i)
            assert 'DEAD' not in repr(a)
            self.stackroots.append(a)
            print 'ADDED TO STACKROOTS:', llmemory.cast_adr_to_int(
                llmemory.cast_ptr_to_adr(a))
            assert 'DEAD' not in repr(self.stackroots)
            for j in range(5):
                assert 'DEAD' not in repr(self.stackroots)
                p = self.malloc(S)
                assert 'DEAD' not in repr(self.stackroots)
                p.x = x
                index = x % len(self.stackroots)
                if index > 0:
                    index2 = (x / len(self.stackroots)) % index
                    a = self.stackroots[index]
                    assert len(a) == index
                    self.writearray(a, index2, p)
                    expected[index, index2] = x
                x += 1291
        verify()
        self.gc.collect()
        verify()
        self.gc.collect()
        verify()

    def test_varsized_from_prebuilt_gc(self):
        expected = {}
        def verify():
            for (index, index2), value in expected.items():
                assert prebuilt[index].a[index2].x == value
        x = 0
        prebuilt = [lltype.malloc(VARNODE, immortal=True, zero=True)
                    for i in range(40)]
        for node in prebuilt:
            self.consider_constant(node)
        for i in range(len(prebuilt)):
            self.write(prebuilt[i], 'a', self.malloc(VAR, i))
            for j in range(20):
                p = self.malloc(S)
                p.x = x
                index = x % (i+1)
                if index > 0:
                    index2 = (x / (i+1)) % index
                    a = prebuilt[index].a
                    assert len(a) == index
                    self.writearray(a, index2, p)
                    expected[index, index2] = x
                x += 1291
        verify()
        self.gc.collect()
        verify()
        self.gc.collect()
        verify()

    def test_id(self):
        ids = {}
        def allocate_bunch(count=50):
            base = len(self.stackroots)
            for i in range(count):
                p = self.malloc(S)
                self.stackroots.append(p)
            for i in range(count):
                j = base + (i*1291) % count
                pid = self.gc.id(self.stackroots[j])
                assert isinstance(pid, int)
                ids[j] = pid
        def verify():
            for j, expected in ids.items():
                assert self.gc.id(self.stackroots[j]) == expected
        allocate_bunch(5)
        verify()
        allocate_bunch(75)
        verify()
        allocate_bunch(5)
        verify()
        self.gc.collect()
        verify()
        self.gc.collect()
        verify()

    def test_identityhash(self):
        # a "does not crash" kind of test
        p_const = lltype.malloc(S, immortal=True)
        self.consider_constant(p_const)
        # (1) p is in the nursery
        self.gc.collect()
        p = self.malloc(S)
        hash = self.gc.identityhash(p)
        print hash
        assert is_valid_int(hash)
        assert hash == self.gc.identityhash(p)
        self.stackroots.append(p)
        for i in range(6):
            self.gc.collect()
            assert hash == self.gc.identityhash(self.stackroots[-1])
        self.stackroots.pop()
        # (2) p is an older object
        p = self.malloc(S)
        self.stackroots.append(p)
        self.gc.collect()
        hash = self.gc.identityhash(self.stackroots[-1])
        print hash
        assert is_valid_int(hash)
        for i in range(6):
            self.gc.collect()
            assert hash == self.gc.identityhash(self.stackroots[-1])
        self.stackroots.pop()
        # (3) p is a gen3 object (for hybrid)
        p = self.malloc(S)
        self.stackroots.append(p)
        for i in range(6):
            self.gc.collect()
        hash = self.gc.identityhash(self.stackroots[-1])
        print hash
        assert is_valid_int(hash)
        for i in range(2):
            self.gc.collect()
            assert hash == self.gc.identityhash(self.stackroots[-1])
        self.stackroots.pop()
        # (4) p is a prebuilt object
        hash = self.gc.identityhash(p_const)
        print hash
        assert is_valid_int(hash)
        assert hash == self.gc.identityhash(p_const)
        # (5) p is actually moving (for the markcompact gc only?)
        p0 = self.malloc(S)
        self.stackroots.append(p0)
        p = self.malloc(S)
        self.stackroots.append(p)
        hash = self.gc.identityhash(p)
        self.stackroots.pop(-2)
        self.gc.collect()     # p0 goes away, p shifts left
        assert hash == self.gc.identityhash(self.stackroots[-1])
        self.gc.collect()
        assert hash == self.gc.identityhash(self.stackroots[-1])
        self.stackroots.pop()
        # (6) ask for the hash of varsized objects, larger and larger
        for i in range(10):
            self.gc.collect()
            p = self.malloc(VAR, i)
            self.stackroots.append(p)
            hash = self.gc.identityhash(p)
            self.gc.collect()
            assert hash == self.gc.identityhash(self.stackroots[-1])
            self.stackroots.pop()
        # (7) the same, but the objects are dying young
        for i in range(10):
            self.gc.collect()
            p = self.malloc(VAR, i)
            self.stackroots.append(p)
            hash1 = self.gc.identityhash(p)
            hash2 = self.gc.identityhash(p)
            assert hash1 == hash2
            self.stackroots.pop()

    def test_memory_alignment(self):
        A1 = lltype.GcArray(lltype.Char)
        for i in range(50):
            p1 = self.malloc(A1, i)
            if i:
                p1[i-1] = chr(i)
            self.stackroots.append(p1)
        self.gc.collect()
        for i in range(1, 50):
            p = self.stackroots[-50+i]
            assert p[i-1] == chr(i)

class TestSemiSpaceGC(DirectGCTest):
    from rpython.memory.gc.semispace import SemiSpaceGC as GCClass

    def test_shrink_array(self):
        S1 = lltype.GcStruct('S1', ('h', lltype.Char),
                                   ('v', lltype.Array(lltype.Char)))
        p1 = self.malloc(S1, 2)
        p1.h = '?'
        for i in range(2):
            p1.v[i] = chr(50 + i)
        addr = llmemory.cast_ptr_to_adr(p1)
        ok = self.gc.shrink_array(addr, 1)
        assert ok
        assert p1.h == '?'
        assert len(p1.v) == 1
        for i in range(1):
            assert p1.v[i] == chr(50 + i)


class TestGenerationGC(TestSemiSpaceGC):
    from rpython.memory.gc.generation import GenerationGC as GCClass

    def test_collect_gen(self):
        gc = self.gc
        old_semispace_collect = gc.semispace_collect
        old_collect_nursery = gc.collect_nursery
        calls = []
        def semispace_collect():
            calls.append('semispace_collect')
            return old_semispace_collect()
        def collect_nursery():
            calls.append('collect_nursery')
            return old_collect_nursery()
        gc.collect_nursery = collect_nursery
        gc.semispace_collect = semispace_collect

        gc.collect()
        assert calls == ['semispace_collect']
        calls = []

        gc.collect(0)
        assert calls == ['collect_nursery']
        calls = []

        gc.collect(1)
        assert calls == ['semispace_collect']
        calls = []

        gc.collect(9)
        assert calls == ['semispace_collect']
        calls = []

    def test_write_barrier_direct(self):
        s0 = lltype.malloc(S, immortal=True)
        self.consider_constant(s0)
        s = self.malloc(S)
        s.x = 1
        s0.next = s
        self.gc.write_barrier(llmemory.cast_ptr_to_adr(s0))

        self.gc.collect(0)

        assert s0.next.x == 1


class TestHybridGC(TestGenerationGC):
    from rpython.memory.gc.hybrid import HybridGC as GCClass

    GC_PARAMS = {'space_size': 48*WORD,
                 'min_nursery_size': 12*WORD,
                 'nursery_size': 12*WORD,
                 'large_object': 3*WORD,
                 'large_object_gcptrs': 3*WORD,
                 'generation3_collect_threshold': 5,
                 }

    def test_collect_gen(self):
        gc = self.gc
        old_semispace_collect = gc.semispace_collect
        old_collect_nursery = gc.collect_nursery
        calls = []
        def semispace_collect():
            gen3 = gc.is_collecting_gen3()
            calls.append(('semispace_collect', gen3))
            return old_semispace_collect()
        def collect_nursery():
            calls.append('collect_nursery')
            return old_collect_nursery()
        gc.collect_nursery = collect_nursery
        gc.semispace_collect = semispace_collect

        gc.collect()
        assert calls == [('semispace_collect', True)]
        calls = []

        gc.collect(0)
        assert calls == ['collect_nursery']
        calls = []

        gc.collect(1)
        assert calls == [('semispace_collect', False)]
        calls = []

        gc.collect(2)
        assert calls == [('semispace_collect', True)]
        calls = []

        gc.collect(9)
        assert calls == [('semispace_collect', True)]
        calls = []

    def test_identityhash(self):
        py.test.skip("does not support raw_mallocs(sizeof(S)+sizeof(hash))")


class TestMiniMarkGCSimple(DirectGCTest):
    from rpython.memory.gc.minimark import MiniMarkGC as GCClass
    from rpython.memory.gc.minimarktest import SimpleArenaCollection
    # test the GC itself, providing a simple class for ArenaCollection
    GC_PARAMS = {'ArenaCollectionClass': SimpleArenaCollection}

    def test_card_marker(self):
        for arraylength in (range(4, 17)
                            + [69]      # 3 bytes
                            + [300]):   # 10 bytes
            print 'array length:', arraylength
            nums = {}
            a = self.malloc(VAR, arraylength)
            self.stackroots.append(a)
            for i in range(50):
                p = self.malloc(S)
                p.x = -i
                a = self.stackroots[-1]
                index = (i*i) % arraylength
                self.writearray(a, index, p)
                nums[index] = p.x
                #
                for index, expected_x in nums.items():
                    assert a[index].x == expected_x
            self.stackroots.pop()
    test_card_marker.GC_PARAMS = {"card_page_indices": 4}

    def test_writebarrier_before_copy(self):
        largeobj_size =  self.gc.nonlarge_max + 1
        self.gc.next_major_collection_threshold = 99999.0
        p_src = self.malloc(VAR, largeobj_size)
        p_dst = self.malloc(VAR, largeobj_size)
        # make them old
        self.stackroots.append(p_src)
        self.stackroots.append(p_dst)
        self.gc.collect()
        p_dst = self.stackroots.pop()
        p_src = self.stackroots.pop()
        #
        addr_src = llmemory.cast_ptr_to_adr(p_src)
        addr_dst = llmemory.cast_ptr_to_adr(p_dst)
        hdr_src = self.gc.header(addr_src)
        hdr_dst = self.gc.header(addr_dst)
        #
        assert hdr_src.tid & minimark.GCFLAG_TRACK_YOUNG_PTRS
        assert hdr_dst.tid & minimark.GCFLAG_TRACK_YOUNG_PTRS
        #
        res = self.gc.writebarrier_before_copy(addr_src, addr_dst, 0, 0, 10)
        assert res
        assert hdr_dst.tid & minimark.GCFLAG_TRACK_YOUNG_PTRS
        #
        hdr_src.tid &= ~minimark.GCFLAG_TRACK_YOUNG_PTRS  # pretend we have young ptrs
        res = self.gc.writebarrier_before_copy(addr_src, addr_dst, 0, 0, 10)
        assert res # we optimized it
        assert hdr_dst.tid & minimark.GCFLAG_TRACK_YOUNG_PTRS == 0 # and we copied the flag
        #
        self.gc.card_page_indices = 128     # force > 0
        hdr_src.tid |= minimark.GCFLAG_TRACK_YOUNG_PTRS
        hdr_dst.tid |= minimark.GCFLAG_TRACK_YOUNG_PTRS
        hdr_src.tid |= minimark.GCFLAG_HAS_CARDS
        hdr_src.tid |= minimark.GCFLAG_CARDS_SET
        # hdr_dst.tid does not have minimark.GCFLAG_HAS_CARDS
        res = self.gc.writebarrier_before_copy(addr_src, addr_dst, 0, 0, 10)
        assert not res # there might be young ptrs, let ll_arraycopy to find them

    def test_writebarrier_before_copy_preserving_cards(self):
        from rpython.rtyper.lltypesystem import llarena
        tid = self.get_type_id(VAR)
        largeobj_size =  self.gc.nonlarge_max + 1
        self.gc.next_major_collection_threshold = 99999.0
        addr_src = self.gc.external_malloc(tid, largeobj_size, alloc_young=True)
        addr_dst = self.gc.external_malloc(tid, largeobj_size, alloc_young=True)
        hdr_src = self.gc.header(addr_src)
        hdr_dst = self.gc.header(addr_dst)
        #
        assert hdr_src.tid & minimark.GCFLAG_HAS_CARDS
        assert hdr_dst.tid & minimark.GCFLAG_HAS_CARDS
        #
        self.gc.write_barrier_from_array(addr_src, 0)
        index_in_third_page = int(2.5 * self.gc.card_page_indices)
        assert index_in_third_page < largeobj_size
        self.gc.write_barrier_from_array(addr_src, index_in_third_page)
        #
        assert hdr_src.tid & minimark.GCFLAG_CARDS_SET
        addr_byte = self.gc.get_card(addr_src, 0)
        assert ord(addr_byte.char[0]) == 0x01 | 0x04  # bits 0 and 2
        #
        res = self.gc.writebarrier_before_copy(addr_src, addr_dst,
                                             0, 0, 2*self.gc.card_page_indices)
        assert res
        #
        assert hdr_dst.tid & minimark.GCFLAG_CARDS_SET
        addr_byte = self.gc.get_card(addr_dst, 0)
        assert ord(addr_byte.char[0]) == 0x01 | 0x04  # bits 0 and 2

    test_writebarrier_before_copy_preserving_cards.GC_PARAMS = {
        "card_page_indices": 4}


class TestMiniMarkGCFull(DirectGCTest):
    from rpython.memory.gc.minimark import MiniMarkGC as GCClass

class TestIncrementalMiniMarkGCSimple(TestMiniMarkGCSimple):
    from rpython.memory.gc.incminimark import IncrementalMiniMarkGC as GCClass

    def test_write_barrier_marking_simple(self):
        for i in range(2):
            curobj = self.malloc(S)
            curobj.x = i
            self.stackroots.append(curobj)


        oldobj = self.stackroots[-1]
        oldhdr = self.gc.header(llmemory.cast_ptr_to_adr(oldobj))

        assert oldhdr.tid & incminimark.GCFLAG_VISITED == 0
        self.gc.debug_gc_step_until(incminimark.STATE_MARKING)
        oldobj = self.stackroots[-1]
        # object shifted by minor collect
        oldhdr = self.gc.header(llmemory.cast_ptr_to_adr(oldobj))
        assert oldhdr.tid & incminimark.GCFLAG_VISITED == 0

        self.gc._minor_collection()
        self.gc.visit_all_objects_step(1)

        assert oldhdr.tid & incminimark.GCFLAG_VISITED

        #at this point the first object should have been processed
        newobj = self.malloc(S)
        self.write(oldobj,'next',newobj)

        assert self.gc.header(self.gc.old_objects_pointing_to_young.tolist()[0]) == oldhdr

        self.gc._minor_collection()
        self.gc.debug_check_consistency()

    def test_sweeping_simple(self):
        assert self.gc.gc_state == incminimark.STATE_SCANNING

        for i in range(2):
            curobj = self.malloc(S)
            curobj.x = i
            self.stackroots.append(curobj)

        self.gc.debug_gc_step_until(incminimark.STATE_SWEEPING)
        oldobj = self.stackroots[-1]
        oldhdr = self.gc.header(llmemory.cast_ptr_to_adr(oldobj))
        assert oldhdr.tid & incminimark.GCFLAG_VISITED

        newobj1 = self.malloc(S)
        newobj2 = self.malloc(S)
        newobj1.x = 1337
        newobj2.x = 1338
        self.write(oldobj,'next',newobj1)
        self.gc.debug_gc_step_until(incminimark.STATE_SCANNING)
        #should not be cleared even though it was allocated while sweeping
        newobj1 = oldobj.next
        assert newobj1.x == 1337

    def test_obj_on_escapes_on_stack(self):
        obj0 = self.malloc(S)

        self.stackroots.append(obj0)
        obj0.next = self.malloc(S)
        self.gc.debug_gc_step_until(incminimark.STATE_MARKING)
        obj0 = self.stackroots[-1]
        obj1 = obj0.next
        obj1.x = 13
        obj0.next = lltype.nullptr(S)
        self.stackroots.append(obj1)
        self.gc.debug_gc_step_until(incminimark.STATE_SCANNING)
        assert self.stackroots[1].x == 13

class TestIncrementalMiniMarkGCFull(DirectGCTest):
    from rpython.memory.gc.incminimark import IncrementalMiniMarkGC as GCClass
    def test_malloc_fixedsize_no_cleanup(self):
        p = self.malloc(S)
        import pytest
        #ensure the memory is uninitialized
        with pytest.raises(lltype.UninitializedMemoryAccess):
            x1 = p.x
        #ensure all the ptr fields are zeroed
        assert p.prev == lltype.nullptr(S)
        assert p.next == lltype.nullptr(S)
    
    def test_malloc_varsize_no_cleanup(self):
        x = lltype.Signed
        VAR1 = lltype.GcArray(x)
        p = self.malloc(VAR1,5)
        import pytest
        with pytest.raises(lltype.UninitializedMemoryAccess):
            assert isinstance(p[0], lltype._uninitialized)
            x1 = p[0]

    def test_malloc_varsize_no_cleanup2(self):
        #as VAR is GcArray so the ptr will don't need to be zeroed
        p = self.malloc(VAR, 100)
        for i in range(100):
            assert p[i] == lltype.nullptr(S)

    def test_malloc_varsize_no_cleanup3(self):
        VAR1 = lltype.Array(lltype.Ptr(S))
        p1 = lltype.malloc(VAR1, 10, flavor='raw', track_allocation=False)
        import pytest
        with pytest.raises(lltype.UninitializedMemoryAccess):
            for i in range(10):
                assert p1[i] == lltype.nullptr(S)
                p1[i]._free()
            p1._free()

    def test_malloc_struct_of_ptr_struct(self):
        S3 = lltype.GcForwardReference()
        S3.become(lltype.GcStruct('S3',
                         ('gcptr_struct', S),
                         ('prev', lltype.Ptr(S)),
                         ('next', lltype.Ptr(S))))
        s3 = self.malloc(S3)
        assert s3.gcptr_struct.prev == lltype.nullptr(S)
        assert s3.gcptr_struct.next == lltype.nullptr(S)

    def test_malloc_array_of_ptr_struct(self):
        ARR_OF_PTR_STRUCT = lltype.GcArray(lltype.Ptr(S))
        arr_of_ptr_struct = self.malloc(ARR_OF_PTR_STRUCT,5)
        for i in range(5):
            assert arr_of_ptr_struct[i] == lltype.nullptr(S)
            assert arr_of_ptr_struct[i] == lltype.nullptr(S)
            arr_of_ptr_struct[i] = self.malloc(S)
            assert arr_of_ptr_struct[i].prev == lltype.nullptr(S)
            assert arr_of_ptr_struct[i].next == lltype.nullptr(S)

    #fail for now
    def xxx_test_malloc_array_of_ptr_arr(self):
        ARR_OF_PTR_ARR = lltype.GcArray(lltype.Ptr(lltype.GcArray(lltype.Ptr(S))))
        arr_of_ptr_arr = self.malloc(ARR_OF_PTR_ARR, 10)
        self.stackroots.append(arr_of_ptr_arr)
        for i in range(10):
            assert arr_of_ptr_arr[i] == lltype.nullptr(lltype.GcArray(lltype.Ptr(S)))
        for i in range(10):
            self.writearray(arr_of_ptr_arr, i,
                            self.malloc(lltype.GcArray(lltype.Ptr(S)), i))
            #self.stackroots.append(arr_of_ptr_arr[i])
            #debug_print(arr_of_ptr_arr[i])
            for elem in arr_of_ptr_arr[i]:
                #self.stackroots.append(elem)
                assert elem == lltype.nullptr(S)
                elem = self.malloc(S)
                assert elem.prev == lltype.nullptr(S)
                assert elem.next == lltype.nullptr(S)