C++ PolyObject::ContainsForwardingPtr方法代码示例

void ScanAddress::ScanAddressesInRegion(PolyWord *region, PolyWord *end)
{
    PolyWord *pt = region;
    while (pt < end)
    {
        pt++; // Skip length word.
        // pt actually points AT the object here.
        PolyObject *obj = (PolyObject*)pt;
        if (obj->ContainsForwardingPtr())    /* skip over moved object */
        {
            // We can now get multiple forwarding pointers as a result
            // of applying ShareData repeatedly.  Perhaps we should
            // turn the forwarding pointers back into normal words in
            // an extra pass.
            while (obj->ContainsForwardingPtr())
                obj = obj->GetForwardingPtr();
            ASSERT(obj->ContainsNormalLengthWord());
            CheckObject(obj);
            pt += obj->Length();
        }
        else
        {
            ASSERT(obj->ContainsNormalLengthWord());
            POLYUNSIGNED length = obj->Length();
            if (pt+length > end)
                Crash("Malformed object at %p - length %lu\n", pt, length);
            if (length != 0)
                ScanAddressesInObject(obj);
            pt += length;
        }
    }
}

// Returns the new address if the argument is the address of an object that
// has moved, otherwise returns the original.
PolyWord SaveFixupAddress::GetNewAddress(PolyWord old)
{
    if (old.IsTagged() || old == PolyWord::FromUnsigned(0) || gMem.IsIOPointer(old.AsAddress()))
        return old; //  Nothing to do.

    // When we are updating addresses in the stack or in code segments we may have
    // code pointers.
    if (old.IsCodePtr())
    {
        // Find the start of the code segment
        PolyObject *oldObject = ObjCodePtrToPtr(old.AsCodePtr());
        // Calculate the byte offset of this value within the code object.
        POLYUNSIGNED offset = old.AsCodePtr() - (byte*)oldObject;
        PolyWord newObject = GetNewAddress(oldObject);
        return PolyWord::FromCodePtr(newObject.AsCodePtr() + offset);
    }

    ASSERT(old.IsDataPtr());

    PolyObject *obj = old.AsObjPtr();
    
    if (obj->ContainsForwardingPtr()) // tombstone is a pointer to a moved object
    {
        PolyObject *newp = obj->GetForwardingPtr();
        ASSERT (newp->ContainsNormalLengthWord());
        return newp;
    }
    
    ASSERT (obj->ContainsNormalLengthWord()); // object is not moved
    return old;
}

// Tests if this needs to be scanned.  It marks it if it has not been marked
// unless it has to be scanned.
bool MTGCProcessMarkPointers::TestForScan(PolyWord *pt)
{
    if ((*pt).IsTagged())
        return false;

    // This could contain a forwarding pointer if it points into an
    // allocation area and has been moved by the minor GC.
    // We have to be a little careful.  Another thread could also
    // be following any forwarding pointers here.  However it's safe
    // because they will update it with the same value.
    PolyObject *obj = (*pt).AsObjPtr();
    if (obj->ContainsForwardingPtr())
    {
        obj = FollowForwarding(obj);
        *pt = obj;
    }

    if (gMem.LocalSpaceForAddress(obj) == 0)
        return false; // Ignore it if it points to a permanent area

    POLYUNSIGNED L = obj->LengthWord();
    if (L & _OBJ_GC_MARK)
        return false; // Already marked

    if (debugOptions & DEBUG_GC_DETAIL)
        Log("GC: Mark: %p %" POLYUFMT " %u\n", obj, OBJ_OBJECT_LENGTH(L), GetTypeBits(L));

    if (OBJ_IS_BYTE_OBJECT(L))
    {
        obj->SetLengthWord(L | _OBJ_GC_MARK); // Mark it
        return false; // We've done as much as we need
    }
    return true;
}

bool GetSharing::TestForScan(PolyWord *pt)
{
    PolyObject *obj;

    // This may be a forwarding pointer left over from a minor GC that did
    // not complete or it may be a sharing chain pointer that we've set up.
    while (1)
    {
        PolyWord p = *pt;
        ASSERT(p.IsDataPtr());
        obj = p.AsObjPtr();
        PolyWord *lengthWord = ((PolyWord*)obj) - 1;
        LocalMemSpace *space = gMem.LocalSpaceForAddress(lengthWord);
        if (space == 0)
            return false; // Ignore it if it points to a permanent area

        if (space->bitmap.TestBit(space->wordNo(lengthWord)))
            return false;

        // Wasn't marked - must be a forwarding pointer.
        if (obj->ContainsForwardingPtr())
        {
            obj = obj->GetForwardingPtr();
            *pt = obj;
        }
        else break;
    }

    ASSERT(obj->ContainsNormalLengthWord());

    totalVisited += 1;
    totalSize += obj->Length() + 1;

    return true;
}

static void SetBitmaps(LocalMemSpace *space, PolyWord *pt, PolyWord *top)
{
    while (pt < top)
    {
        PolyObject *obj = (PolyObject*)++pt;
        // If it has been copied by a minor collection skip it
        if (obj->ContainsForwardingPtr())
        {
            obj = FollowForwarding(obj);
            ASSERT(obj->ContainsNormalLengthWord());
            pt += obj->Length();
        }
        else
        {
            POLYUNSIGNED L = obj->LengthWord();
            POLYUNSIGNED n = OBJ_OBJECT_LENGTH(L);
            if (L & _OBJ_GC_MARK)
            {
                obj->SetLengthWord(L & ~(_OBJ_GC_MARK));
                POLYUNSIGNED bitno = space->wordNo(pt);
                space->bitmap.SetBits(bitno - 1, n + 1);

                if (OBJ_IS_MUTABLE_OBJECT(L))
                    space->m_marked += n + 1;
                else
                    space->i_marked += n + 1;

                if ((PolyWord*)obj <= space->fullGCLowerLimit)
                    space->fullGCLowerLimit = (PolyWord*)obj-1;

                if (OBJ_IS_WEAKREF_OBJECT(L))
                {
                    // Add this to the limits for the containing area.
                    PolyWord *baseAddr = (PolyWord*)obj;
                    PolyWord *startAddr = baseAddr-1; // Must point AT length word.
                    PolyWord *endObject = baseAddr + n;
                    if (startAddr < space->lowestWeak) space->lowestWeak = startAddr;
                    if (endObject > space->highestWeak) space->highestWeak = endObject;
                }
            }
            pt += n;
        }
    }
}

// Returns the new address if the argument is the address of an object that
// has moved, otherwise returns the original.
PolyWord ProcessFixupAddress::GetNewAddress(PolyWord old)
{
    if (old.IsTagged() || old == PolyWord::FromUnsigned(0) || gMem.IsIOPointer(old.AsAddress()))
        return old; //  Nothing to do.

    // When we are updating addresses in the stack or in code segments we may have
    // code pointers.
    if (old.IsCodePtr())
    {
        // Find the start of the code segment
        PolyObject *oldObject = ObjCodePtrToPtr(old.AsCodePtr());
        // Calculate the byte offset of this value within the code object.
        POLYUNSIGNED offset = old.AsCodePtr() - (byte*)oldObject;
        PolyWord newObject = GetNewAddress(oldObject);
        return PolyWord::FromCodePtr(newObject.AsCodePtr() + offset);
    }

    ASSERT(old.IsDataPtr());

    PolyObject *obj = old.AsObjPtr();
    POLYUNSIGNED L = obj->LengthWord();

    // Generally each address will point to an object processed at a lower depth.
    // The exception is if we have a cycle and have assigned the rest of the
    // structure to a higher depth.
    // N.B. We return the original address here but this could actually share
    // with something else and not be retained.
    if (OBJ_IS_DEPTH(L))
        return old;

    if (obj->ContainsForwardingPtr()) // tombstone is a pointer to a shared object
    {
        PolyObject *newp = obj->GetForwardingPtr();
//        ASSERT (newp->ContainsNormalLengthWord());
        return newp;
    }

    ASSERT (obj->ContainsNormalLengthWord()); // object is not shared
    return old;
}