CODEWITHSUNDEEP
c++memory-managementunique-ptr
Tony The Lion
Tony The Lion

Reputation: 63310

Custom Unique_ptr deleter, controlled deleting

I have a for loop that iterates through an XML document and finds a specified attribute, the pointer that points to the current node sits inside a boost::interprocess::unique_ptr and has a custom deletor to call the object's release() function. It seems that on every loop iteration the pointer gets deleted, but the release() function throws when that happens.

Could anyone suggest a solution? I thought about implementing a mechanism to check if it should be deleted, but I'm not sure how I'd do that...

Code:

typedef bi::unique_ptr<DOMNodeIterator, release_deleter> iterator_ptr;
typedef bi::unique_ptr<DOMNode, release_deleter> node_ptr;

iterator_ptr itera(document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true));

for(node_ptr current(itera->nextNode()); current != 0; current.reset(itera->nextNode())) // throws after one iteration...
{

....

objects release() 

void DOMElementNSImpl::release()
{
    if (fNode.isOwned() && !fNode.isToBeReleased())
        throw DOMException(DOMException::INVALID_ACCESS_ERR,0, GetDOMNodeMemoryManager);  // throws here if released after each loop iteration

    DOMDocumentImpl* doc = (DOMDocumentImpl*) fParent.fOwnerDocument;
    if (doc) {
        fNode.callUserDataHandlers(DOMUserDataHandler::NODE_DELETED, 0, 0);
        fParent.release();
        doc->release(this, DOMMemoryManager::ELEMENT_NS_OBJECT);
    }
    else {
        // shouldn't reach here
        throw DOMException(DOMException::INVALID_ACCESS_ERR,0, GetDOMNodeMemoryManager);
    }
}

deleter:

struct release_deleter
{
    template <typename T>
    void operator()(T* pPtr) const
    {
        pPtr->release();
    }
};

EDIT:

virtual DOMNodeIterator *createNodeIterator(DOMNode* root,
                                            DOMNodeFilter::ShowType whatToShow,
                                            DOMNodeFilter* filter,
                                            bool entityReferenceExpansion) = 0;


virtual DOMNode*           nextNode() = 0;

Upvotes: 1

Views: 2774

Answers (1)

Stephane Rolland
Stephane Rolland

Reputation: 39926

I don't have visual 2010 for compiling and debugging at work, on ly at home. so I cannot be sure.

But Frankly I really do not like the concept that your iterator owns your pointer.

Your collection owns the pointer, the iterator doesn't ! its not its role..

In C++0x there are an complement to shared_ptr that is std::weak_ptr that you can construct from shared_ptr , allowing to consult and change the data, but having nothing to do with ownership, except becoming more or less inaccessible when the pointer onwed by the shared_ptr is released.

I would use a sort of std::weak_ptr for your iterators. But for unique_ptr I would guess it is a simple pointer over your data that takes the role of weak reference.

EDIT:

DOMNodeIterator * pIter = document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true);

if(pIter==NULL)
{
    return;
}

while(true) // be careful to infinite loops
{
    DOMNode * pNode = pIter->nextNode();
    if (pNode==NULL)
    {
        break;  
    }

    // ... your visiting the nodes here.
}

Upvotes: 2

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