Question

I got a problem when I tried to create and delete an instance of the class in a loop.
Execution time of iterations is quite different. As I understand it, this is associated with the removal of objects from memory. However, the behavior of this operation I do not understand. Why time is different? How do I fix it? Time is steady when I’m deleting the object in a separate thread.

class NODE{

    public:
        NODE(){}

        NODE* add(NODE* node)
        {
            children.push_back(node);
            return node;
        }

        virtual ~NODE()
        {
            for(vector<NODE*>::iterator it = children.begin(); it != children.end(); ++it)
            {
                delete *it;
            }
        }

        vector<NODE*> children;

};

NODE* create()
{
    NODE* node( new NODE() );

    for (int i=0; i<200;i++) {
        NODE* subnode = node->add( new NODE());
        for (int k=0; k<20; k++) subnode->add( new NODE());
    }

    return node;
}

int main()
{
    NODE* root;
    unsigned t;

    for (int i=0; i<30; i++){
        t = clock();
        cout << "Create... ";
        root = create();
        delete root;
        cout<< clock()-t << endl;
    }
}

ADDED:
I’m confused. When I run program out of VS it works fine…

Answer 1

In addition to what other answers say you have to account for Visual C++ 10 runtime heap being thread-safe. This implies that even when you only have one thread you encounter some overhead facilitating heap operations being thread-safe. So one reason you see such poor results is that you use a universal but rather slow heap implementation.

The reason why you get different timing with/without the debugger is a special heap is used when a program is started under debugger (even in Release configuration) and that special heap is also relatively slow.