Returning an iterator in a multi-threaded environment is a good idea?

Question

Is it good to return an iterator in a list in an object that is used and used in a multi-threaded environment?

class RequestList
{
public:
    RequestList::RequestList();
    RequestList::~RequestList();

    std::list<boost::shared_ptr<Request> >::iterator GetIterator();
    int ListSize();
    void AddItem(boost::shared_ptr<Request> request);
    void RemoveItem(boost::shared_ptr<Request> request);
    std::list<boost::shared_ptr<Request> > GetRequestsList();
    boost::shared_ptr<Request> GetRequest();

private:
    std::list<boost::shared_ptr<Request> > requests;
    std::list<boost::shared_ptr<Request> >::iterator iter;   //Iterator
    boost::mutex listmtx;
};




std::list<boost::shared_ptr<Request> >::iterator RequestList::GetIterator()
{
    return this->iter;
}

Using:

RequestList* requests;

In some thread (can be used again in other threads)

 std::list<boost::shared_ptr<Request> >::iterator iter = requests->GetIterator();

Or would it be wiser to just create an iterator for this list every time and use it locally inside each thread?

Answer 1

No, it is usually not recommended to share an iterator over threads. There are several ways to make sure you have no problem.

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