c++ - Getting a boost::shared_ptr for this

Question

I am making extensive use of boost:shared_ptr in my code. In fact, most of the objects that are allocated on the heap are held by a shared_ptr. Unfortunately this means that I can't pass this into any function that takes a shared_ptr. Consider this code:

void bar(boost::shared_ptr<Foo> pFoo)
{
    ...
}

void Foo::someFunction()
{
    bar(this);
}

There are two problems here. First, this won't compile because the T* constructor for shared_ptr is explicit. Second, if I force it to build with bar(boost::shared_ptr<Foo>(this)) I will have created a second shared pointer to my object that will eventually lead to a double-delete.

This brings me to my question: Is there any standard pattern for getting a copy of the existing shared pointer you know exists from inside a method on one of those objects? Is using intrusive reference counting my only option here?

Answer 1

You can derive from enable_shared_from_this and then you can use "shared_from_this()" instead of "this" to spawn a shared pointer to your own self object.

Example in the link:

#include <boost/enable_shared_from_this.hpp>

class Y: public boost::enable_shared_from_this<Y>
{
public:

    shared_ptr<Y> f()
    {
        return shared_from_this();
    }
}

int main()
{
    shared_ptr<Y> p(new Y);
    shared_ptr<Y> q = p->f();
    assert(p == q);
    assert(!(p < q || q < p)); // p and q must share ownership
}

It's a good idea when spawning threads from a member function to boost::bind to a shared_from_this() instead of this. It will ensure that the object is not released.