Re: [asio-users] this vs shared_from_this() in examples

[Amir T. <zg...@ya...>]

OK thanks Igor and Yuri. I understand now.

Basically io_service::stop() or the io_service must go out of scope before the class destructor (for which the methods are bound) is called. That ensures no methods tried to get call with a destroyed object.

________________________________
From: Igor R <boo...@gm...>
To: Amir Taaki <zg...@ya...>; asi...@li... 
Sent: Tuesday, February 21, 2012 10:07 AM
Subject: Re: [asio-users] this vs shared_from_this() in examples

> In my project ( http://gitorious.org/libbitcoin/libbitcoin ), I just
> realised today I have a problem with circular references. When I started,
> someone advised me to just use shared_ptr for bind and never use this.
> Assuming asio is fine with this, I didn't question that logic. However now
> I'm checking and seeing my destructors never get called.
>
> Looking through the boost asio examples, I see bind is used with this and
> shared_from_this() variously. I cannot see any pattern to it? What are the
> rules of thumb for when to use this? Why can I not just use this for
> everything? Would you pass this to std::bind when you know that the
> primitives inside it (like the strand if you're using strand post) are
> destroyed before the class?
>
> What happens then when I use strand.wrap(std::bind(&foo::memfunc, this, ...)) and pass that elsewhere?


The question is how you ensure that the object bound to your
completion handler will outlive the async operation.
Binding shared_ptr to "this" is the most simple and robust way to
provide such guarantee in a complex design, but in some trivial cases
it can be unnecessary -- these are probably the cases you saw in asio
examples.
As for circular references, this issue is usually solved by means of
using weak_ptr in one direction.