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Subject: Re: [boost] Should pass boost::asio::io_service by raw pointer or smart pointer?
From: Antony Polukhin (antoshkka_at_[hidden])
Date: 2018-12-26 07:01:51

On Wed, Dec 26, 2018, 06:13 Vinnie Falco via Boost <boost_at_[hidden]

> On Tue, Dec 25, 2018 at 4:54 AM Antony Polukhin via Boost
> <boost_at_[hidden]> wrote:
> > Hmmm... just double checking that my knowledge is up to date: there's no
> > way to create a timer, async wait for it and pass the ownership to the
> > callback. In other words, code like the following can not be improved in
> > C++14:
> The version of C++ has nothing to do with what is possible or how the
> asynchronous ownership model works. I/O objects need a stable address.
> After an asynchronous operation completes, it is likely that the
> operation will be repeated in the future. For example, you will likely
> read from a socket again. Therefore, your "operation" for delaying the
> execution of a single function object might look like this:
> class delayed_runner
> {
> net::steady_timer tm_;
> public:
> using clock_type = std::steady_clock;
> ...
> template <class NullaryFunction>
> NET_INITFN_RESULT_TYPE(NullaryFunction, void(void))
> async_run_after (clock_type::duration expiry_time,
> NullaryFunction&&);
> template <class NullaryFunction>
> NET_INITFN_RESULT_TYPE(NullaryFunction, void(void))
> async_run_at (clock_type::time_point expiry_time,
> NullaryFunction&&);
> void cancel();
> };
> The caller is responsible for ensuring this object is not destroyed
> while there is an outstanding operation. Similar to how a socket is
> treated, a `delayed_runner` would be a data member of some "session"
> object which is itself managed by `shared_ptr`. Completion handlers
> use a "handler owns I/O object" shared ownership model, so the
> function object contains a bound copy of the shared pointer, ensuring
> that the lifetime of the I/O object extends until the function object
> is invoked or destroyed.

Yes, thank you, I knew that.

The statement was that the ASIO classes should be stored by value. I was
wondering about the possibility of that in some cases.

The version of the C++ Standard is relevant here. C++17 added guaranteed
copy elisions and brought more order into evaluation order :) Does it allow
to make a callback with stable address and an async waiting timer in it
without a call to operator new?


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