Re: [boost] Does async_accept only access connection object raw pointer and wrapped it by shared pointer internally?

Subject: Re: [boost] Does async_accept only access connection object raw pointer and wrapped it by shared pointer internally?
From: hh h (jupiter.hce_at_[hidden])
Date: 2018-12-26 21:40:38

Thanks Richard, appreciate it.

On 12/26/18, Richard Hodges via Boost <boost_at_[hidden]> wrote:
> In this example, async_accept is not accepting any raw pointer. The raw
> pointer is being bound to the handler.
>
> What you are not doing is preserving the lifetime of the session because
> you're not storing new_session anywhere.
>
> It becomes a little easier to follow if you use a lambda:
>
>
> auto new_session = std::make_shared<session>(io_service_, context_);
>
> auto handler = [new_session, this](auto ec) mutable      // 1
> {
>   // 2
>   if (ec == boost::system::error_code())  // no error
>     new_session->start();   // 3
>   else
>     this->report_error(ec);
> };
>
> acceptor_.async_accept(new_session->socket(), std::move(handler));
>
>
>
> Notes:
> 1: recent versions of asio understand rvalues and avoid copying mutable
> handlers.
> 2: note that the shared_ptr to session has been captured by the handler.
> This will keep it alive until after the handler has been invoked.
> 3. session::start would capture itself when issuing async operations on the
> socket. You would derive it from std::enable_shared_from_this<session>.
> e.g.
>
> void session::initiate_read()
> {
>   auto handler = [self = shared_from_this()](auto ec, auto
> bytes_transferred) mutable //4
>   {
>     if (ec == system::error_code())  // no error
>     {
>         self->handle_data(bytes_transferred);
>         self->initiate_read();
>     }
>     else
>       self->handle_read_error(ec);
>   };
>
>   asio::async_read_until(socket, read_buffer, '\n', std::move(handler));
> // for example
> }
>
> 4: note that we have captured the lifetime of the session before the async
> handler for async_accept has completed. Therefore we extend the lifetime of
> the session.
>
>
> On Wed, 26 Dec 2018 at 05:22, hh h via Boost <boost_at_[hidden]> wrote:
>
>> I don't like to use raw pointer by new and delete, but the following
>> code will be crashed by double delete, can't async_accept accept
>> shared pointer?
>>
>> std::shared_ptr<session> new_session =
>> std::make_shared<session>(io_service_, context_);
>> acceptor_.async_accept(new_session->socket(),
>> boost::bind(&server::handle_accept, this, new_session.get(),
>> boost::asio::placeholders::error));
>>
>> Thank you.
>>
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>
>
> --
> Richard Hodges
> hodges.r_at_[hidden]
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