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

Thanks Richard, appreciate it. On 12/26/18, Richard Hodges via Boost 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 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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