Asio の非同期書き込みを強化してメッセージ インターリーブを防ぐにはどうすればよいですか?

#include <boost/asio.hpp>
#include <boost/bind.hpp>

#include <deque>
#include <iostream>
#include <string>

class Connection {
public:
    Connection(boost::asio::io_service& io_service)
        : _io_service(io_service), _strand(io_service), _socket(io_service), _outbox() {}

    void write(const std::string& message) {
        _strand.post(boost::bind(&Connection::writeImpl, this, message));
    }

private:
    void writeImpl(const std::string& message) {
        _outbox.push_back(message);
        if (_outbox.size() > 1) {
            // Outstanding async_write, return
            return;
        }

        this->write();
    }

    void write() {
        const std::string& message = _outbox[0];
        boost::asio::async_write(_socket, boost::asio::buffer(message.c_str(), message.size()),
                                 _strand.wrap(boost::bind(&Connection::writeHandler, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)));
    }

    void writeHandler(const boost::system::error_code& error, const size_t bytesTransferred) {
        _outbox.pop_front();

        if (error) {
            std::cerr << "Could not write: " << boost::system::system_error(error).what() << std::endl;
            return;
        }

        if (!_outbox.empty()) {
            // More messages to send
            this->write();
        }
    }

private:
    typedef std::deque<std::string> Outbox;

private:
    boost::asio::io_service& _io_service;
    boost::asio::io_service::strand _strand;
    boost::asio::ip::tcp::socket _socket;
    Outbox _outbox;
};