提升asio ssl_socket shutdown / close导致SIGSEGV

Question

我在server3上添加了ssl（asio示例）。在极少数情况下，当某些客户端握手失败并且计时器同时到期时，会发生SIGSEGV。

/ var / log / messages中的

消息：

Aborted at 1517935343 (unix time) try "date -d @1517935343" if you are using GNU date <br>
PC: @           0x41ff1b (unknown)  <br>
SIGSEGV (@0x90) received by PID 32728 (TID 0x7f4b9fa79700) from PID 144; stack trace: <br>
0x30fbe0f7e0 (unknown) <br>
0x41ff1b (unknown) <br>
0x419b6a (unknown) <br>
0x41a6a7 (unknown) <br>
0x4229e2 (unknown) <br>
0x4239f2 (unknown) <br>
0x449f59 (unknown) <br>
0x44ca0f (unknown) <br>
0x44d488 (unknown) <br>
0x47defb (unknown) <br>
0x30fbe07aa1 (unknown) <br>
0x3f796e893d (unknown) <br>
0x0 (unknown) <br>
A child(32728) terminated, restart it <br>

connection_s.cpp

void connection_s::start()
{
    //Start timer for monitoring this connectoin's timeout.
    timer_.expires_from_now(boost::posix_time::seconds(20));
    timer_.async_wait(boost::bind(&connection_s::handle_timeout, shared_from_this(), _1));
        socket_.async_handshake(boost::asio::ssl::stream_base::server,
        boost::bind(&connection_s::handle_handshake, shared_from_this(),
          boost::asio::placeholders::error));
}

void connection_s::handle_handshake(const boost::system::error_code& e)
{
    if (!e)
    {
        socket_.async_read_some(boost::asio::buffer(buffer_),
            strand_.wrap(boost::bind(&connection_s::handle_read, shared_from_this(),
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred)));
    } else {
        //eof means that peer has cleanly closed the connection, so we need not to 
        //explicitly stop(shutdown) the connectoin.
        LOG(ERROR) << "Handshake error:" << e.message();
        timer_.cancel();
        stop();
    }
}

void connection_s::stop()
{    
            boost::system::error_code ignored_ec;
socket_.lowest_layer().shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
        if (ignored_ec) {
            LOG(ERROR) << "socket_.lowest_layer().shutdown error message : " << ignored_ec.message() << std::endl;
            return;
        }

        socket_.lowest_layer().close(ignored_ec);
}


void connection_s::handle_timeout(const boost::system::error_code& e)
{
    if (!e)
    {
        boost::system::error_code ec;
        //boost::asio::ip::tcp::endpoint ep = socket().remote_endpoint(ec);
        boost::asio::ip::tcp::endpoint ep = socket().lowest_layer().remote_endpoint(ec);
        if (!ec)
        {
            LOG(WARNING) << "connection_s timeout:" << ep;
        }
        else
        {
            LOG(WARNING) << "connection_s timeout(unknow peer):" << ec.message();
        }
        stop();
    }
}  

我使用了connection_ptr管理connection_s的对象，是什么导致SIGSEGV？
谢谢。