boost-asio 超时的服务器示例有 3 个命令行参数。我需要知道第二个和第三个是什么以及如何测试服务器（在哪里Usage: server <listen_port> <bcast_address> <bcast_port>）。它说它们是广播端口和地址，但如果我在一台机器上作为本地主机（例如 127.0.0.1）测试它，那么会发生什么？
这是代码
#include <algorithm>
#include <cstdlib>
#include <deque>
#include <iostream>
#include <set>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio/deadline_timer.hpp>
#include <boost/asio/io_service.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/ip/udp.hpp>
#include <boost/asio/read_until.hpp>
#include <boost/asio/streambuf.hpp>
#include <boost/asio/write.hpp>
using boost::asio::deadline_timer;
using boost::asio::ip::tcp;
using boost::asio::ip::udp;
//----------------------------------------------------------------------
class subscriber
{
public:
virtual ~subscriber() {}
virtual void deliver(const std::string& msg) = 0;
};
typedef boost::shared_ptr<subscriber> subscriber_ptr;
//----------------------------------------------------------------------
class channel
{
public:
void join(subscriber_ptr subscriber)
{
subscribers_.insert(subscriber);
}
void leave(subscriber_ptr subscriber)
{
subscribers_.erase(subscriber);
}
void deliver(const std::string& msg)
{
std::for_each(subscribers_.begin(), subscribers_.end(),
boost::bind(&subscriber::deliver, _1, boost::ref(msg)));
}
private:
std::set<subscriber_ptr> subscribers_;
};
//----------------------------------------------------------------------
//
// This class manages socket timeouts by applying the concept of a deadline.
// Some asynchronous operations are given deadlines by which they must complete.
// Deadlines are enforced by two "actors" that persist for the lifetime of the
// session object, one for input and one for output:
//
// +----------------+ +----------------+
// | | | |
// | check_deadline |<---+ | check_deadline |<---+
// | | | async_wait() | | | async_wait()
// +----------------+ | on input +----------------+ | on output
// | | deadline | | deadline
// +---------+ +---------+
//
// If either deadline actor determines that the corresponding deadline has
// expired, the socket is closed and any outstanding operations are cancelled.
//
// The input actor reads messages from the socket, where messages are delimited
// by the newline character:
//
// +------------+
// | |
// | start_read |<---+
// | | |
// +------------+ |
// | |
// async_- | +-------------+
// read_- | | |
// until() +--->| handle_read |
// | |
// +-------------+
//
// The deadline for receiving a complete message is 30 seconds. If a non-empty
// message is received, it is delivered to all subscribers. If a heartbeat (a
// message that consists of a single newline character) is received, a heartbeat
// is enqueued for the client, provided there are no other messages waiting to
// be sent.
//
// The output actor is responsible for sending messages to the client:
//
// +--------------+
// | |<---------------------+
// | await_output | |
// | |<---+ |
// +--------------+ | |
// | | | async_wait() |
// | +--------+ |
// V |
// +-------------+ +--------------+
// | | async_write() | |
// | start_write |-------------->| handle_write |
// | | | |
// +-------------+ +--------------+
//
// The output actor first waits for an output message to be enqueued. It does
// this by using a deadline_timer as an asynchronous condition variable. The
// deadline_timer will be signalled whenever the output queue is non-empty.
//
// Once a message is available, it is sent to the client. The deadline for
// sending a complete message is 30 seconds. After the message is successfully
// sent, the output actor again waits for the output queue to become non-empty.
//
class tcp_session
: public subscriber,
public boost::enable_shared_from_this<tcp_session>
{
public:
tcp_session(boost::asio::io_service& io_service, channel& ch)
: channel_(ch),
socket_(io_service),
input_deadline_(io_service),
non_empty_output_queue_(io_service),
output_deadline_(io_service)
{
input_deadline_.expires_at(boost::posix_time::pos_infin);
output_deadline_.expires_at(boost::posix_time::pos_infin);
// The non_empty_output_queue_ deadline_timer is set to pos_infin whenever
// the output queue is empty. This ensures that the output actor stays
// asleep until a message is put into the queue.
non_empty_output_queue_.expires_at(boost::posix_time::pos_infin);
}
tcp::socket& socket()
{
return socket_;
}
// Called by the server object to initiate the four actors.
void start()
{
channel_.join(shared_from_this());
start_read();
input_deadline_.async_wait(
boost::bind(&tcp_session::check_deadline,
shared_from_this(), &input_deadline_));
await_output();
output_deadline_.async_wait(
boost::bind(&tcp_session::check_deadline,
shared_from_this(), &output_deadline_));
}
private:
void stop()
{
channel_.leave(shared_from_this());
boost::system::error_code ignored_ec;
socket_.close(ignored_ec);
input_deadline_.cancel();
non_empty_output_queue_.cancel();
output_deadline_.cancel();
}
bool stopped() const
{
return !socket_.is_open();
}
void deliver(const std::string& msg)
{
output_queue_.push_back(msg + "\n");
// Signal that the output queue contains messages. Modifying the expiry
// will wake the output actor, if it is waiting on the timer.
non_empty_output_queue_.expires_at(boost::posix_time::neg_infin);
}
void start_read()
{
// Set a deadline for the read operation.
input_deadline_.expires_from_now(boost::posix_time::seconds(30));
// Start an asynchronous operation to read a newline-delimited message.
boost::asio::async_read_until(socket_, input_buffer_, '\n',
boost::bind(&tcp_session::handle_read, shared_from_this(), _1));
}
void handle_read(const boost::system::error_code& ec)
{
if (stopped())
return;
if (!ec)
{
// Extract the newline-delimited message from the buffer.
std::string msg;
std::istream is(&input_buffer_);
std::getline(is, msg);
if (!msg.empty())
{
channel_.deliver(msg);
}
else
{
// We received a heartbeat message from the client. If there's nothing
// else being sent or ready to be sent, send a heartbeat right back.
if (output_queue_.empty())
{
output_queue_.push_back("\n");
// Signal that the output queue contains messages. Modifying the
// expiry will wake the output actor, if it is waiting on the timer.
non_empty_output_queue_.expires_at(boost::posix_time::neg_infin);
}
}
start_read();
}
else
{
stop();
}
}
void await_output()
{
if (stopped())
return;
if (output_queue_.empty())
{
// There are no messages that are ready to be sent. The actor goes to
// sleep by waiting on the non_empty_output_queue_ timer. When a new
// message is added, the timer will be modified and the actor will wake.
non_empty_output_queue_.expires_at(boost::posix_time::pos_infin);
non_empty_output_queue_.async_wait(
boost::bind(&tcp_session::await_output, shared_from_this()));
}
else
{
start_write();
}
}
void start_write()
{
// Set a deadline for the write operation.
output_deadline_.expires_from_now(boost::posix_time::seconds(30));
// Start an asynchronous operation to send a message.
boost::asio::async_write(socket_,
boost::asio::buffer(output_queue_.front()),
boost::bind(&tcp_session::handle_write, shared_from_this(), _1));
}
void handle_write(const boost::system::error_code& ec)
{
if (stopped())
return;
if (!ec)
{
output_queue_.pop_front();
await_output();
}
else
{
stop();
}
}
void check_deadline(deadline_timer* deadline)
{
if (stopped())
return;
// Check whether the deadline has passed. We compare the deadline against
// the current time since a new asynchronous operation may have moved the
// deadline before this actor had a chance to run.
if (deadline->expires_at() <= deadline_timer::traits_type::now())
{
// The deadline has passed. Stop the session. The other actors will
// terminate as soon as possible.
stop();
}
else
{
// Put the actor back to sleep.
deadline->async_wait(
boost::bind(&tcp_session::check_deadline,
shared_from_this(), deadline));
}
}
channel& channel_;
tcp::socket socket_;
boost::asio::streambuf input_buffer_;
deadline_timer input_deadline_;
std::deque<std::string> output_queue_;
deadline_timer non_empty_output_queue_;
deadline_timer output_deadline_;
};
typedef boost::shared_ptr<tcp_session> tcp_session_ptr;
//----------------------------------------------------------------------
class udp_broadcaster
: public subscriber
{
public:
udp_broadcaster(boost::asio::io_service& io_service,
const udp::endpoint& broadcast_endpoint)
: socket_(io_service)
{
socket_.connect(broadcast_endpoint);
}
private:
void deliver(const std::string& msg)
{
boost::system::error_code ignored_ec;
socket_.send(boost::asio::buffer(msg), 0, ignored_ec);
}
udp::socket socket_;
};
//----------------------------------------------------------------------
class server
{
public:
server(boost::asio::io_service& io_service,
const tcp::endpoint& listen_endpoint,
const udp::endpoint& broadcast_endpoint)
: io_service_(io_service),
acceptor_(io_service, listen_endpoint)
{
subscriber_ptr bc(new udp_broadcaster(io_service_, broadcast_endpoint));
channel_.join(bc);
start_accept();
}
void start_accept()
{
tcp_session_ptr new_session(new tcp_session(io_service_, channel_));
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session, _1));
}
void handle_accept(tcp_session_ptr session,
const boost::system::error_code& ec)
{
if (!ec)
{
session->start();
}
start_accept();
}
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
channel channel_;
};
//----------------------------------------------------------------------
int main(int argc, char* argv[])
{
try
{
using namespace std; // For atoi.
if (argc != 4)
{
std::cerr << "Usage: server <listen_port> <bcast_address> <bcast_port>\n";
return 1;
}
boost::asio::io_service io_service;
tcp::endpoint listen_endpoint(tcp::v4(), atoi(argv[1]));
udp::endpoint broadcast_endpoint(
boost::asio::ip::address::from_string(argv[2]), atoi(argv[3]));
server s(io_service, listen_endpoint, broadcast_endpoint);
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}