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|
//
// blocking_udp_client.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include <boost/asio/deadline_timer.hpp>
#include <boost/asio/io_service.hpp>
#include <boost/asio/ip/udp.hpp>
#include <cstdlib>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <iostream>
using boost::asio::deadline_timer;
using boost::asio::ip::udp;
//----------------------------------------------------------------------
//
// This class manages socket timeouts by applying the concept of a deadline.
// Each asynchronous operation is given a deadline by which it must complete.
// Deadlines are enforced by an "actor" that persists for the lifetime of the
// client object:
//
// +----------------+
// | |
// | check_deadline |<---+
// | | |
// +----------------+ | async_wait()
// | |
// +---------+
//
// If the actor determines that the deadline has expired, any outstanding
// socket operations are cancelled. The socket operations themselves are
// implemented as transient actors:
//
// +---------------+
// | |
// | receive |
// | |
// +---------------+
// |
// async_- | +----------------+
// receive() | | |
// +--->| handle_receive |
// | |
// +----------------+
//
// The client object runs the io_service to block thread execution until the
// actor completes.
//
class client
{
public:
client(const udp::endpoint& listen_endpoint)
: socket_(io_service_, listen_endpoint),
deadline_(io_service_)
{
// No deadline is required until the first socket operation is started. We
// set the deadline to positive infinity so that the actor takes no action
// until a specific deadline is set.
deadline_.expires_at(boost::posix_time::pos_infin);
// Start the persistent actor that checks for deadline expiry.
check_deadline();
}
std::size_t receive(const boost::asio::mutable_buffer& buffer,
boost::posix_time::time_duration timeout, boost::system::error_code& ec)
{
// Set a deadline for the asynchronous operation.
deadline_.expires_from_now(timeout);
// Set up the variables that receive the result of the asynchronous
// operation. The error code is set to would_block to signal that the
// operation is incomplete. Asio guarantees that its asynchronous
// operations will never fail with would_block, so any other value in
// ec indicates completion.
ec = boost::asio::error::would_block;
std::size_t length = 0;
// Start the asynchronous operation itself. The handle_receive function
// used as a callback will update the ec and length variables.
socket_.async_receive(boost::asio::buffer(buffer),
boost::bind(&client::handle_receive, _1, _2, &ec, &length));
// Block until the asynchronous operation has completed.
do io_service_.run_one(); while (ec == boost::asio::error::would_block);
return length;
}
private:
void check_deadline()
{
// 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. The outstanding asynchronous operation needs
// to be cancelled so that the blocked receive() function will return.
//
// Please note that cancel() has portability issues on some versions of
// Microsoft Windows, and it may be necessary to use close() instead.
// Consult the documentation for cancel() for further information.
socket_.cancel();
// There is no longer an active deadline. The expiry is set to positive
// infinity so that the actor takes no action until a new deadline is set.
deadline_.expires_at(boost::posix_time::pos_infin);
}
// Put the actor back to sleep.
deadline_.async_wait(boost::bind(&client::check_deadline, this));
}
static void handle_receive(
const boost::system::error_code& ec, std::size_t length,
boost::system::error_code* out_ec, std::size_t* out_length)
{
*out_ec = ec;
*out_length = length;
}
private:
boost::asio::io_service io_service_;
udp::socket socket_;
deadline_timer deadline_;
};
//----------------------------------------------------------------------
int main(int argc, char* argv[])
{
try
{
using namespace std; // For atoi.
if (argc != 3)
{
std::cerr << "Usage: blocking_udp_timeout <listen_addr> <listen_port>\n";
return 1;
}
udp::endpoint listen_endpoint(
boost::asio::ip::address::from_string(argv[1]),
std::atoi(argv[2]));
client c(listen_endpoint);
for (;;)
{
char data[1024];
boost::system::error_code ec;
std::size_t n = c.receive(boost::asio::buffer(data),
boost::posix_time::seconds(10), ec);
if (ec)
{
std::cout << "Receive error: " << ec.message() << "\n";
}
else
{
std::cout << "Received: ";
std::cout.write(data, n);
std::cout << "\n";
}
}
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
|
