问题描述
我正在尝试从Boost asio示例扩展async_write的相同超时功能： async_tcp_client。
以下是我的代码：
#include <boost/asio/buffer.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/read_until.hpp>
#include <boost/asio/steady_timer.hpp>
#include <boost/asio/write.hpp>
#include <functional>
#include <iostream>
#include <string>
using boost::asio::steady_timer;
using boost::asio::ip::tcp;
using std::placeholders::_1;
using std::placeholders::_2;
class client
{
public:
client(boost::asio::io_context& io_context)
: socket_(io_context),deadline_(io_context),heartbeat_timer_(io_context)
{
}
// Called by the user of the client class to initiate the connection process.
// The endpoints will have been obtained using a tcp::resolver.
void start(tcp::resolver::results_type endpoints)
{
// Start the connect actor.
endpoints_ = endpoints;
start_connect(endpoints_.begin());
// Start the deadline actor. You will note that we're not setting any
// particular deadline here. Instead,the connect and input actors will
// update the deadline prior to each asynchronous operation.
deadline_.async_wait(std::bind(&client::check_deadline,this));
}
// This function terminates all the actors to shut down the connection. It
// may be called by the user of the client class,or by the class itself in
// response to graceful termination or an unrecoverable error.
void stop()
{
stopped_ = true;
boost::system::error_code ignored_error;
socket_.close(ignored_error);
deadline_.cancel();
heartbeat_timer_.cancel();
}
private:
void start_connect(tcp::resolver::results_type::iterator endpoint_iter)
{
if (endpoint_iter != endpoints_.end())
{
std::cout << "Trying " << endpoint_iter->endpoint() << "...\n";
// Set a deadline for the connect operation.
deadline_.expires_after(std::chrono::seconds(60));
// Start the asynchronous connect operation.
socket_.async_connect(endpoint_iter->endpoint(),std::bind(&client::handle_connect,this,_1,endpoint_iter));
}
else
{
// There are no more endpoints to try. Shut down the client.
stop();
}
}
void handle_connect(const boost::system::error_code& error,tcp::resolver::results_type::iterator endpoint_iter)
{
if (stopped_)
return;
// The async_connect() function automatically opens the socket at the start
// of the asynchronous operation. If the socket is closed at this time then
// the timeout handler must have run first.
if (!socket_.is_open())
{
std::cout << "Connect timed out\n";
// Try the next available endpoint.
start_connect(++endpoint_iter);
}
// Check if the connect operation Failed before the deadline expired.
else if (error)
{
std::cout << "Connect error: " << error.message() << "\n";
// We need to close the socket used in the prevIoUs connection attempt
// before starting a new one.
socket_.close();
// Try the next available endpoint.
start_connect(++endpoint_iter);
}
// Otherwise we have successfully established a connection.
else
{
std::cout << "Connected to " << endpoint_iter->endpoint() << "\n";
// Start the input actor.
start_read();
// Start the heartbeat actor.
start_write();
}
}
void start_read()
{
// Set a deadline for the read operation.
//deadline_.expires_after(std::chrono::seconds(30));
// Start an asynchronous operation to read a newline-delimited message.
boost::asio::async_read_until(socket_,boost::asio::dynamic_buffer(input_buffer_),'\n',std::bind(&client::handle_read,_2));
}
void handle_read(const boost::system::error_code& error,std::size_t n)
{
if (stopped_)
return;
if (!error)
{
// Extract the newline-delimited message from the buffer.
std::string line(input_buffer_.substr(0,n - 1));
input_buffer_.erase(0,n);
// Empty messages are heartbeats and so ignored.
if (!line.empty())
{
std::cout << "Received: " << line << "\n";
}
start_read();
}
else
{
std::cout << "Error on receive: " << error.message() << "\n";
stop();
}
}
void start_write()
{
if (stopped_)
return;
// Set a deadline for the write operation.
deadline_.expires_after(std::chrono::seconds(5));
// Start an asynchronous operation to send a heartbeat message.
boost::asio::async_write(socket_,boost::asio::buffer("ping\n",5),std::bind(&client::handle_write,_1));
}
void handle_write(const boost::system::error_code& error)
{
if (stopped_)
return;
if (!error)
{
// Wait 10 seconds before sending the next heartbeat.
heartbeat_timer_.expires_after(std::chrono::seconds(1));
heartbeat_timer_.async_wait(std::bind(&client::start_write,this));
}
else
{
std::cout << "Error on heartbeat: " << error.message() << "\n";
stop();
}
}
void check_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_.expiry() <= steady_timer::clock_type::Now())
{
// The deadline has passed. The socket is closed so that any outstanding
// asynchronous operations are cancelled.
socket_.close();
// There is no longer an active deadline. The expiry is set to the
// maximum time point so that the actor takes no action until a new
// deadline is set.
deadline_.expires_at(steady_timer::time_point::max());
}
// Put the actor back to sleep.
deadline_.async_wait(std::bind(&client::check_deadline,this));
}
private:
bool stopped_ = false;
tcp::resolver::results_type endpoints_;
tcp::socket socket_;
std::string input_buffer_;
steady_timer deadline_;
steady_timer heartbeat_timer_;
};
int main(int argc,char* argv[])
{
try
{
if (argc != 3)
{
std::cerr << "Usage: client <host> <port>\n";
return 1;
}
boost::asio::io_context io_context;
tcp::resolver r(io_context);
client c(io_context);
c.start(r.resolve(argv[1],argv[2]));
io_context.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
我评论async_read的超时功能，并将其放入async_write。但是，async_write函数的超时无效。如果拔出运行服务器的计算机的电缆，则async_write似乎总是会成功，并且不会发生错误。
所以我想知道我是错过了还是做错了什么。希望熟悉此事的人可以帮助我。
解决方法
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