我正在尝试学习提升asio socket。在boost网页中有一个有趣的例子,它设置了一个监视超时的截止时间,并将async io改为同步时尚。但当我删除截止时间计时器时,程序卡在write_line中的while循环中,我不明白为什么可以设置连接但是套接字写入被卡住了。似乎写作从未完成,处理程序从未调用过,因此“ec”从未改变过。先感谢您!!
#include <boost/asio/connect.hpp>
#include <boost/asio/deadline_timer.hpp>
#include <boost/asio/io_service.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/read_until.hpp>
#include <boost/asio/streambuf.hpp>
#include <boost/system/system_error.hpp>
#include <boost/asio/write.hpp>
#include <cstdlib>
#include <iostream>
#include <string>
#include <boost/bind.hpp>
using boost::asio::deadline_timer;
using boost::asio::ip::tcp;
class client
{
public:
client()
: socket_(io_service_),
deadline_(io_service_)
{
deadline_.expires_from_now(boost::posix_time::seconds(10));
check_deadline(); // without this line which means without the this timer
//async_wait, the code stuck in write_line io_service_.run_one() loop .
}
void connect_handler(const boost::system::error_code& error,boost::system::error_code *er)
{
std::cerr<<"connect handler"<<std::endl;
*er = error;
std::cerr<<error<<std::endl;
}
void connect(const std::string& host, const std::string& service)
{
tcp::resolver::query query(host, service);
tcp::resolver::iterator iter = tcp::resolver(io_service_).resolve(query);
std::cerr<<"connect start"<<std::endl;
boost::system::error_code ec = boost::asio::error::would_block;
boost::asio::async_connect(socket_, iter, bind(&client::connect_handler,this,_1,&ec));
do
{io_service_.run_one();
}while (ec == boost::asio::error::would_block);
std::cerr<<"connect done"<<std::endl; // always works fine!
if (ec || !socket_.is_open())
throw boost::system::system_error(
ec ? ec : boost::asio::error::operation_aborted);
}
void write_handler(const boost::system::error_code& error, std::size_t size,boost::system::error_code* er )
{
std::cerr<<"write handler "<<std::endl;
*er=error;
std::cerr<<error<<std::endl;
}
void write_line(const std::string& line)
{
std::cerr<<"write start"<<std::endl;
std::string data = line + "\n";
boost::system::error_code ec = boost::asio::error::would_block;
boost::asio::async_write(socket_, boost::asio::buffer(data), bind(&client::write_handler,this,_1,_2,&ec));
do
{
io_service_.run_one(); //stuck here without "check_deadline();" in constructor.
}while (ec == boost::asio::error::would_block);
std::cerr<<"write done";
if (ec)
throw boost::system::system_error(ec);
}
private:
void check_deadline()
{
if (deadline_.expires_at() <= deadline_timer::traits_type::now())
{
boost::system::error_code ignored_ec;
socket_.close(ignored_ec);
deadline_.expires_at(boost::posix_time::pos_infin);
throw boost::system::system_error(ignored_ec);
}
deadline_.async_wait(std::bind(&client::check_deadline, this));
}
boost::asio::io_service io_service_;
tcp::socket socket_;
deadline_timer deadline_;
};
int main()
{
try
{
client c,d;
c.connect("216.58.194.164", "80");// google IP.
c.write_line("test");
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
没有注释掉行“check_deadline();”在构造函数中,输出为:
connect start
connect handler
system:0
connect done
write start
write handler
system:0
write done
当行“check_deadline();”在构造函数中注释掉,输出是:
connect start
connect handler
system:0
connect done
write start
永远地卡在那里。
答案 0 :(得分:0)
该特定示例的重点是阻止操作超时。这就是他们使用函数的async_ *风格的原因。
如果您不需要 ,请不要使用async_ *风格:
#include <boost/asio.hpp>
#include <iostream>
#include <string>
using boost::asio::ip::tcp;
class client {
public:
client() : socket_(io_service_) { }
void connect(const std::string &host, const std::string &service) {
tcp::resolver::query query(host, service);
socket_.close();
boost::asio::connect(socket_, tcp::resolver(io_service_).resolve(query));
}
std::string read_line() {
boost::system::error_code ec;
boost::asio::read_until(socket_, input_buffer_, '\n', ec);
if (ec == boost::asio::error::eof)
socket_.close();
else if (ec)
throw boost::system::system_error(ec);
std::string line;
std::getline(std::istream(&input_buffer_), line);
return line;
}
void write_line(const std::string &line) {
std::string data = line + "\n";
boost::asio::write(socket_, boost::asio::buffer(data));
}
private:
boost::asio::io_service io_service_;
tcp::socket socket_;
boost::asio::streambuf input_buffer_;
};
int main(int argc, char *argv[]) {
try {
if (argc != 4) {
std::cerr << "Usage: blocking_tcp <host> <port> <message>\n";
return 1;
}
client c;
c.connect(argv[1], argv[2]);
boost::posix_time::ptime time_sent = boost::posix_time::microsec_clock::universal_time();
c.write_line(argv[3]);
for (;;) {
std::string line = c.read_line();
std::cout << "Received '" << line << "'\n";
if (line == argv[3])
break;
}
boost::posix_time::ptime time_received = boost::posix_time::microsec_clock::universal_time();
std::cout << "Round trip time: ";
std::cout << (time_received - time_sent).total_microseconds();
std::cout << " microseconds\n";
} catch (std::exception &e) {
std::cerr << "Exception: " << e.what() << "\n";
}
}
这简单得多。实际上,如果一次到达的数据包包含多于1行,则过于简单。
不是通过使样品重新复杂化来“修复”样品,而是非常简单:
#include <boost/asio.hpp>
#include <iostream>
#include <string>
using boost::asio::ip::tcp;
int main(int argc, char *argv[]) {
try {
if (argc != 4) {
std::cerr << "Usage: blocking_tcp <host> <port> <message>\n";
return 1;
}
tcp::iostream c(argv[1], argv[2]);
boost::posix_time::ptime time_sent = boost::posix_time::microsec_clock::universal_time();
c << argv[3] << "\n";
std::string line;
while (getline(c, line)) {
std::cout << "Received '" << line << "'\n";
if (line == argv[3])
break;
}
boost::posix_time::ptime time_received = boost::posix_time::microsec_clock::universal_time();
std::cout << "Round trip time: ";
std::cout << (time_received - time_sent).total_microseconds();
std::cout << " microseconds\n";
} catch (std::exception &e) {
std::cerr << "Exception: " << e.what() << "\n";
}
}