我是 boost::asio 的新手,并且遇到了第一个麻烦。我创建了一个简单的主机解析器(请参阅下面的完整代码)。
问题 1. 如果 Internet 连接断开,我的主机解析器在第一次进入截止时间定时器后停止解析。我的假设是,必须随时解决“localhost”。但是“localhost”在解析 google.us 期间超时后未解析(例如,我们拔掉了以太网插孔)。在解析不存在的 TLD(例如,用 google.usd 代替 google.us)时的相同行为。
问题 2. 如果 Internet 连接丢失,析构函数 io_service 会运行很长时间(通常为 5 秒)。
怎么了?
我用VS2012,升压1.54
文件 hostresolver.h
pragma once
#include <set>
#include <boost/system/error_code.hpp>
#include <boost/asio.hpp>
#include <boost/asio/ip/basic_resolver.hpp>
#include <boost/asio/ip/basic_resolver_iterator.hpp>
typedef std::set<unsigned long> hostresolver_result_container;
class hostresolver
{
public:
hostresolver(boost::asio::io_service* io_service);
~hostresolver(void);
boost::asio::io_service* ios_ptr;
boost::asio::ip::tcp::resolver resolver_;
boost::asio::deadline_timer timer_;
volatile bool is_completed;
bool is_timeout;
std::string hostname;
hostresolver_result_container result;
void on_timeout(const boost::system::error_code &err);
void start_resolve(const char* hostname, int timeout_seconds);
void finish_resolve(const boost::system::error_code& err, boost::asio::ip::tcp::resolver::iterator endpoint_iterator);
private:
void stop();
};
文件 hostresolver.cpp
#include "stdafx.h"
#include "hostresolver.h"
#include <boost/bind.hpp>
hostresolver::hostresolver(boost::asio::io_service* io_service) :
resolver_(*io_service), timer_(*io_service), is_completed(false), is_timeout(false)
{
ios_ptr = io_service;
}
hostresolver::~hostresolver(void)
{
}
void hostresolver::start_resolve(const char* hostname, int timeout_second)
{
this->hostname.assign(hostname);
timer_.expires_from_now(boost::posix_time::seconds(timeout_second));
timer_.async_wait(boost::bind(&hostresolver::on_timeout, this, _1));
boost::asio::ip::tcp::resolver::query query(hostname, "http");
resolver_.async_resolve(query,
boost::bind(&hostresolver::finish_resolve, this,
boost::asio::placeholders::error,
boost::asio::placeholders::iterator));
do
{
ios_ptr->run_one();
}
while (!is_completed);
}
void hostresolver::stop()
{
resolver_.cancel();
timer_.cancel();
is_completed = true;
}
void hostresolver::on_timeout(const boost::system::error_code &err)
{
if ((!err) && (err != boost::asio::error::operation_aborted))
{
is_timeout = true;
stop();
}
}
void hostresolver::finish_resolve(const boost::system::error_code& err, boost::asio::ip::tcp::resolver::iterator endpoint_iterator)
{
if (!err)
{
while (endpoint_iterator != boost::asio::ip::tcp::resolver::iterator())
{
boost::asio::ip::tcp::endpoint endpoint = *endpoint_iterator;
if (endpoint.address().is_v4())
{
result.insert(endpoint.address().to_v4().to_ulong());
}
endpoint_iterator++;
}
}
stop();
}
文件 main.cpp
#include "stdafx.h"
#include "hostresolver.h"
int _tmain(int argc, _TCHAR* argv[])
{
boost::asio::io_service ios;
for (int i = 0; i < 2; i++)
{
std::cout << "iteration: " << i << std::endl;
{
hostresolver hres(&ios);
hres.start_resolve("localhost", 1);
if (hres.result.size() == 0)
std::cout << "failed" << std::endl;
}
{
hostresolver hres(&ios);
hres.start_resolve("google.usd", 1);
}
}
return 0;
}