我正在移植一个将Boost :: Asio用于嵌入式系统的应用程序。
我已经使用其BSP交叉编译了用于电路板的1.57.0二进制文件。为了测试库的工作原理，我运行了两个分别使用同步和异步写入的http服务器示例。
Sync版本运行良好;而异步的人在写作时失败了。它返回错误“取消操作”。
任何人都可以指出我应该寻找的地方吗？感谢。
/*
* Boost::Asio async example
*/
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/smart_ptr.hpp>
using namespace boost::asio;
using boost::system::error_code;
using ip::tcp;
struct CHelloWorld_Service
{
CHelloWorld_Service(io_service &iosev)
:m_iosev(iosev),m_acceptor(iosev, tcp::endpoint(tcp::v4(), 1000))
{}
void start()
{
boost::shared_ptr<tcp::socket> psocket(new tcp::socket(m_iosev));
m_acceptor.async_accept(*psocket,
boost::bind(&CHelloWorld_Service::accept_handler, this, psocket, _1));
}
void accept_handler(boost::shared_ptr<tcp::socket> psocket, error_code ec)
{
if(ec) return;
start();
std::cout << psocket->remote_endpoint().address() << std::endl;
boost::shared_ptr<std::string> pstr(new std::string("hello async world!"));
psocket->async_write_some(buffer(*pstr),
boost::bind(&CHelloWorld_Service::write_handler, this, pstr, _1, _2));
}
void write_handler(boost::shared_ptr<std::string> pstr, error_code ec,
size_t bytes_transferred)
{
if(ec)
std::cout<< "Failed to send! " << boost::system::system_error(ec).what() << std::endl;
else
std::cout<< *pstr << " has been sent" << std::endl;
}
private:
io_service &m_iosev;
ip::tcp::acceptor m_acceptor;
};
int main(int argc, char* argv[])
{
io_service iosev;
CHelloWorld_Service sev(iosev);
sev.start();
iosev.run();
return 0;
}
答案 0 :(得分：2)
在async_write_some电话中，您忘记保留对套接字实例的引用。
这会导致socket对象被破坏，并且作为析构函数的一部分，所有挂起的异步操作都将被取消。这说明您收到ec operation_aborted。
通过将socket指针添加到绑定参数来修复它，或者将enable_shared_from_this惯用法与CSession类型一起使用。
shared_pointer魔法：这里是最简单的＆＃34;编辑：
void write_handler(
boost::shared_ptr<std::string> pstr,
boost::shared_ptr<tcp::socket> /*keepalive!*/,
error_code ec, size_t bytes_transferred)
{
if(ec)
std::cout<< "Failed to send! " << boost::system::system_error(ec).what() << "\n";
else
std::cout<< *pstr << " has been sent (" << bytes_transferred << " bytes transferred)\n";
}
应该绑定如下：
psocket->async_write_some(ba::buffer(*pstr),
boost::bind(&CService::write_handler, this, pstr, psocket,
ba::placeholders::error, ba::placeholders::bytes_transferred));
<强> Live On Coliru
几种风格改进
using namespace asio占位符（不是_1，_2）打印：
g++ -std=c++11 -O2 -Wall -pedantic main.cpp -pthread -lboost_system -lboost_filesystem && ./a.out& while sleep .1; do nc 127.0.0.1 6767; done
127.0.0.1
hello async world!hello async world! has been sent (18 bytes transferred)
127.0.0.1
hello async world!hello async world! has been sent (18 bytes transferred)
127.0.0.1
hello async world!hello async world! has been sent (18 bytes transferred)
...
CSession（enable_shared_from_this）这是另一个成语，它避免拼写出所有的共享指针。
不要将spearate共享指针保存到套接字和缓冲区，而是创建一个包含两者的类：
struct CSession : boost::enable_shared_from_this<CSession> {
CSession(ba::io_service &iosev)
:m_iosev(iosev), m_sock(m_iosev)
{}
void do_response();
private:
void write_handler(error_code ec, size_t bytes_transferred);
ba::io_service &m_iosev;
tcp::socket m_sock;
std::string response;
};
现在绑定看起来像：
boost::bind(&CSession::write_handler,
shared_from_this(), /* keep-alive! */
ba::placeholders::error, ba::placeholders::bytes_transferred)
更简单。会话管理是CService的责任，与以前一样：
void start()
{
auto session = boost::make_shared<CSession>(m_iosev);
m_acceptor.async_accept(session->m_sock,
boost::bind(&CService::accept_handler, this, session, ba::placeholders::error));
}
void accept_handler(boost::shared_ptr<CSession> session, error_code ec) {
if(ec) {
std::cerr << "Accept failed: " << ec.message() << "\n";
} else {
session->do_response();
start();
}
}
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/make_shared.hpp>
#include <boost/enable_shared_from_this.hpp>
namespace ba = boost::asio;
using boost::system::error_code;
using ba::ip::tcp;
namespace HelloWorld {
struct CSession : boost::enable_shared_from_this<CSession> {
CSession(ba::io_service &iosev)
:m_iosev(iosev), m_sock(m_iosev)
{}
void do_response() {
response = "hello async world!\n";
std::cout << m_sock.remote_endpoint().address() << std::endl;
m_sock.async_write_some(ba::buffer(response),
boost::bind(&CSession::write_handler,
shared_from_this(), /* keep-alive! */
ba::placeholders::error, ba::placeholders::bytes_transferred));
}
private:
void write_handler(error_code ec, size_t bytes_transferred)
{
if(ec)
std::cout<< "Failed to send! " << boost::system::system_error(ec).what() << "\n";
else
std::cout<< response << " has been sent (" << bytes_transferred << " bytes transferred)\n";
}
ba::io_service &m_iosev;
friend class CService;
tcp::socket m_sock;
std::string response;
};
struct CService
{
CService(ba::io_service &iosev)
:m_iosev(iosev),m_acceptor(iosev, tcp::endpoint(tcp::v4(), 6767))
{}
void start() {
auto session = boost::make_shared<CSession>(m_iosev);
m_acceptor.async_accept(session->m_sock,
boost::bind(&CService::accept_handler, this, session, ba::placeholders::error));
}
void accept_handler(boost::shared_ptr<CSession> session, error_code ec) {
if(ec) {
std::cerr << "Accept failed: " << ec.message() << "\n";
} else {
session->do_response();
start();
}
}
private:
ba::io_service &m_iosev;
tcp::acceptor m_acceptor;
};
}
int main() {
ba::io_service iosev;
using namespace HelloWorld;
CService sev(iosev);
sev.start();
iosev.run();
}
输出相似。