提升：：ASIO 取消或关闭对async_handle不起作用

boost::asio cancel or close doesn't work on async_handle

本文关键字：async 不起作用 handle ASIO 取消 提升      更新时间：2023-10-16

boost：：asio：：ip：：udp：socket 不能取消 (( async_handle，也不能关闭((。

这是测试程序：

{
boost::asio::io_context io_core;
boost::asio::ip::udp::socket udp_socket1(io_core, udp::v4());
char buff[200];
boost::asio::ip::udp::endpoint endpoint1(boost::asio::ip::address::from_string("127.0.0.1"), 9999);
cout << udp_socket1.is_open() << endl;
udp_socket1.async_send_to(boost::asio::buffer(buff, 200), endpoint1, [&udp_socket1](const boost::system::error_code& ec, size_t wlen) {
cout << udp_socket1.is_open() << endl;
//assert(0);
});
cout << udp_socket1.is_open() << endl;
udp_socket1.close();
udp_socket1.async_send_to(boost::asio::buffer(buff, 200), endpoint1, [&udp_socket1](const boost::system::error_code& ec, size_t wlen) {
cout << udp_socket1.is_open() << endl;
//assert(0);
});
cout << udp_socket1.is_open() << endl;
udp_socket1.close();
io_core.run();
system("pause");
}

根据文档定义 Boost 1.67.0、WIN10、vs2017 BOOST_ASIO_DISABLE_IOCP和BOOST_ASIO_CANCELIO

我没明白重点吗？

如果我是对的，如何解决这个问题？

异步操作不会立即完成。您的代码看起来与您期望的一样。

简化代码以：

住在科里鲁 

#include <boost/asio.hpp>
#include <iostream>
using boost::asio::ip::udp;
int main() {
std::cout << std::boolalpha;
boost::asio::io_context io;
boost::asio::ip::udp::socket s {io, udp::v4()};
boost::asio::ip::udp::endpoint const ep {{}, 9999};
auto trace = [&s](char const* caption) { std::cout << caption << s.is_open() << std::endl; };
auto handler = [=](boost::system::error_code, size_t) { trace("handler: "); };
trace("main #1: ");
char buff[200] = {};
s.async_send_to(boost::asio::buffer(buff), ep, handler);
trace("main #2: ");
s.close();
s.async_send_to(boost::asio::buffer(buff), ep, handler);
trace("main #3: ");
s.close();
io.run();
}

处理程序仅在io.run()之后运行是有道理的;显然，插座在第一次关闭之前只是"打开"的：

main #1: true
main #2: true
main #3: false
handler: false
handler: false

这完全是意料之中的。因此，您应该处理错误：

住在科里鲁

auto trace = [&s](char const* caption) { std::cout << caption << (s.is_open()?"open":"closed") << std::endl; };
auto handler = [=](boost::system::error_code ec, size_t) { 
trace(("handler(" + ec.message() + "): ").c_str()); 
};

改为打印：

main #1: open
main #2: open
main #3: closed
handler(Success): closed
handler(Bad file descriptor): closed

请注意，也许令人惊讶的是，第一个发送操作仍然成功。与我的预期相反，这表明发送实际上是在async_send_to调用时启动的，但完成延迟到io.run()之后(套接字仍然显示为已经关闭(。

也许你根本不想要异步操作：

住在科里鲁

#include <boost/asio.hpp>
#include <iostream>
using boost::asio::ip::udp;
int main() {
std::cout << std::boolalpha;
boost::asio::io_context io;
boost::asio::ip::udp::socket s {io, udp::v4()};
boost::asio::ip::udp::endpoint const ep {{}, 9999};
auto trace = [&s](char const* caption) { std::cout << caption << s.is_open() << std::endl; };
trace("main #1: ");
char buff[200] = {};
try {
/*size_t wlen =*/ s.send_to(boost::asio::buffer(buff), ep);
trace("sent #1: ");
} catch(boost::system::system_error const& e) {
std::cout << "Send #1 failed: " << e.code().message() << std::endl;
}
trace("main #2: ");
s.close();
try {
/*size_t wlen =*/ s.send_to(boost::asio::buffer(buff), ep);
trace("sent #2: ");
} catch(boost::system::system_error const& e) {
std::cout << "Send #2 failed: " << e.code().message() << std::endl;
}
trace("main #3: ");
s.close();
io.run();
}

指纹

main #1: true
sent #1: true
main #2: true
Send #2 failed: Bad file descriptor
main #3: false
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