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

boost::asio::ip::udp:socket can not cancel() the async_handle, nor close().

This is the test program:


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");



with boost 1.67.0, WIN10, vs2017 BOOST_ASIO_DISABLE_IOCP and BOOST_ASIO_CANCELIO defined according to the documentation

Did i fail to get the point?

If i am correct , how to fix this problem ?

1 Answer
1

Asynchronous operations do not complete immediately. Your code looks like you expect them to.

Simplifying your code to:

Live On Coliru

#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();



It makes sense that the handler only run AFTER io.run(); And obviously the socket is only "open" until it got first closed:

io.run()

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


This is exactly expected. So, either you should handle errors:

Live On Coliru

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());
;


Printing instead:

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


Note that perhaps surprisingly, the first send operation still succeeded. Contrary to what I expected this indicates that the send is actually initiated right at the async_send_to call, but the completion is delayed until after io.run() (the socket is still shown to be already closed).

async_send_to

io.run()

And maybe you did not want async operations at all:

Live On Coliru

#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();



Prints

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


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