How to make a timeout at receiving in boost::asio udp::socket? - c++

Question

I create an one-thread application which exchanges with another one via UDP. When the second is disconnecting, my socket::receive_from blocks and I don't know how to solve this problem not changing the entire program into multi-threads or async interactions.
I thought that next may be a solution:
std::chrono::milliseconds timeout{4};
boost::system::error_code err;
data_t buffer(kPackageMaxSize);
std::size_t size = 0;
const auto status = std::async(std::launch::async,
[&]{
size = socket_.receive_from(boost::asio::buffer(buffer), dst_, 0, err);
}
).wait_for(timeout);
switch (status)
{
case std::future_status::timeout: /*...*/ break;
}
But I achieved a new problem: Qt Creator (GDB 11.1) (I don't have ability to try something yet) began to fall when I am debugging. If it runs without, the solution also not always works.

Answer 1

PS. As for "it doesn't work when debugging", debugging (specifically breakpoints) obviously changes timing. Also, keep in mind network operations have varying latency and UDP isn't a guaranteed protocol: messages may not be delivered.
Asio stands for "Asynchronous IO". As you might suspect, this means that asynchronous IO is a built-in feature, it's the entire purpose of the library. See overview/core/async.html: Concurrency Without Threads
It's not necessary to complicate with std::async. In your case I'd suggest using async_receive_from with use_future, as it is closest to the model you opted for:
Live On Coliru
#include <boost/asio.hpp>
#include <iostream>
#include <iomanip>
namespace net = boost::asio;
using net::ip::udp;
using namespace std::chrono_literals;
constexpr auto kPackageMaxSize = 65520;
using data_t = std::vector<char>;
int main() {
net::thread_pool ioc;
udp::socket socket_(ioc, udp::v4());
socket_.bind({{}, 8989});
udp::endpoint ep;
data_t buffer(kPackageMaxSize);
auto fut =
socket_.async_receive_from(net::buffer(buffer), ep, net::use_future);
switch (fut.wait_for(4ms)) {
case std::future_status::ready: {
buffer.resize(fut.get()); // never blocks here
std::cout << "Received " << buffer.size() << " bytes: "
<< std::quoted(
std::string_view(buffer.data(), buffer.size()))
<< "\n";
break;
}
case std::future_status::timeout:
case std::future_status::deferred: {
std::cout << "Timeout\n";
socket_.cancel(); // stop the IO operation
// fut.get() would throw system_error(net::error::operation_aborted)
break;
}
}
ioc.join();
}
The Coliru output:
Received 12 bytes: "Hello World
"
Locally demonstrating both timeout and successful path: