Why doesn't boost::asio::ip::udp::socket::receive_from throw interruption exception in Windows?

Question

volatile std::sig_atomic_t running = true;

int main()
{
  boost::asio::thread_pool tpool;
  boost::asio::signal_set signals(tpool, SIGINT, SIGTERM);
  signals.async_wait([](auto && err, int) { if (!err) running = false; });

  while(running)
  {
    std::array<std::uint8_t, 1024> data;
    socket.recieve_from(boost::asio::buffer(data), ....); // (1)
    // calc(data);
  }
  return 0;
}

If my code is blocked in the (1) line in Linux and I try raise the signal, for example, with htop then the line (1) throws exception about the interruption but in Windows it doesn't. The problem in what I don't know how to exit the application.

What needs to do my program works equally in both OSs? Thanks.

Use Windows 10 (msvc 17), Debian 11 (gcc-9), Boost 1.78.

Answer 1

Regardless of the question how you "raise the signal" on Windows there's the basic problem that you're relying on OS specifics to cancel a synchronous operation.

Cancellation is an ASIO feature, but only for asynchronous operations. So, consider:

signals.async_wait([&socket](auto&& err, int) {
    if (!err) {
        socket.cancel();
    }
});

Simplifying without a thread_pool gives e.g.:

Live On Coliru

#define BOOST_ASIO_ENABLE_HANDLER_TRACKING 1
#include <boost/asio.hpp>
namespace asio = boost::asio;
using asio::ip::udp;
using boost::system::error_code;

struct Program {
    Program(asio::any_io_executor executor)
        : signals_{executor, SIGINT, SIGTERM}
        , socket_{executor} //
    {
        signals_.async_wait([this](error_code ec, int) {
            if (!ec) {
                socket_.cancel();
            }
        });

        socket_.open(udp::v4());
        socket_.bind({{}, 4444});
        receive_loop();
    }

  private:
    asio::signal_set signals_;
    udp::socket      socket_;

    std::array<std::uint8_t, 1024> data_;
    udp::endpoint                  ep_;

    void receive_loop() {
        socket_.async_receive_from( //
            asio::buffer(data_), ep_, [this](error_code ec, size_t) {
                if (!ec)
                    receive_loop();
            });
    }
};

int main() {
    asio::io_context ioc;
    Program app(ioc.get_executor());

    using namespace std::chrono_literals;
    ioc.run_for(10s); // for COLIRU
}

Prints (on coliru):

@asio|1663593973.457548|0*1|signal_set@0x7ffe0b639998.async_wait
@asio|1663593973.457687|0*2|socket@0x7ffe0b6399f0.async_receive_from
@asio|1663593973.457700|.2|non_blocking_recvfrom,ec=system:11,bytes_transferred=0
@asio|1663593974.467205|.2|non_blocking_recvfrom,ec=system:0,bytes_transferred=13
@asio|1663593974.467252|>2|ec=system:0,bytes_transferred=13
@asio|1663593974.467265|2*3|socket@0x7ffe0b6399f0.async_receive_from
@asio|1663593974.467279|.3|non_blocking_recvfrom,ec=system:11,bytes_transferred=0
@asio|1663593974.467291|<2|
@asio|1663593975.481800|.3|non_blocking_recvfrom,ec=system:0,bytes_transferred=13
@asio|1663593975.481842|>3|ec=system:0,bytes_transferred=13
@asio|1663593975.481854|3*4|socket@0x7ffe0b6399f0.async_receive_from
@asio|1663593975.481868|.4|non_blocking_recvfrom,ec=system:11,bytes_transferred=0
@asio|1663593975.481878|<3|
@asio|1663593976.494097|.4|non_blocking_recvfrom,ec=system:0,bytes_transferred=13
@asio|1663593976.494138|>4|ec=system:0,bytes_transferred=13
@asio|1663593976.494150|4*5|socket@0x7ffe0b6399f0.async_receive_from
@asio|1663593976.494164|.5|non_blocking_recvfrom,ec=system:11,bytes_transferred=0
@asio|1663593976.494176|<4|
@asio|1663593976.495085|>1|ec=system:0,signal_number=2
@asio|1663593976.495119|1|socket@0x7ffe0b6399f0.cancel
@asio|1663593976.495129|<1|
@asio|1663593976.495151|>5|ec=system:125,bytes_transferred=0
@asio|1663593976.495162|<5|
@asio|1663593976.495184|0|socket@0x7ffe0b6399f0.close
@asio|1663593976.495244|0|signal_set@0x7ffe0b639998.cancel

So that's 3 successful receives, followed by a signal 2 (INT) and cancellation which results in ec=125 (asio::error:operation_aborted) and shutdown.

Multi-threading

There's likely no gain for using multiple threads, but if you do, use a strand to synchronize access to the IO objects:

asio::thread_pool ioc;
Program app(make_strand(ioc));