windows_event_cancel.cpp

/**
 * @author github.com/luncliff (luncliff@gmail.com)
 */
#undef NDEBUG
#include <atomic>
#include <cassert>
#include <iostream>

#include <gsl/gsl>

#include <coroutine/return.h>
#include <coroutine/windows.h>

using namespace std;
using namespace coro;

auto wait_an_event(set_or_cancel& token, atomic_flag& flag) -> frame_t;
auto set_after_sleep(HANDLE ev, uint32_t ms) -> frame_t;

int main(int, char*[]) {
    HANDLE e = CreateEventEx(nullptr, nullptr, //
                             CREATE_EVENT_MANUAL_RESET, EVENT_ALL_ACCESS);
    assert(e != NULL);
    auto on_return_1 = gsl::finally([e]() { CloseHandle(e); });

    ResetEvent(e);
    set_or_cancel evt{e};
    atomic_flag flag = ATOMIC_FLAG_INIT;

    auto frame = wait_an_event(evt, flag);
    auto on_return_2 = gsl::finally([&frame]() { frame.destroy(); });
    // cancel by unregister
    if (auto ec = evt.unregister()) {
        cerr << system_category().message(ec) << endl;
        return __LINE__;
    }

    // give time to windows threads
    SleepEx(300, true);
    return flag.test_and_set() == true ? EXIT_FAILURE : EXIT_SUCCESS;
}

auto wait_an_event(set_or_cancel& evt, atomic_flag& flag) -> frame_t {
    // wait for set or cancel
    // `co_await` will forward `GetLastError` if canceled.
    if (DWORD ec = co_await evt) {
        cerr << system_category().message(ec) << endl;
        co_return;
    }
    flag.test_and_set();
}

auto set_after_sleep(HANDLE ev, uint32_t ms) -> frame_t {
    // move to background thread ...
    co_await continue_on_thread_pool{};
    SleepEx(ms, true);
    // if failed, print error message
    if (SetEvent(ev) == FALSE)
        cerr << system_category().message(GetLastError()) << endl;
}