thread_pool_async_io.cpp

void CALLBACK OverlappedCompletionRoutine(PTP_CALLBACK_INSTANCE instance,
                                          PVOID context,
                                          PVOID overlapped,
                                          ULONG io_result,
                                          ULONG_PTR bytes_transferred,
                                          PTP_IO io)
{
    auto ov = static_cast<OVERLAPPED*>(overlapped);
    std::cout << "read " << bytes_transferred << std::endl;
    std::cout << static_cast<char*>(context);
}

int main()
{
    HANDLE file = CreateFile(L"messed.txt",
                             GENERIC_READ,
                             FILE_SHARE_READ,
                             nullptr,
                             OPEN_EXISTING,
                             FILE_FLAG_OVERLAPPED, 
                             nullptr);
    if (file == INVALID_HANDLE_VALUE) {
        std::cerr << "failed to open file messed.txt" << std::endl;
        return EXIT_FAILURE;
    }
    ON_SCOPE_EXIT([&]{ CloseHandle(file); });
    char buf[MAX_PATH] = {0};
    PTP_IO async_io = CreateThreadpoolIo(file, OverlappedCompletionRoutine,
                                         buf, nullptr);
    ON_SCOPE_EXIT([&]{ CloseThreadpoolIo(async_io); });
    StartThreadpoolIo(async_io);
    std::cout << "bind completed" << std::endl;
    OVERLAPPED overlapped = {0};
    ReadFile(file, buf, 20, nullptr, &overlapped);

    _getch();
    return 0;
}