Win32 anonymous pipe broken after first read

Question

I'm creating a process and reading it's stdout and err via the win32 api. Problem is that after the first successfull read with ReadFile(), I'm always getting the broken pipe error (109) for the next one for the data left in the pipe. (so I only read the content as big as the buffer in my first call) I'm suspecting that it's maybe because I'm reading the pipe synchronlysly but after the child terminated?

void read_pipes(std::string &output, HANDLE read_pipe) {
        assert(read_pipe != nullptr && read_pipe != INVALID_HANDLE_VALUE);
        char buffer[4096];
        DWORD bytes_left_to_read, err_code; int i = 0;
        do {
            memset(&buffer, 0, 4096);
            err_code = 0;
            if (!ReadFile(read_pipe, buffer, 4096 - 1, &bytes_left_to_read, NULL)) {
                err_code = GetLastError();
            }
            assert(err_code != ERROR_IO_PENDING);
            if (err_code != 0 && err_code != ERROR_MORE_DATA) {
                char sys_err_msg[128];
                sys_err_msg[128 - 1] = '\0';
                FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, 0, err_code, MAKELANGID(0x09, 0x01), sys_err_msg, 127, nullptr);
                std::cerr << "Failed to read failed mmdb_importer log, because " << sys_err_msg << ";" << err_code
                        << std::endl;
                break;
            }
            output.append(buffer);
        } while (true);

And part of the code which calls the read (full under http://pastebin.com/vakLULyf )

if (WaitForSingleObject(mddb_importer_info.hProcess, 60000) == WAIT_TIMEOUT) {
        //Kill the importer, probably hangs
        TerminateProcess(mddb_importer_info.hProcess, EXIT_FAILURE);
    }
    GetExitCodeProcess(mddb_importer_info.hProcess, &mddb_importer_return);
    //assert (mddb_importer_return != STILL_ACTIVE);

    switch (mddb_importer_return) {
        case EXIT_SUCCESS:
            file_to_upload.uploaded = true;
            break;
        default:
            assert(file_to_upload.uploaded == false);
        {
            read_pipes(std::ref(file_to_upload.log), mddb_importer_stderr_r);
            std::clog << "MDDB_Importer failed with err: : " << file_to_upload.log << std::endl;
            read_pipes(std::ref(file_to_upload.log), mddb_importer_stdout_r);
            std::clog << "And total size of log " << file_to_upload.log.length() << std::endl;
        }
            break;
    }

Answer 1

Yeah looks like I got the ordering wrong, but since I don't want to wait forever on a maybe hanging process, I'm reading in the pipes now by threads I start my read_pipes functions before the waiting with timeout, with std::async. Snipett as example:

    if (!CloseHandle(mddb_importer_stderr_w)) throw std::runtime_error("Can not create mddb_importer pipes");


auto err = std::async(std::launch::async, read_pipes, mddb_importer_stderr_r);
auto out = std::async(std::launch::async, read_pipes, mddb_importer_stdout_r);

if (WaitForSingleObject(mddb_importer_info.hProcess, 60000) == WAIT_TIMEOUT) {
    //Kill the importer, probably hangs
    TerminateProcess(mddb_importer_info.hProcess, EXIT_FAILURE);
}
GetExitCodeProcess(mddb_importer_info.hProcess, &mddb_importer_return);
//assert (mddb_importer_return != STILL_ACTIVE);

const std::string err_string = err.get();