c++ - ReadFile 使用 NamedPipe block 虽然使用重叠

Question

我正在使用 NamedPipes 在我们的 Windows 应用程序的不同模块之间进行通信。在某一时刻，读取操作可能需要很长时间，所以我们想添加一个超时。我像这样添加了 OVERLAPPED 标志:

pipeHandle = CreateFile(
            pipename,
            PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED,
            0,
            nullptr,
            OPEN_EXISTING,
            0,
            nullptr);

那么读取操作是这样的:

    OVERLAPPED overlapped;
        ZeroMemory(&overlapped, sizeof(OVERLAPPED));
        overlapped.hEvent = CreateEvent(nullptr, TRUE, FALSE, nullptr);
    successful = ReadFile(
            pipeHandle,
            buffer,
            4096 * sizeof(wchar_t),
            &numBytesRead,
            &overlapped
        );
    if (successful == FALSE)
    {
        LOG("Reading was not successful");
        if (GetLastError() != ERROR_IO_PENDING)
        {
            // The function call failed. ToDo: recovery.
            LOG_LAST_ERROR("Failed because of Error: ");
            return ERROR_READ_FAULT;
        }
        else
        {
            // TODO: add a timeout...
            successful = GetOverlappedResult(pipeHandle, &overlapped, &numBytesRead, TRUE);
        }
    }
    else
    {
        LOG("Reading was successful");
        // I/O completed:
        return ERROR_SUCCESS;
    }

现在我希望对 ReadFile 的调用会立即返回，这样我就可以处理可能的超时，但它会阻塞直到调用返回。

我做错了什么？

Answer 1

在您的代码中，FILE_FLAG_OVERLAPPED 在 dwDesiredAccess 参数中，但它应该在 dwFlagsAndAttributes 参数中指定。

所以，这可能会更好:

pipeHandle = CreateFile(
        pipename,
        PIPE_ACCESS_DUPLEX,
        0,
        nullptr,
        OPEN_EXISTING,
        FILE_FLAG_OVERLAPPED,
        nullptr);