Named pipe in windows

Question

I'm trying to implement the communication between two processes via namedpipes. To be more precise (don't think it effects the question), I want two Matlab instances to communicate with each other.

It works ok so far, but in 10% of all cases, it says that there is another process at the end of the pipe...

My code (shortened) so far (sender):

pipe = CreateNamedPipe(uniquePipeName, // name of the pipe
    PIPE_ACCESS_DUPLEX, // 
    PIPE_TYPE_MESSAGE, // send data as a byte stream
    1, // only allow 1 instance of this pipe
    0, // no outbound buffer
    0, // no inbound buffer
    0, // use default wait time
    NULL // use default security attributes
    );
... some error handling...
result = ConnectNamedPipe(pipe, NULL);
if(!result)
{
    printerror()
    CloseHandle(pipe);
    return;
}
numBytesWritten = 0;
printf("Sending %lg\n", *uPtrs[0]);
result = WriteFile(pipe, // handle to our outbound pipe
    uPtrs[0], // data to send
    sizeof(double),

    &numBytesWritten, // will store actual amount of data sent
    NULL // not using overlapped IO
    );
if (!result) {
    printerror()
}
CloseHandle(pipe);

And the reciever:

    while(true)
{
    if (!WaitNamedPipe(uniquePipeName, NMPWAIT_USE_DEFAULT_WAIT))
        continue;   // timeout, try again
    pipe = CreateFile(
        uniquePipeName,
        GENERIC_READ, // only need read access
        0,//FILE_SHARE_READ,
        NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        NULL
        );
    if (pipe != INVALID_HANDLE_VALUE)
        break;
    else
    {
        {
            if (GetLastError() == ERROR_PIPE_BUSY || GetLastError() == 2)
            {
                FormatMessage(
                    FORMAT_MESSAGE_ALLOCATE_BUFFER | 
                    FORMAT_MESSAGE_FROM_SYSTEM |
                    FORMAT_MESSAGE_IGNORE_INSERTS,
                    NULL,
                    GetLastError(),
                    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                    (LPTSTR) &lpMsgBuf,
                    0, NULL );
                printf("%s\n",lpMsgBuf);
                CloseHandle(pipe);
                if (!WaitNamedPipe(uniquePipeName, NMPWAIT_USE_DEFAULT_WAIT))
                    continue;   // timeout, try again
            }
            else
            {
                printf("Failed to connect pipe. Error %.i\n",GetLastError());
                y[0] = 0;
                return;
            }
            //system("pause");
        }
    }
}
printf("Connected!\n");

result = ReadFile(
    pipe,
    &buffer_in, // the data from the pipe will be put here
    sizeof(double),
    //        127 * sizeof(wchar_t), // number of bytes allocated
    &numBytesRead, // this will store number of bytes actually read
    NULL // not using overlapped IO
    );


printf("Recieved: %lg\n",buffer_in);
printf("Recieved: %lg\n", buffer_out);

y[0] = buffer_in;
CloseHandle(pipe);

The error code in case of a failed submission is: GetLastError: 535 : There is a process on other end of the pipe.

As I'm totally new to the whole subjects, any other adivses to improve the core are appreciated.

Thanks a lot!

Answer 1

I know this question is from 2014, but I had the same issue and found the solution. In the Microsoft docs example (https://learn.microsoft.com/en-us/windows/win32/ipc/multithreaded-pipe-server) you can see that they check for the exact error message you get (535), in which case fConnected is set to true and the program continues. So I guess this error is actually a success?

fConnected = ConnectNamedPipe(hPipe, NULL) ? 
     TRUE : (GetLastError() == ERROR_PIPE_CONNECTED);