Creating Named Pipe Error

Question

I am creating a named pipe and using a function to do so. Here is the code:

HANDLE              tProviderPipe(INVALID_HANDLE_VALUE);
SECURITY_ATTRIBUTES tSecurityAttributes;

tSecurityAttributes.nLength = sizeof(tSecurityAttributes);
tSecurityAttributes.bInheritHandle = FALSE;
tSecurityAttributes.lpSecurityDescriptor = NULL;
while (1)
{
    tProviderPipe = ::CreateNamedPipe(L"\\\\.\\pipe\\MyPipe",
                                      PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED,
                                      PIPE_TYPE_BYTE | PIPE_READMODE_BYTE | PIPE_WAIT,
                                      1,
                                      128,
                                      128,
                                      5000,
                                      &tSecurityAttributes);

    if (INVALID_HANDLE_VALUE != tProviderPipe)
    {
        DWORD lLastStatus(GetLastError());
        OHTRACE(Trace::eTAlways, L"Pipe Status: " << (unsigned int)lLastStatus);
        break;
    }
    if (ERROR_PIPE_BUSY != GetLastError())
    {
        DWORD lLastStatus(GetLastError());
        OHTRACE(Trace::eTAlways, L"Pipe Status: " << (unsigned int)lLastStatus);
        break;
    }
    if (!WaitNamedPipe(L"MyPipe", 20000))
    {
        DWORD lLastStatus(GetLastError());
        OHTRACE(Trace::eTAlways, L"WPipe Status: " << (unsigned int)lLastStatus);
    }

When this function is called the pipe creation fails with error code 231 (ie Pipe busy). I don't understand why the pipe is busy and what is the correct way to create pipe? What should be the post checks and pre-checks before going forward to creating a pipe?

Answer 1

The code you showed is all wrong.

This check:

if (INVALID_HANDLE_VALUE != tProviderPipe)

Needs to use == instead of != . Your code is failing if CreateNamedPipe() succeeds .

This check:

if (ERROR_PIPE_BUSY != GetLastError())

Needs to be removed. First, it is in the wrong place. GetLastError() is only valid if CreateNamedPipe() fails . After making the == fix above, then GetLastError() will never be ERROR_PIPE_BUSY (or any other meaningful value) after CreateNamedPipe() succeeds. Second, if you move it into the if that is checking tProviderPipe then it becomes redundant since it is logging the same info that is already being logged there.

This check:

if (!WaitNamedPipe(L"MyPipe", 20000))

Also needs to be removed. First, you are passing it the wrong pipe name format. Second, it is intended for a named pipe client to call before calling CreateFile() (or if CreateFile() fails with ERROR_PIPE_BUSY ). Do not call it in your named pipe server . You meant to call ConnectNamedPipe() instead, which waits for a client to connect to the server pipe you are creating.

Please look at the named pipe server examples on MSDN.

Try something more like this instead:

HANDLE tProviderPipe = INVALID_HANDLE_VALUE;
SECURITY_ATTRIBUTES tSecurityAttributes;
OVERLAPPED ov = {};
DWORD lLastStatus;

ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (!ov.hEvent) {
    lLastStatus = GetLastError();
    OHTRACE(Trace::eTAlways, L"Pipe Event Create Error: " << (UINT)lLastStatus);
    return;
}

tSecurityAttributes.nLength = sizeof(tSecurityAttributes);
tSecurityAttributes.bInheritHandle = FALSE;
tSecurityAttributes.lpSecurityDescriptor = NULL;

while (1) {
    if (INVALID_HANDLE_VALUE == tProviderPipe) {
        tProviderPipe = ::CreateNamedPipe(L"\\\\.\\pipe\\MyPipe", PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED, PIPE_TYPE_BYTE | PIPE_READMODE_BYTE | PIPE_WAIT, 1, 128, 128, 5000, &tSecurityAttributes);
        if (INVALID_HANDLE_VALUE == tProviderPipe) {
            lLastStatus = GetLastError();
            OHTRACE(Trace::eTAlways, L"Pipe Create Error: " << (UINT)lLastStatus);
            break;
        }
    }

    if (!ConnectNamedPipe(tProviderPipe, &ov)) {
        lLastStatus = GetLastError();
        if (ERROR_IO_PENDING == lLastStatus) {
            if (WaitForSingleObject(ov.hEvent, 20000) != WAIT_OBJECT_0) {
                OHTRACE(Trace::eTAlways, L"Pipe not connected in 20 seconds");
                break;
            }
        }
        else if (ERROR_PIPE_CONNECTED != lLastStatus) {
            OHTRACE(Trace::eTAlways, L"Pipe Connect Error: " << (UINT)lLastStatus);
            continue;
        }
    }

    // use tProviderPipe as needed ...

    DisconnectNamedPipe(tProviderPipe);
}

if (INVALID_HANDLE_VALUE != tProviderPipe) {
    CloseHandle(tProviderPipe);
}

CloseHandle(ov.hEvent);