ReadMsgQueue Returns ERROR_INVALID_PARAMETER

Question

Windows Embedded Compact.

Trying to send and receive a message with MsgQueue.

Looks like the write is working but read gives the incorrect parameters error.

Any ideas what is missing?

I am not sure about the create queue function. It says that it must be called twice to get a read or write handle - is this right ?

    int main()
    {



        MSGQUEUEOPTIONS options = {0};

        options.dwSize = sizeof(options); // 
        options.dwFlags = MSGQUEUE_NOPRECOMMIT;
        options.dwMaxMessages = 10000; // msg max for queue
        options.cbMaxMessage = 50; // max number of bytes in each msg





        options.bReadAccess = TRUE; // read
        HANDLE hRead = CreateMsgQueue(LPCWSTR("MSG_QUEUE"), &options);
        if ( hRead == NULL )
        {
            printf("CreateMsgQueue hRead failed! Err code: %d\n", GetLastError());
        }

        // Thread A will read msg queue
        HANDLE hTg = CreateThread(NULL, 0, threadA, hRead, 0, 0);
        if ( NULL == hTg )   
        {
            printf("CreateThread failed - A!\n");
            return 1;
        }

        Sleep(1000); //give time before sending msg


        options.bReadAccess = FALSE; // write to
        HANDLE hWrte = CreateMsgQueue(LPCWSTR("MSG_QUEUE"), &options);
        if ( hWrte == NULL )
        {
            printf("CreateMsgQueue hWrte failed! Err code: %d\n", GetLastError());
        }

        // Thread B write to queue
        HANDLE hTt = CreateThread(NULL, 0, threadB, hWrte, 0, 0);
        if ( NULL == hTt )   
        {
            printf("CreateThread failed - B!\n");
            return 1;
        }
        // quit on <ENTER> key
        getchar();

}

DWORD WINAPI threadB(LPVOID lpParameter)
{
    HANDLE msgH = HANDLE(lpParameter);
    if ( msgH == NULL)
    {
        printf("Null handle in write!\n");
    }

    char message[10] = "ABCDEFGHI";

    printf("Size of message sent: %d bytes\n", sizeof(message));


    // know that a queue is not full and that it's safe to write
    WaitForSingleObject(msgH, INFINITE);

    BOOL ret = WriteMsgQueue(
        msgH,
        &message, 
        sizeof(message),
        INFINITE,
        NULL);
    if ( ret == FALSE )
    {
        printf("WriteMsgQueue failed! Err code: %d\n", GetLastError());
    }

    return 0;
}

DWORD WINAPI threadA(LPVOID lpParameter)
{
    HANDLE hQ = HANDLE(lpParameter);
    if ( hQ == NULL )
    {
        printf("null handle in read!\n");
    }

    char readIn[50] = {0};
    LPDWORD  numRead = 0;
    //DWORD flag;

    // need to wait on sinfle object
    WaitForSingleObject(hQ, INFINITE);

    BOOL ret = ReadMsgQueue(
        hQ,
        &readIn,
        DWORD(sizeof(readIn)),
        numRead,
        INFINITE,
        NULL
        );

    if ( ret == FALSE )
    {
        printf(" ReadMsgQueue failed! Err code: %d\n", GetLastError());
    }

    printf("Size received: %d\n", numRead);
    printf("Msg Received: %s\n", readIn);


    return 0;
}

EDIT

Here is the working Read Function after @WhozCraig and another issue found incase anyone else needs this:

DWORD WINAPI threadA(LPVOID lpParameter)
{
    HANDLE hQ = HANDLE(lpParameter);
    if ( hQ == NULL )
    {
        printf("null handle in read!\n");
    }

    char readIn[50] = {0};
    DWORD  numRead = 0;
    DWORD flag;

    // need to wait on sinfle object
    WaitForSingleObject(hQ, INFINITE);

    BOOL ret = ReadMsgQueue(
        hQ,
        &readIn,
        sizeof(readIn),
        &numRead,
        INFINITE,
        &flag
        );

    if ( ret == FALSE )
    {
        printf(" ReadMsgQueue failed! Err code: %d\n", GetLastError());
    }

    printf("Size received: %d\n", numRead);
    printf("Msg Received: %s\n", readIn);

    return 0;
}

Answer 1

Yes, that is how you setup a message queue fro sending/receiving. Two opens are generally used.

I believe the problem with your ReadMsgQueue() invocation is the received-size parameter. It is a LPDWORD, and must not be NULL. you're currently doing this:

char readIn[50] = {0};
LPDWORD  numRead = 0; // SHOULD NOT BE A POINTER

// need to wait on sinfle object
WaitForSingleObject(hQ, INFINITE);

BOOL ret = ReadMsgQueue(
    hQ,
    &readIn,
    DWORD(sizeof(readIn)),
    numRead, // THIS IS A PROBLEM
    INFINITE,
    NULL
    );

You're passing NULL. You need to do this instead:

char readIn[50] = {0};
DWORD numRead = 0; // NOTE: regular DWORD

// need to wait on sinfle object
WaitForSingleObject(hQ, INFINITE);

BOOL ret = ReadMsgQueue(
    hQ,
    &readIn,
    DWORD(sizeof(readIn)),
    &numRead, // NOTE: address of DWORD
    INFINITE,
    NULL
    );

It is unclear to me whether the last parameter, the received message flags out-paramter can be NULL. It is not specifically called out in the documentation like the size-read DWORD address is, which clearly states This parameter cannot be NULL, as do other params. So your mileage may vary.