Managing shared memory lookups

I have a program that loads a very large avl tree and then opens a shared memory area and waits for requests (with semaphores to order the queueing). The client program connects to the shared memory area on startup but I would like it to check the status of the shared memory before each request. I have had instances where the client program seems to get stuck (for want of a better word) waiting for a reply. I am using Posix shared memory.

The code for connecting to the shared memory area is:

Code:

---

    /* open and map shared memory that server must create */
    FILE_DESC = shm_open(SHM_NAME, O_RDWR, 0666);
    if ( FILE_DESC < 0 )
    {
                /* An error occurred, exit function */
                TRACE(("SHM Message: Error occurred opening shared memory exiting\n"));
                return(0);
    }
    SHARED_MEM_PTR = mmap(NULL, sizeof(SHM_STRUCT), PROT_READ | PROT_WRITE, MAP_SHARED, FILE_DESC, 0);
    if ( SHARED_MEM_PTR < 0 )
    {
                /* An error occurred, exit function */
            TRACE(("SHM Message: Error mapping shared file exiting\n"));
                return(0);
    }
    /* Shared memory successfully attached to, set global variable to true */
    SETTINGS.SHARED_MEM = TRUE;
    TRACE(("SHM Message: Shared memory successfully created\n"));
    /* Now exit successfully */
    return(1);

---

And the code for issueing request is:

Code:

---

        if ((SETTINGS.CDR_WRITE_ICF || SETTINGS.CDR_SHOW_ICF) && SETTINGS.SHARED_MEM)
        {
            /* Currently we have to assume that shared memory is available and proceeed
            * as normal.
            */
                /* UL-CR6572 Need to ensure that 11 characters are passed to the search engine and that
                * it is left padded with zeros especially for authcodes
                */
                sprintf( ptr->BillNumber, "%011s", ptr->billing_number ); /* UL-CR6572 */
            sem_wait(&SHARED_MEM_PTR->ControlSem);
            strcpy(SHARED_MEM_PTR->SrchCliNum, ptr->BillNumber);
            sem_post(&SHARED_MEM_PTR->RequestSem);
            sem_wait(&SHARED_MEM_PTR->AnswerSem);
            strcat(ptr->AccountNumber, SHARED_MEM_PTR->RtrnAcctNum);
            sem_post(&SHARED_MEM_PTR->ControlSem);
        }

---

Thanks