Using Select() with the Alert Socket

The alert socket is used to communicate messages from the RSVP daemon to the API. These messages generally turn into events for the program. The select() call is used to wait for read data on the alert socket. Once there is read data available, the program must call rapi_dispatch() so that the RSVP API can read the data and handle it properly. Typically, rapi_dispatch() will, in turn, call your callback function, possibly more than once.

In the <RSVPRAPI.H> header file, the data type rapi_event_rtn_t is declared to be a pointer to a callback function. The arguments of the function are also declared there, so that you can see how to declare your callback function arguments.

This example shows a loop with a select() call waiting on the alert socket until a path message is received and handled by a callback function:

fd_set readSockets;
    int rc, rapi_rc;
    int receivedPathEvent = 0; /* set to 1 by the callback routine */

    while (! receivedPathEvent)
        {
        FD_ZERO(&readSockets);
        FD_SET(alertSoc, &readSockets);
        if ((rc = select(FD_SETSIZE, &readSockets, NULL, NULL, &timeout)) < 0)
            {
            psock_errno("select() on alert socket");
            exit(1);
            }
        if (rc > 0 && FD_ISSET(alertSoc, &readSockets))
            {
            rapi_rc = rapi_dispatch();
            if (rapi_rc == RAPI_ERR_NORSVP)
                {
                printf("Warning! RSVP has gone away.\n");
                exit(1);
                }
            }
        } /* end while */

Waiting for a reservation message would be handled similarly.