Querying Counts of Exceptions

Querying Counts of Exceptions

When you set a policy that permits exceptions, the FRS control process can query for counts of exceptions. This is done with a call to frs_getattr(), passing the handle to the Frame Scheduler, the number of the minor frame, and the process ID of the process within that frame.

The values returned in a structure of type frs_overrun_info_t are the counts of overrun and underrun exceptions incurred by that process in that minor frame. In order to find out the count of all overruns in a given minor frame, you must sum the counts for all processes queued to that frame. If a process is queued to more than one minor frame, separate counts are kept for it in each frame.

The function in Example 7-5 takes a Frame Scheduler handle and a minor frame number. It gets the list of process IDs queued to that that minor frame, and returns the sum of all exceptions for all of them.

Example 7-5 : Function to Return a Sum of Exception Counts

#define THE_MOST_PIDS 250
int
totalExcepts(frs_t * theFRS, int theMinor)
{
    int numPids = frs_getqueuelen(theFRS, theMinor);
    int j, sum;
    pid_t allPids[THE_MOST_PIDS];
    if ( (numPids <= 0) || (numPids > THE_MOST_PIDS) )
        return 0; /* invalid minor #, or no procs queued? */

    if (!frs_readqueue(theFRS, theMinor, allPids))
        return 0; /* unexpected problem with reading IDs */

    for (sum = j = 0; j<numPids; ++j)
    {
        frs_overrun_info_t work;
        frs_getattr(theFRS,            /* the scheduler */
                    theMinor,         /* the minor frame */
                    allPids[j],       /* the process */
                    FRS_ATTR_OVERRUNS, /* want counts */
                    &work);           /* put them here */
        sum += (work.overruns + work.underruns);
    }
    return sum;
}

Tip: If a function such as the one in Example 7-5 is to be called frequently, it is a good idea to prepare the arrays of process IDs once and save them. The repeated calls to frs_getqueuelen() and frs_readqueue() can be avoided.