/* ptcount.c - ptcount */

#include 

/*------------------------------------------------------------------------
 *  ptcount  -  Return the count of messages currently waiting in a port
 *                (a non-negative count K means the port contains K
 *                 K messages,  including messages from senders that
 *                 are blocked waiting to send a message; a count of
 *                 negative K means a port is empty and K processes
 *                 are blocked waiting to receive a message)
 *------------------------------------------------------------------------
 */
int32   ptcount(
          int32         portid          /* ID of a port to use          */
        )
{
        intmask mask;                   /* Saved interrupt mask         */
        int32   count;                  /* Count of messages available  */
        int32   sndcnt;                 /* Count of sender semaphore    */
        struct  ptentry *ptptr;         /* Pointer to port table entry  */

        mask = disable();
        if ( isbadport(portid) ||
                (ptptr= &porttab[portid])->ptstate != PT_ALLOC ) {
                        restore(mask);
                        return SYSERR;
        }

        /* Get count of messages available */

        count = semcount(ptptr->ptrsem);

        /* If messages are waiting, check for blocked senders */

        if (count >= 0) {
                sndcnt = semcount(ptptr->ptssem);
                if (sndcnt < 0) {       /* -sndcnt senders blocked */
                        count += -sndcnt;
                }
        }
        restore(mask);
        return count;
}