/* ptrecv.c - ptrecv */

#include 

/*------------------------------------------------------------------------
 *  ptrecv  -  Receive a message from a port, blocking if port empty
 *------------------------------------------------------------------------
 */
uint32  ptrecv(
          int32         portid          /* ID of port to use            */
        )
{
        intmask mask;                   /* Saved interrupt mask         */
        struct  ptentry *ptptr;         /* Pointer to table entry       */
        int32   seq;                    /* Local copy of sequence num.  */
        umsg32  msg;                    /* Message to return            */
        struct  ptnode  *msgnode;       /* First node on message list   */

        mask = disable();
        if ( isbadport(portid) ||
             (ptptr= &porttab[portid])->ptstate != PT_ALLOC ) {
                restore(mask);
                return (uint32)SYSERR;
        }

        /* Wait for message and verify that the port is still allocated */

        seq = ptptr->ptseq;             /* Record orignal sequence      */
        if (wait(ptptr->ptrsem) == SYSERR || ptptr->ptstate != PT_ALLOC
            || ptptr->ptseq != seq) {
                restore(mask);
                return (uint32)SYSERR;
        }

        /* Dequeue first message that is waiting in the port */

        msgnode = ptptr->pthead;
        msg = msgnode->ptmsg;
        if (ptptr->pthead == ptptr->pttail)     /* Delete last item     */
                ptptr->pthead = ptptr->pttail = NULL;
        else
                ptptr->pthead = msgnode->ptnext;
        msgnode->ptnext = ptfree;               /* Return to free list  */
        ptfree = msgnode;
        signal(ptptr->ptssem);
        restore(mask);
        return msg;
}