ptrecv.c

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#include <xinu.h>

uint32 ptrecv(int32 portid)
{
    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;
}