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Annotation of xinu/sys/preceive.c, revision 1.1

1.1     ! root        1: /* preceive.c - preceive */
        !             2: 
        !             3: #include <conf.h>
        !             4: #include <kernel.h>
        !             5: #include <mark.h>
        !             6: #include <ports.h>
        !             7: 
        !             8: /*------------------------------------------------------------------------
        !             9:  *  preceive  --  receive a message from a port, blocking if port empty
        !            10:  *------------------------------------------------------------------------
        !            11:  */
        !            12: SYSCALL        preceive(portid)
        !            13: int portid;
        !            14: {
        !            15:        PStype  ps;
        !            16:        struct  pt      *ptptr;
        !            17:        int     seq;
        !            18:        int     msg;
        !            19:        struct  ptnode  *nxtnode;
        !            20: 
        !            21:        disable(ps);
        !            22:        if ( isbadport(portid) ||
        !            23: #ifdef MEMMARK
        !            24:             unmarked(ptmark) ||
        !            25: #endif
        !            26:             (ptptr= &ports[portid])->ptstate != PTALLOC ) {
        !            27:                restore(ps);
        !            28:                return(SYSERR);
        !            29:        }
        !            30: 
        !            31:        /* wait for message and verify that the port is still allocated */
        !            32: 
        !            33:        seq = ptptr->ptseq;
        !            34:        if (wait(ptptr->ptrsem) == SYSERR || ptptr->ptstate != PTALLOC
        !            35:            || ptptr->ptseq != seq) {
        !            36:                restore(ps);
        !            37:                return(SYSERR);
        !            38:        }
        !            39: 
        !            40:        /* dequeue first message that is waiting in the port */
        !            41: 
        !            42:        nxtnode = ptptr->pthead;
        !            43:        msg = nxtnode->ptmsg;
        !            44:        if (ptptr->pthead == ptptr->pttail)     /* delete last item     */
        !            45:                ptptr->pthead = ptptr->pttail = (struct ptnode *) NULL;
        !            46:        else
        !            47:                ptptr->pthead = nxtnode->ptnext;
        !            48:        nxtnode->ptnext = ptfree;               /* return to free list  */
        !            49:        ptfree = nxtnode;
        !            50:        signal(ptptr->ptssem);
        !            51:        restore(ps);
        !            52:        return(msg);
        !            53: }

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