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Annotation of xinu/sys/preceive.c, revision 1.1.1.1

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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