Desktop/xinu_mips-1.0.2.tar/xinu_mips-1.0.2/system/queue.c

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/* Embedded XINU, Copyright (C) 2007.  All rights reserved. */

#include <proc.h>
#include <queue.h>

struct  qentry queuetab[NQENT]; 
static  int nextqueue = NPROC;  
short enqueue(short pid, queue q)
{
        int tail;

        if (isbadqueue(q) || isbadpid(pid))
        { return SYSERR; }

        tail = queuetail(q);

        queuetab[pid].next = tail;
        queuetab[pid].prev = queuetab[tail].prev;
        queuetab[queuetab[tail].prev].next = pid;
        queuetab[tail].prev = pid;
        return pid;
}


short remove(short pid)
{
        if (isbadpid(pid)) { return SYSERR; }

        queuetab[queuetab[pid].prev].next = queuetab[pid].next;
        queuetab[queuetab[pid].next].prev = queuetab[pid].prev;
        return pid;
}

short dequeue(queue q)
{
        int head = queuehead(q);
        int pid;                    /* first process on the list    */

        if (isbadqueue(q)) { return SYSERR; }

        if ((pid = queuetab[head].next) < NPROC)
        { 
                remove(pid);
                queuetab[pid].prev = pid;
                queuetab[pid].next = pid;
                return pid; 
        }
        else
        { return EMPTY; }
}

queue newqueue(void)
{
        int head, tail;

        head = nextqueue++;
        tail = nextqueue++;
        queuetab[head].next = tail;
        queuetab[head].prev = EMPTY;
        queuetab[tail].next = EMPTY;
        queuetab[tail].prev = head;
        return (queue) ((head << 16) | (tail & 0xFFFF));
}

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