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53 lines
1.2 KiB
53 lines
1.2 KiB
6 years ago
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/* queue.c - enqueue, dequeue */
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#include <xinu.h>
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struct qentry queuetab[NQENT]; /* Table of process queues */
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/*------------------------------------------------------------------------
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* enqueue - Insert a process at the tail of a queue
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*------------------------------------------------------------------------
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*/
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pid32 enqueue(
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pid32 pid, /* ID of process to insert */
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qid16 q /* ID of queue to use */
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)
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{
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qid16 tail, prev; /* Tail & previous node indexes */
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if (isbadqid(q) || isbadpid(pid)) {
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return SYSERR;
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}
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tail = queuetail(q);
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prev = queuetab[tail].qprev;
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queuetab[pid].qnext = tail; /* Insert just before tail node */
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queuetab[pid].qprev = prev;
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queuetab[prev].qnext = pid;
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queuetab[tail].qprev = pid;
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return pid;
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}
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/*------------------------------------------------------------------------
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* dequeue - Remove and return the first process on a list
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*------------------------------------------------------------------------
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*/
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pid32 dequeue(
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qid16 q /* ID of queue to use */
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)
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{
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pid32 pid; /* ID of process removed */
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if (isbadqid(q)) {
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return SYSERR;
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} else if (isempty(q)) {
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return EMPTY;
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}
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pid = getfirst(q);
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queuetab[pid].qprev = EMPTY;
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queuetab[pid].qnext = EMPTY;
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return pid;
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}
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