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/* resched.c  -  resched */

#include <conf.h>
#include <kernel.h>
#include <proc.h>
#include <q.h>

/*------------------------------------------------------------------------
 * resched  --  reschedule processor to highest priority ready process
 *
 * Notes:	Upon entry, currpid gives current process id.
 *		Proctab[currpid].pstate gives correct NEXT state for
 *			current process if other than PRREADY.
 *------------------------------------------------------------------------
 */
int	resched()
{
	register struct	pentry	*optr;	/* pointer to old process entry */
	register struct	pentry	*nptr;	/* pointer to new process entry */

	/* no switch needed if current process priority higher than next*/

	if ( ( (optr= &proctab[currpid])->pstate == PRCURR) &&
	   (lastkey(rdytail)<optr->pprio)) {
		return(OK);
	}

	/* force context switch */

	if (optr->pstate == PRCURR) {
		optr->pstate = PRREADY;
		insert(currpid,rdyhead,optr->pprio);
	}

	/* remove highest priority process at end of ready list */

	nptr = &proctab[ (currpid = getlast(rdytail)) ];
	nptr->pstate = PRCURR;		/* mark it currently running	*/
#ifdef	RTCLOCK
	preempt = QUANTUM;		/* reset preemption counter	*/
#endif
	ctxsw(optr->pregs,nptr->pregs);

	/* The OLD process returns here when resumed. */

	return(OK);
}

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