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

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

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

syscall wait(semaphore sem)
{
        irqmask ps;    
        struct sentry *psem;
        pcb *ppcb;

        ps = disable();              /* disable interrupts                   */
        if ( isbadsem(sem) )         /* safety check                         */
        {
                restore(ps);
                return SYSERR;
        }
        ppcb = &proctab[currpid];    /* retrieve pcb from process table      */
        psem = &semtab[sem];         /* retrieve semaphore entry             */
        if( --(psem->count) < 0 )    /* if requested resource is unavailable */
        {
                ppcb->state = PRWAIT;    /* set process state to PRWAIT          */
                ppcb->sem = sem;         /* record semaphore id in pcb           */
                enqueue(currpid, psem->queue);
                resched();               /* place in wait queue and reschedule   */
        }
        restore(ps);                 /* restore interrupts                   */
        return OK;
}

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