signal.c

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#include <xinu.h>

syscall signal(sid32 sem)
{
    intmask mask;          /* Saved interrupt mask      */
    struct sentry *semptr; /* Ptr to sempahore table entry  */

    mask = disable();
    if (isbadsem(sem))
    {
        restore(mask);
        return SYSERR;
    }
    semptr = &semtab[sem];
    if (semptr->sstate == S_FREE)
    {
        restore(mask);
        return SYSERR;
    }
    if ((semptr->scount++) < 0)
    { /* Release a waiting process */
        ready(dequeue(semptr->squeue));
    }
    restore(mask);
    return OK;
}