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Annotation of xinu/sys/screate.c, revision 1.1

1.1     ! root        1: /* screate.c - screate, newsem */
        !             2: 
        !             3: #include <conf.h>
        !             4: #include <kernel.h>
        !             5: #include <proc.h>
        !             6: #include <q.h>
        !             7: #include <sem.h>
        !             8: 
        !             9: /*------------------------------------------------------------------------
        !            10:  * screate  --  create and initialize a semaphore, returning its id
        !            11:  *------------------------------------------------------------------------
        !            12:  */
        !            13: SYSCALL screate(count)
        !            14:        int     count;                  /* initial count (>=0)          */
        !            15: {
        !            16:        PStype  ps;
        !            17:        int     sem;
        !            18: 
        !            19:        disable(ps);
        !            20:        if ( count<0 || (sem=newsem())==SYSERR ) {
        !            21:                restore(ps);
        !            22:                return(SYSERR);
        !            23:        }
        !            24:        semaph[sem].semcnt = count;
        !            25:        /* sqhead and sqtail were initialized at system startup */
        !            26:        restore(ps);
        !            27:        return(sem);
        !            28: }
        !            29: 
        !            30: /*------------------------------------------------------------------------
        !            31:  * newsem  --  allocate an unused semaphore and return its index
        !            32:  *------------------------------------------------------------------------
        !            33:  */
        !            34: LOCAL  newsem()
        !            35: {
        !            36:        int     sem;
        !            37:        int     i;
        !            38: 
        !            39:        for (i=0 ; i<NSEM ; i++) {
        !            40:                sem=nextsem--;
        !            41:                if (nextsem < 0)
        !            42:                        nextsem = NSEM-1;
        !            43:                if (semaph[sem].sstate==SFREE) {
        !            44:                        semaph[sem].sstate = SUSED;
        !            45:                        return(sem);
        !            46:                }
        !            47:        }
        !            48:        return(SYSERR);
        !            49: }

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