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<B> Next:</B> <A NAME="tex2html1165" HREF="node65.html">6.4.4 Shared Memory</A>
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<H3><A NAME="SECTION00743700000000000000">semstat: A semtool companion program</A></H3>
<P>
As an added bonus, the source code to a companion program called <TT>semstat</TT>
is provided next.  The <TT>semstat</TT> program displays the values of each of the
semaphores in the set created by <TT>semtool</TT>.
<P>
<P>
<HR><PRE>/*****************************************************************************
 Excerpt from &quot;Linux Programmer's Guide - Chapter 6&quot;
 (C)opyright 1994-1995, Scott Burkett
 ***************************************************************************** 
 MODULE: semstat.c
 *****************************************************************************
 A companion command line tool for the semtool package.  semstat displays
 the current value of all semaphores in the set created by semtool.
 *****************************************************************************/

#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;sys/types.h&gt;
#include &lt;sys/ipc.h&gt;
#include &lt;sys/sem.h&gt;

int get_sem_count(int sid);
void show_sem_usage(int sid);
int get_sem_count(int sid);
void dispval(int sid);

int main(int argc, char *argv[])
{
        key_t key;
        int   semset_id;

        /* Create unique key via call to ftok() */
        key = ftok(&quot;.&quot;, 's');

        /* Open the semaphore set - do not create! */
        if((semset_id = semget(key, 1, 0666)) == -1) 
        {
                printf(&quot;Semaphore set does not exist\n&quot;);
                exit(1);
        }

        show_sem_usage(semset_id); 
        return(0);
}

void show_sem_usage(int sid)
{
        int cntr=0, maxsems, semval;

        maxsems = get_sem_count(sid);

        while(cntr &lt; maxsems) {
                semval = semctl(sid, cntr, GETVAL, 0);
                printf(&quot;Semaphore #%d:  --&gt; %d\n&quot;, cntr, semval);
                cntr++;
        }
}

int get_sem_count(int sid)
{
        int rc;
        struct semid_ds mysemds;
        union semun semopts;

        /* Get current values for internal data structure */
        semopts.buf = &amp;mysemds;

        if((rc = semctl(sid, 0, IPC_STAT, semopts)) == -1) {
                perror(&quot;semctl&quot;);
                exit(1);
        }

        /* return number of semaphores in set */
        return(semopts.buf-&gt;sem_nsems);
}

void dispval(int sid)
{
        int semval;

        semval = semctl(sid, 0, GETVAL, 0);
        printf(&quot;semval is %d\n&quot;, semval);
}</PRE> 
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<I>Converted on: <BR>
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