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### semstat: A semtool companion program

As an added bonus, the source code to a companion program called `semstat` is provided next. The `semstat` program displays the values of each of the semaphores in the set created by `semtool`.

    /*****************************************************************************
      Excerpt from "Linux Programmer's Guide - Chapter 6"
      (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 <stdio.h>
     #include <stdlib.h>
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/sem.h>

     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(".", 's');

             /* Open the semaphore set - do not create! */
             if((semset_id = semget(key, 1, 0666)) == -1)
             {
                     printf("Semaphore set does not exist\n");
                     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 < maxsems) {
                     semval = semctl(sid, cntr, GETVAL, 0);
                     printf("Semaphore #%d:  --> %d\n", 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 = &mysemds;

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

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

     void dispval(int sid)
     {
             int semval;

             semval = semctl(sid, 0, GETVAL, 0);
             printf("semval is %d\n", semval);
     }