svsem/svsem_setall.c

This is svsem/svsem_setall.c (Listing 47-4, page 974), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* svsem_setall.c

   Usage: svsem_setall semid value...

   Set the values of all of the members of a System V semaphore set according
   to the values supplied on the command line.
*/
#include <sys/types.h>
#include <sys/sem.h>
#include "semun.h"                      /* Definition of semun union */
#include "tlpi_hdr.h"
int
main(int argc, char *argv[])
{
    struct semid_ds ds;
    union semun arg;                    /* Fourth argument for semctl() */
    int j, semid;

    if (argc < 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s semid val...\n", argv[0]);

    semid = getInt(argv[1], 0, "semid");

    /* Obtain size of semaphore set */

    arg.buf = &ds;
    if (semctl(semid, 0, IPC_STAT, arg) == -1)
        errExit("semctl");

    /* The number of values supplied on the command line must match the
       number of semaphores in the set */

    if (ds.sem_nsems != argc - 2)
        cmdLineErr("Set contains %ld semaphores, but %d values were supplied\n",
                (long) ds.sem_nsems, argc - 2);

    /* Set up array of values; perform semaphore initialization */

    arg.array = calloc(ds.sem_nsems, sizeof(arg.array[0]));
    if (arg.array == NULL)
        errExit("calloc");

    for (j = 2; j < argc; j++)
        arg.array[j - 2] = getInt(argv[j], 0, "val");

    if (semctl(semid, 0, SETALL, arg) == -1)
        errExit("semctl-SETALL");
    printf("Semaphore values changed (PID=%ld)\n", (long) getpid());

    exit(EXIT_SUCCESS);
}

 

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