The Linux Programming Interface

974 Chapter 47

if (argc != 2 || strcmp(argv[1], "--help") == 0)

usageErr("%s semid\n", argv[0]);

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

arg.buf = &ds;

if (semctl(semid, 0, IPC_STAT, arg) == -1)

errExit("semctl");

printf("Semaphore changed: %s", ctime(&ds.sem_ctime));

printf("Last semop(): %s", ctime(&ds.sem_otime));

/* Display per-semaphore information */

arg.array = calloc(ds.sem_nsems, sizeof(arg.array[0]));

if (arg.array == NULL)

errExit("calloc");

if (semctl(semid, 0, GETALL, arg) == -1)

errExit("semctl-GETALL");

printf("Sem # Value SEMPID SEMNCNT SEMZCNT\n");

for (j = 0; j < ds.sem_nsems; j++)

printf("%3d %5d %5d %5d %5d\n", j, arg.array[j],

semctl(semid, j, GETPID, dummy),

semctl(semid, j, GETNCNT, dummy),

semctl(semid, j, GETZCNT, dummy));

exit(EXIT_SUCCESS);

}

–––––––––––––––––––––––––––––––––––––––––––––––––––––––– svsem/svsem_mon.c

Initializing all semaphores in a set

The program in Listing 47-4 provides a command-line interface for initializing all

of the semaphores in an existing set. The first command-line argument is the iden-

tifier of the semaphore set to be initialized. The remaining command-line argu-

ments specify the values to which the semaphores are to be initialized (there must

be as many of these arguments as there are semaphores in the set).

Listing 47-4: Using the SETALL operation to initialize a System V semaphore set

––––––––––––––––––––––––––––––––––––––––––––––––––––– svsem/svsem_setall.c

#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;