#include "pcsem.h"
|
|
|
int pcsem::init(key_t key, unsigned int value) {
|
int semid, perms;
|
|
perms = S_IRUSR | S_IWUSR;
|
|
semid = semget(key, 1, IPC_CREAT | IPC_EXCL | perms);
|
|
if (semid != -1) { /* Successfully created the semaphore */
|
union semun arg;
|
struct sembuf sop;
|
|
fprintf(stderr, "%ld: created semaphore\n", (long) getpid());
|
|
arg.val = 0; /* So initialize it to 0 */
|
if (semctl(semid, 0, SETVAL, arg) == -1)
|
err_exit(errno, "semctl 1");
|
fprintf(stderr, "%ld: initialized semaphore\n", (long) getpid());
|
|
/* Perform a "no-op" semaphore operation - changes sem_otime
|
so other processes can see we've initialized the set. */
|
|
sop.sem_num = 0; /* Operate on semaphore 0 */
|
sop.sem_op = value;
|
sop.sem_flg = 0;
|
if (semop(semid, &sop, 1) == -1)
|
err_exit(errno, "semop");
|
fprintf(stderr, "%ld: completed dummy semop()\n", (long) getpid());
|
|
} else { /* We didn't create the semaphore set */
|
|
if (errno != EEXIST) { /* Unexpected error from semget() */
|
err_exit(errno, "semget 1");
|
|
} else { /* Someone else already created it */
|
const int MAX_TRIES = 10;
|
int j;
|
union semun arg;
|
struct semid_ds ds;
|
|
semid = semget(key, 1, perms); /* So just get ID */
|
if (semid == -1)
|
err_exit(errno, "semget 2");
|
|
fprintf(stderr, "%ld: got semaphore key\n", (long) getpid());
|
/* Wait until another process has called semop() */
|
|
arg.buf = &ds;
|
for (j = 0; j < MAX_TRIES; j++) {
|
fprintf(stderr, "Try %d\n", j);
|
if (semctl(semid, 0, IPC_STAT, arg) == -1)
|
err_exit(errno, "semctl 2");
|
|
if (ds.sem_otime != 0) /* Semop() performed? */
|
break; /* Yes, quit loop */
|
sleep(1); /* If not, wait and retry */
|
}
|
|
if (ds.sem_otime == 0) /* Loop ran to completion! */
|
err_exit(errno, "Existing semaphore not initialized");
|
}
|
}
|
return semid;
|
}
|
|
|
/* Reserve semaphore (blocking), return 0 on success, or -1 with 'errno'
|
set to EINTR if operation was interrupted by a signal handler */
|
|
/* Reserve semaphore - decrement it by 1 */
|
int pcsem::dec(int semId)
|
{
|
struct sembuf sops;
|
|
sops.sem_num = 0;
|
sops.sem_op = -1;
|
sops.sem_flg = 0;
|
|
while (semop(semId, &sops, 1) == -1)
|
if (errno != EINTR )
|
return -1;
|
|
return 0;
|
}
|
|
int pcsem::dec_nowait(int semId)
|
{
|
struct sembuf sops;
|
|
sops.sem_num = 0;
|
sops.sem_op = -1;
|
sops.sem_flg = IPC_NOWAIT;
|
|
while (semop(semId, &sops, 1) == -1)
|
if (errno != EINTR )
|
return -1;
|
|
return 0;
|
}
|
|
int pcsem::dec_timeout(int semId, struct timespec * timeout)
|
{
|
struct sembuf sops;
|
|
sops.sem_num = 0;
|
sops.sem_op = -1;
|
sops.sem_flg = 0;
|
|
while ( semtimedop(semId, &sops, 1, timeout) == -1)
|
if (errno != EINTR )
|
return -1;
|
|
return 0;
|
}
|
|
|
|
/* Release semaphore - increment it by 1 */
|
int pcsem::inc(int semId)
|
{
|
struct sembuf sops;
|
|
sops.sem_num = 0;
|
sops.sem_op = 1;
|
sops.sem_flg = 0;
|
|
return semop(semId, &sops, 1);
|
}
|
|
void pcsem::remove(int semid) {
|
union semun dummy;
|
if (semctl(semid, 0, IPC_RMID, dummy) == -1)
|
err_exit(errno, "semctl");
|
|
}
|
