int server(void)
{
int s = mseminit(SEM0, 0600, 2, 0, 1);
if (s == -1) {
perror("mseminit");
return 1;
}
int cnt = 1;
for (int i = 0; i < 5; ++i) {
if (mP(s, 1, 0) != 0) {
if (errno == EINTR) {
/* interrupted by syscall, try again */
continue;
}
perror("mP(0)");
break;
}
printf("s%d", cnt);
cnt += 2;
fflush(stdout);
if (mV(s, 1, 1) != 0) {
perror("mV(1)");
break;
}
}
/* clean up semaphores */
if (msemrm(s) != 0) {
perror("msemrm");
}
return 0;
}
/** Initialize all variables needed for ipc */
static void ipc_init(void)
{
/* All communicating processes need to be started from within the ssame working dir in order to make key have the same value */
key_t key = ftok(".", 'x');
if(key == -1) {
bail_out(EXIT_FAILURE, "Couldn't create ipc key via ftok");
}
/* cnd is a two field semaphore (0 = write, 1 = read)*/
if((cnd = mseminit(key, (0600), 2, 1, 0)) == -1) {
if((cnd = msemgrab(key, 2)) == -1) {
bail_out(EXIT_FAILURE, "Error aquiring conditional semephores");
}
}
/* mtx is a mutex semaphore to protect access to shm */
if((mtx = seminit(key + 1, (0600), 0)) == -1) {
if((mtx = semgrab(key + 1)) == -1) {
bail_out(EXIT_FAILURE, "Error aquiring mutual exclusive semephore");
}
}
/* Create or fetch shm segment */
if((shm = shmget(key, sizeof(ipc_data_t), IPC_CREAT | IPC_EXCL | (0600))) == -1) {
if((shm = shmget(key, sizeof(ipc_data_t), 0)) == -1) {
bail_out(EXIT_FAILURE, "Error aquiring shared mem");
}
/* The process that creates the shm segment will up the mtx, after it's initialized */
if(semdown(mtx) == -1) {
bail_out(EXIT_FAILURE, "Error downing mutex");
}
/* Mount shm */
if((shared = shmat(shm, NULL, 0)) == (void *) -1) {
bail_out(EXIT_FAILURE, "Error attaching shm segment");
}
#ifndef _BUILD_READIN
/* Signal listening reader */
shared->flag |= READER_F;
#endif
/* Let other processes proceed */
if(semup(mtx) == -1) {
bail_out(EXIT_FAILURE, "Error upping mutex");
}
} else {
/* Mount shm */
if((shared = shmat(shm, NULL, 0)) == (void *) -1) {
bail_out(EXIT_FAILURE, "Error attaching shm segment (creator)");
}
/* If we created the segment, we'll initialize it */
(void) memset(shared, 0, sizeof(ipc_data_t));
#ifndef _BUILD_READIN
/* Signal listening reader */
shared->flag |= READER_F;
#endif
/* And signal other processes to proceed */
if(semup(mtx) == -1) {
bail_out(EXIT_FAILURE, "Error opening mutex");
}
}
}
