int main(int argc,char *argv)
{
pid_t pid;
int i;
int value;
key_t key;
int status;
if((pid=fork())==-1)
{
perror("fork");
exit(EXIT_FAILURE);
}
else if(pid==0)
{
if((sem_id=semget((key_t)123456,1,IPC_CREAT|0770))==-1)
{
perror("semget");
exit(EXIT_FAILURE);
}
if (!set_semvalue())
{
fprintf(stderr, "Failed to initialize semaphore\n");
exit(EXIT_FAILURE);
}
value=get_semvalue();
printf("this is child,the current value is %d\n",value);
if(!semaphore_v())
{
fprintf(stderr, "Failed to v operator\n");
exit(EXIT_FAILURE);
}
value=get_semvalue();
printf("the child %d V operator,value=%d\n",i,value);
printf("child exit success\n");
exit(EXIT_SUCCESS);
}
else //parent
{
sleep(3);
if((sem_id=semget((key_t)123456,1,IPC_CREAT|0770))==-1)
{
perror("semget");
exit(EXIT_FAILURE);
}
value=get_semvalue();
printf("this is parent ,the current value is %d\n",value);
printf("the parent will remove the sem\n");
if(semctl(sem_id,0, IPC_RMID,(struct msquid_ds*)0)==-1)
{
perror("semctl");
exit(EXIT_FAILURE);
}
return 0;
}
}
int main(int argc, char *argv[])
{
pid_t pid;
int value;
key_t key;
if((pid=fork()) == -1){
perror("fork");
exit(EXIT_FAILURE);
}else if (pid == 0){
if((sem_id=semget((key_t)123456, 1, 0770|IPC_CREAT)) == -1){
perror("semget");
exit(EXIT_FAILURE);
}
if(!set_semvalue()){
printf("failed initialized semaphore\n");
exit(EXIT_FAILURE);
}
value = get_semvalue();
printf("child: the current value is %d\n",value);
if(!semaphore_v()){
printf("failed to v operator\n");
exit(EXIT_FAILURE);
}
value = get_semvalue();
printf("child: v operator, value=%d\n", value);
printf("child: exit success\n");
exit(EXIT_SUCCESS);
}else{
sleep(3);
if((sem_id = semget((key_t)123456, 1, 0770|IPC_CREAT)) == -1){
perror("semget");
exit(EXIT_FAILURE);
}
value=get_semvalue();
printf("parent: the current value is %d\n", value);
printf("parent: will remove the sem\n");
if(semctl(sem_id, 0, IPC_RMID, (struct msquid_ds *)0) == -1){
perror("semclt");
exit(EXIT_FAILURE);
}
}
return 0;
}
static int set_semvalue(void)
{
union semun sem_union;
int value;
sem_union.val = 5;
if (semctl(sem_id, 0, SETVAL, sem_union) == -1) return(0);
printf("set value success,");
printf("init value is %d\n",get_semvalue());
return(1);
}
static int set_semvalue(void)
{
union semun sem_union;
int value = 5;
sem_union.val = value;
if((semctl(sem_id, 0, SETVAL, sem_union)) == -1){ // set value 5
return 0;
}
printf("set value success\n");
printf("init value is %d\n", get_semvalue());
return 1;
}
/************************************************************
* function: create or open the shared memory.
* iscreated: 1, to create the shm; 0, only to open the shm.
* mqsize: the count of the items
* itemsize: the size of an item (bytes)
* return: 0, correct; others, error number.
***********************************************************/
int shmmq_open(int iscreated, int mqsize, int itemsize)
{
int nflag;
int ret = 0;
/* Initial semaphore */
g_s_semid = get_semvalue((key_t)SEM_KEY);
if (-1 == g_s_semid) {
return ERROR_GET_SEMVALUE;
}
if (iscreated && -1 == set_semvalue(g_s_semid)) {
return ERROR_SET_SEMVALUE;
}
if (-1 == semaphore_p(g_s_semid)) {
return ERROR_SEMAPHORE_P;
}
while (1)
{
if (iscreated) {
nflag = 0666 | IPC_CREAT;
} else {
nflag = 0666;
}
g_s_mqsize = (mqsize <= 0) ? DEFAULT_MQ_SIZE : mqsize;
g_s_itemsize = (itemsize <= 0) ? DEFAULT_ITEM_SIZE : itemsize;
/* Initial shared memory */
g_s_shmid = shmget((key_t)SHM_KEY,
g_s_mqsize * g_s_itemsize + DEFAULT_HEAD_SIZE,
nflag);
if (-1 == g_s_shmid) {
ret = ERROR_SHMGET;
break;
}
g_s_pbase = shmat(g_s_shmid, NULL, 0);
if ((void *)-1 == g_s_pbase) {
g_s_pbase = NULL;
ret = ERROR_SHMAT;
break;
}
g_s_phead = (shmmq_head*)g_s_pbase;
g_s_pcontent = g_s_pbase + DEFAULT_HEAD_SIZE;
/* Initial head of the shared memory */
if (iscreated) {
g_s_phead->enq_pos = -1;
g_s_phead->deq_pos = -1;
}
break;
}
if (ret && iscreated) {
if (g_s_shmid >= 0) shmctl(g_s_shmid, IPC_RMID, 0);
semaphore_v(g_s_semid);
del_semvalue(g_s_semid);
return ret;
}
if (-1 == semaphore_v(g_s_semid)) {
return ERROR_SEMAPHORE_V;
}
return ret;
}