#include
#include
#include
#define SEM_PATH "/unix/my_sem"
#define max_tries 3
int semid.
main()
{
int flag1,flag2,key,i,init_ok,tmperrno.
struct semid_ds sem_info.
struct seminfo sem_info2.
union semun arg. //union semun： 请参考附录2
struct sembuf askfor_res, free_res.
flag1=IPC_CREAT|IPC_EXCL|00666.
flag2=IPC_CREAT|00666.
key=ftok(SEM_PATH, a ).
//error handling for ftok here.
init_ok=0.
semid=semget(key,1,flag1).//create a semaphore set that only includes one semphore.
if(semidsem_otime!=0){ i=max_tries. init_ok=1.}
else sleep(1).
}
}
if(!init_ok)
// do some initializing, here we assume that the first process that creates the sem will
// finish initialize the sem and run semop in max_tries*1 seconds. else it will not run
// semop any more.
{
arg.val=1.
if(semctl(semid,0,SETVAL,arg)==-1) perror("semctl setval error").
}
}
else
{perror("semget error, process exit"). exit(). }
}
else //semid>=0. do some initializing
{
arg.val=1.
if(semctl(semid,0,SETVAL,arg)==-1)
perror("semctl setval error").
}
//get some information about the semaphore and the limit of semaphore in redhat8.0
arg.buf=&.sem_info.
if(semctl(semid, 0, IPC_STAT, arg)==-1)
perror("semctl IPC STAT").
printf("owner s uid is %d\n", arg.buf->sem_perm.uid).
printf("owner s gid is %d\n", arg.buf->sem_perm.gid).
printf("creater s uid is %d\n", arg.buf->sem_perm.cuid).
printf("creater s gid is %d\n", arg.buf->sem_perm.cgid).
arg.__buf=&.sem_info2.
if(semctl(semid,0,IPC_INFO,arg)==-1)
perror("semctl IPC_INFO").
printf("the number of entries in semaphore map is %d \n", arg.__buf->semmap).
printf("max number of semaphore identifiers is %d \n", arg.__buf->semmni).
printf("mas number of semaphores in system is %d \n", arg.__buf->semmns).
printf("the number of undo structures system wide is %d \n", arg.__buf->semmnu).
printf("max number of semaphores per semid is %d \n", arg.__buf->semmsl).
printf("max number of ops per semop call is %d \n", arg.__buf->semopm).
printf("max number of undo entries per process is %d \n", arg.__buf->semume).
printf("the sizeof of struct sem_undo is %d \n", arg.__buf->semusz).
printf("the maximum semaphore value is %d \n", arg.__buf->semvmx).
//now ask for available resource:
askfor_res.sem_num=0.
askfor_res.sem_op=-1.
askfor_res.sem_flg=SEM_UNDO.
if(semop(semid,&.askfor_res,1)==-1)//ask for resource
perror("semop error").
sleep(3). //do some handling on the sharing resource here, just sleep on it 3 seconds
printf("now free the resource\n").
//now free resource
free_res.sem_num=0.
free_res.sem_op=1.
free_res.sem_flg=SEM_UNDO.
if(semop(semid,&.free_res,1)==-1)//free the resource.
if(errno==EIDRM)
printf("the semaphore set was removed\n").
//you can comment out the codes below to compile a different version:
if(semctl(semid, 0, IPC_RMID)==-1)
perror("semctl IPC_RMID").
else printf("remove sem ok\n").
} |
