CODEWITHSUNDEEP
csemaphore
Abhishek Tiwari
Abhishek Tiwari

Reputation: 35

How to use semctl to set value of nth semaphore in the semaphore set

I have created a System V semaphore using semget

#define SEM_ID 250
...
sem_set_id = semget(SEM_ID, 1, IPC_CREAT | 0660);
if (sem_set_id == -1) {
perror("main: semget");
exit(1);

now as per my understanding this creates a semaphore set which has many semaphores in it. But how to identify a particular semaphore to set its value using semctl...

int iter=0;
for(iter=0;iter<no_of_jobs;iter++)
{
    int rc=semctl(semid,iter,SETVAL, sem_val);
    if(rc==-1)
        {printf("Error:semctl\n");
        exit(1);
        }
}

The above code runs for iter=0 but fails for other. In struct semun sem_val I have set the value sem_val.val=1;

Upvotes: 1

Views: 1834

Answers (1)

Jonathan Leffler
Jonathan Leffler

Reputation: 753695

The second argument to semget() is the number of semaphores in the semaphore set. You specified 1, so you got one semaphore. Accessing anything other than the one semaphore is going to lead to errors.

Change the 1 to 10, say, and you should be OK to iterate over semaphores 0..9 inclusive.

Upvotes: 2

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