C semaphores using sem_wait()

Question

I am working with semaphores and I am struggling with one part of code.
CODE:

// semaphore initialized to zero
for( int i = 0; i < N; i++ )
{
    fork();
    // statements
    sem_wait(semaphore);
    printf("Process %d is done\n", i);
    exit(0);
}

for( int i = 0; i < N; i++ )
{
    sem_post(semaphore);
}

Problem is, that loop stops after first iteration because of sem_wait, but i would like it to stop only that current process, so all other iterations can be done and at the end of code, i will 'release' all processes. Is there a way how to accomplish this?
Thank you!

EDIT:

// initialization of semaphore
semaphore = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
sem_init(semaphore, 1, 0);

Can you explain what you mean by the "current process"? Once you explain what you mean by that, just wrap the call to sem_wait in an if statement that tests whatever it is you need to test. — David Schwartz
– David Schwartz, Commented May 1, 2017 at 9:34
Well, in for loop i call fork() N times, so i create N processes. So current process i mean each process every iteration. — SevO
– SevO, Commented May 1, 2017 at 9:36
@SevO I don't follow. If the current process is each process every iteration, then what isn't the current process? — David Schwartz
– David Schwartz, Commented May 1, 2017 at 9:43
Let's say i=0 and first process is called. Code comes to part where semaphore is blocked. I want to accomplish that even process is blocked, loop continues, so one by one i create queue of processes and at the end i use sem_post() and release them. — SevO
– SevO, Commented May 1, 2017 at 9:48

Kamal Palei · Accepted Answer · 2017-05-01 09:41:37Z

1

Please check fork return value. On that basis, you will be sure if code is executed under child or parent process. Accordingly call sem_wait.

answered May 1, 2017 at 9:41

Kamal Palei

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