Share POSIX semaphore among multiple processes

Question

I need to create two child processes each of which calls its own execvp on fork and the executable share common POSIX semaphores between them.
So do I need to create a shared memory or just implement named semaphores?

Answer 1

I think you must create shared memory using shm_open(). Then create the semaphore for the shared memory.

When you are creating the semaphore, you are indicating whether the semaphore is shared between 2 threads or 2 processes.
with the help of the pshared variable. You should use pshared as a non-zero value to say it's an inter proecess semaphore.

int sem_init(sem_t *sem, int pshared, unsigned int value);

Please see :
http://man7.org/linux/man-pages/man3/sem_init.3.html
and
http://man7.org/linux/man-pages/man3/shm_open.3.html