There are wo source files aa.c and bb.c. In the aa.c, I create a shared memory and do the fork. I do the exe() in the child after fork to the bb.c file. I also increment the count in the aa.c file.

I only can read data from shared memory in bb.c file, but I need to output some data when the count are 20 and 40. It means I have to constantly check the data in shared memory.

How can I make it happen by using a semaphore? Could you please write a code to explain it?

Thank you in advance!