Linux Shared Memory Synchronization

Question

I have implemented two applications that share data using the POSIX shared memory API (i.e. shm_open). One process updates data stored in the shared memory segment

Answer 1

If efficiency is important, I would go with process-shared mutexes and condition variables.

AFAIR, each operation with a semaphore requires a syscall, so uncontended mutex should be faster than the semaphore [ab]used in mutex-like manner.