Shared memory provides an efficient way for multiple processes to share data (for example, control information that all processes require access to). Commonly, the processes use semaphores to take turns getting access to the shared memory. For example, a server process can use a semaphore to lock a shared memory area, then update the area with new control information, use a semaphore to unlock the shared memory area, and then notify sharing processes. Each client process sharing the information can then use a semaphore to lock the area, read it, and then unlock it again for access by other sharing processes.
Processes can also use shared mutexes and shared read-write locks to communicate. For more information on mutexes and read-write locks see Synchronization primitives.