11.21 Interprocess communication functions Process ID 55 Program A Process ID 70 Program B Process ID 92 Program C Kernel Data Space Figure 11-26 Interprocess communication functions Interprocess communications Support for XPG4 introduced Interprocess Communication (IPC) functions in z/OS UNIX. These IPC functions were required by many applications, particularly client/server applications. Message queues - Message queues allow a client and a server process to communicate through one or more message queues in the kernel. A process can create, read from, or write to a message queue. Multiple client and server processes can share the same queue. Shared memory - Shared memory provides a method of sharing data in storage between multiple processes. The shared data is kept in a data space created by the kernel. The data can be shared between a parent and child process or between unrelated processes. Semaphores - Semaphores are used for serializing access to shared memory. A program using shared memory must get a semaphore before it allocates shared memory. Chapter 11. z/OS UNIX PARMLIB members 631