15.11. Summary

We've detailed numerous forms of interprocess communication: pipes, named pipes (FIFOs), and the three forms of IPC commonly called XSI IPC (message queues, semaphores, and shared memory). Semaphores are really a synchronization primitive, not true IPC, and are often used to synchronize access to a shared resource, such as a shared memory segment. With pipes, we looked at the implementation of the popen function, at coprocesses, and the pitfalls that can be encountered with the standard I/O library's buffering.

After comparing the timing of message queues versus full-duplex pipes, and semaphores versus record locking, we can make the following recommendations: learn pipes and FIFOs, since these two basic techniques can still be used effectively in numerous applications. Avoid using message queues and semaphores in any new applications. Full-duplex pipes and record locking should be considered instead, as they are far simpler. Shared memory still has its use, although the same functionality can be provided through the use of the mmap function (Section 14.9).

In the next chapter, we will look at network IPC, which can allow processes to communicate across machine boundaries.