The Linux Programming Interface

878 Chapter 43

Although some of these facilities are concerned with synchronization, the general

term interprocess communication (IPC) is often used to describe them all.

Figure 43-1: A taxonomy of UNIX IPC facilities

As Figure 43-1 illustrates, often several facilities provide similar IPC functionality.

There are a couple of reasons for this:

z Similar facilities evolved on different UNIX variants, and later came to be

ported to other UNIX systems. For example, FIFOs were developed on System V,

while (stream) sockets were developed on BSD.

z New facilities have been developed to address design deficiencies in similar

earlier facilities. For example, the POSIX IPC facilities (message queues, sema-

phores, and shared memory) were designed as an improvement on the older

System V IPC facilities.

communication

data

transfer

message

byte

stream

shared

memory

synchronization

semaphore

file lock

fcntl())

flock())

signal

pseudoterminal

anonymous

mapping