Mastering Linux Kernel Development

System V message queues

This is the classic AT&T message queue implementation suitable for messaging between an arbitrary number of unrelated processes. Sender processes wrap each message into a packet containing message data and a message number. The message queue implementation does not define the meaning of the message number, and it is left to the application designers to define appropriate meanings for message numbers and program readers and writers to interpret the same. This mechanism provides flexibility for programmers to use message numbers as message IDs or receiver IDs. It enables reader processes to selectively read messages that match specific IDs. However, messages with the same ID are always read in FIFO order (first in, first ...