Inter Process Communication (IPC)

Programs running on a machine must be able to communicate with each other for any large and useful program. Since UNIX compartmentalizes each running program into its own process, all communication between processes (aptly called Interprocess Communication, or IPC) must go through the operating system. The operating system provides several methods of IPC, all offering their own advantages and disadvantages. A major design decision in any major software project is which type of interprocess communication to use.

The pages in this section go into several major types of interprocess communication, all of which are used somewhere in Runtime. To not repeat content, a summary will not be written here; please read the actual pages for an in-depth look at what each IPC method is and how to use it.

However, we will provide a chart here illustrating some of the key differences between the various IPC methods:

	Bidirectional	Processes Must Have Parent-Child Relationship	Can Have Multiple Readers/Writers
Pipes	No	No	No
FIFO	No	No	No
Serial	Yes	No	No
Shared Memory	Yes	No	Yes
Signals	No	No	N/A
Sockets (TCP)	Yes	No	No
Sockets (UDP)	Yes	No	Yes
Sockets (Unix; Streams)	Yes	No	No
Sockets (Unix; Datagrams)	Yes	No	Yes

(continued)

	Reliable	Connection-Oriented	Use Over Network	Use Over USB	Use Within Same Machine	Has Name on File System
Pipes	Yes	Yes	No	No	Yes	No
FIFOs	Yes	No	No	No	Yes	Yes
Serial	No	No	No	Yes	No	Yes
Shared Memory	N/A	N/A	No	No	Yes	Yes (on Linux)
Signals	Yes	N/A	No	No	Yes	No
Sockets (TCP)	Yes	Yes	Yes	No	Yes (using 127.0.0.1)	No
Sockets (UDP)	No	No	Yes	No	Yes (using 127.0.0.1)	No
Sockets (Unix; Streams)	Yes	Yes	No	No	Yes	Yes
Sockets (Unix; Datagrams)	Yes	No	No	No	Yes	Yes