Interprocess communication in the ninth edition unix system

Abstract

When processes wish to communicate, they must first establish communication. The stream mechanisms introduced in the Eighth Edition Unix system,1 which have now become part of AT&T's Unix System V2, provide a flexible way for processes to conduct an already‐begun conversation with devices and with each other: an existing stream connection is named by a file descriptor, and the usual read, write, and I/O control requests apply. Processing modules may be inserted dynamically into a stream connection, so network protocols, terminal processing, and device drivers separate cleanly. However, these mechanisms, by themselves, do not provide a general way to create channels between processes. Simple extensions provide new ways of establishing communication. In our system, the traditional Unix IPC mechanism, the pipe, is a cross‐connected stream. A generalisation of file‐system mounting associates a stream with a named file. When the file is opened, operations on the file are operations on the stream. Open files may be passed from one process to another over a pipe. These low‐level mechanisms allow construction of flexible and general routines for connecting local and remote processes.

Inverting X: an architecture for a shared distributed window system

“…XPEI, supports the XPEA architecture and dramatically simplifies the implementation of XPSes by enabling the programmer to work at a higher level of abstraction and by encouraging code reuse. [18]. The task of implementing a particular window system capability can be broken down into component tasks performed by small filters.…”

“…Three of these are the z-Kernel [8], Packet Filters [14], and Eighth Edition Unix Streams [18]. (For a detailed comparison of XPEL and these systems, see [la].)…”