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Advanced Programming in the UNIX® Environment, Third Edition by Stephen A. Rago, W. Richard Stevens

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10. Signals

10.1. Introduction

Signals are software interrupts. Most nontrivial application programs need to deal with signals. Signals provide a way of handling asynchronous events—for example, a user at a terminal typing the interrupt key to stop a program or the next program in a pipeline terminating prematurely.

Signals have been provided since the early versions of the UNIX System, but the signal model provided with systems such as Version 7 was not reliable. Signals could get lost, and it was difficult for a process to turn off selected signals when executing critical regions of code. Both 4.3BSD and SVR3 made changes to the signal model, adding what are called reliable signals. But the changes made by Berkeley and AT&T were incompatible. ...

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