Signals

Overview

Generic Cross Platform Signal Handler.

Prerequisites

Swift

Swift Open Source swift-4.0.0-RELEASE toolchain (Minimum REQUIRED for latest release)
Swift Open Source swift-4.1.2-RELEASE toolchain (Recommended)
Swift toolchain included in Xcode Version 9.4 or higher.

macOS

macOS 10.11.6 (El Capitan) or higher.
Xcode Version 9.0 or higher using one of the above toolchains.
Xcode Version 9.4 or higher using the included toolchain (Recommended).

iOS

iOS 10.0 or higher
Xcode Version 9.0 or higher using one of the above toolchains.
Xcode Version 9.4 or higher using the included toolchain (Recommended).

Linux

Ubuntu 16.04 (or 16.10 but only tested on 16.04).
One of the Swift Open Source toolchain listed above.

Build

To build Signals from the command line:

% cd <path-to-clone>
% swift build

Using Signals

Before starting

The first thing you need to do is import the Signals framework. This is done by the following:

import Signals

Provided APIs

Signals provides four (4) class level APIs. Three (3) are used for trapping and handling operating system signals. The other function allows for the raising of a signal.

Trapping a signal

trap(signal signal: Signal, action: SigActionHandler) - This basic API allows you to set and specific handler for a specific signal.

The example below shows how to add a trap handler to a server in order to perform and orderly shutdown in the event that user press ^C which sends the process a SIGINT.

import Signals

...

let server: SomeServer = ...

Signals.trap(signal: .int) { signal in

	server.shutdownServer()
}

server.run()

Additionally, convenience API's that build on the basic API specified above are provided that will allow for trapping multiple signals, each to a separate handler or to a single handler.

trap(signals signals: [(signal: Signal, action: SigActionHandler)]) - This lets you trap multiple signals to separate handlers in a single function call.
trap(signals signals: [Signal], action: SigActionHandler) - This API lets you trap multiple signals to a common handler.

Raising a signal

raise(signal signal: Signal) - This API is used to send an operating system signal to your application.

This example illustrates how to use Signals to raise a signal with the OS, in this case SIGABRT.

import Signals

...

Signals.raise(signal: .abrt)

Ignoring a signal

func ignore(signal: Signal) - This API is used to ignore an operating system signal.

This example illustrates how to use Signals to ignore a signal with the OS, in this case SIGPIPE.

import Signals

...

Signals.ignore(signal: .pipe)

Restoring a signals default handler

func restore(signal: Signal) - This API is used to restore an operating system signals default handler.

This example illustrates how to use Signals to restore a signals default handler, in this case SIGPIPE.

import Signals

...

Signals.restore(signal: .pipe)

Adding a USER-DEFINED signal

This example shows how to add a user defined signal, add a trap handler for it and then raise the signal.

import Signals

let mySignal = Signals.Signal.user(20)

Signals.trap(signal: mySignal) { signal in

	print("Received signal \(signal)")
}

Signals.raise(signal: mySignal)

The output of the above snippet is:

Received signal 20

helenmasters/BlueSignals