Signals

Generic Cross Platform Signal Handler.

Prerequisites

Swift

• Swift Open Source swift-5.1-RELEASE toolchain (Minimum REQUIRED for latest release)
• Swift Open Source swift-5.4-RELEASE toolchain (Recommended)
• Swift toolchain included in Xcode Version 11.0 or higher.

BlueSignals version 2.0 and above supports Swift 5.1+. See older versions of BlueSSLService for older versions of Swift.

macOS

• macOS 10.14.6 (Mojave) or higher.
• Xcode Version 11.0 or higher using one of the above toolchains.
• Xcode Version 12.5 or higher using the included toolchain (Recommended).

iOS

• iOS 10.0 or higher
• Xcode Version 11.0 or higher using one of the above toolchains.
• Xcode Version 12.5 or higher using the included toolchain (Recommended).

Linux

• Ubuntu 16.04 (or 16.10 but only tested on 16.04) and 18.04.
• 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

Including in your project

Swift Package Manager

To include BlueSignals into a Swift Package Manager package, add it to the dependencies attribute defined in your Package.swift file. You can select the version using the majorVersion and minor parameters. For example:

    dependencies: [
        .Package(url: "https://github.com/Kitura/BlueSignals.git", majorVersion: <majorVersion>, minor: <minor>)
    ]

Carthage

To include BlueSignals in a project using Carthage, add a line to your Cartfile with the GitHub organization and project names and version. For example:

    github "Kitura/BlueSignals" ~> <majorVersion>.<minor>

CocoaPods

To include BlueSignals in a project using CocoaPods, you just add BlueSignals to your Podfile, for example:

    platform :ios, '10.0'

    target 'MyApp' do
        use_frameworks!
        pod 'BlueSignals'
    end

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.

Watching a signal

SignalWatch provides an interface that allows a trapped signal to notify multiple “signal watchers”. In this way, signal traps can be shared across libraries in the same application. In most cases this can be used as a direct replacement for trap().

When a signal is added via SignalWatch, it will install it’s own handler on that signal via trap(). As such, it is important to not use trap() directly when using SignalWatch. If all watchers of a signal are removed, SignalWatch will intelligently restore the handler that was installed before SignalWatch.

import Signals

...
let server: SomeServer = ...


SignalWatch.shared.on(signal: .int) { _ in
         server.shutdownServer()
}

server.run()

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

Community

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License

This library is licensed under Apache 2.0. Full license text is available in LICENSE.