dan-rodrigues / swift-simple-queue-playground

Swift 5.0 playground implementing a minimal DispatchQueue equivalent

Swift SimpleQueue Playground

This repo is a personal project and doesn't contain anything intended for use in a production setting.

Background

This is a Swift 5.0 playground that serves as a scratchpad for implementing a minimal equivalent of DispatchQueue using only the condition classes provided by Foundation. Only NSThread, NSCondition and NSConditionLock are used which provides enough functionality to suspend and resume threads only when needed.

API

The implementation is called SimpleQueue and is modelled after DispatchQueue. Since this is a minimal demo project, most of the functionality DispatchQueue offers beyond async() / sync() isn't provided. The equivalent of a concurrent queue is configured by configuring SimpleQueue with a workerCount greater than 1.

The "unchecked rethrows" trick used by DispatchQueue to circumvent the compiler isn't used here, since it apparently exploits a compiler bug. withoutActuallyEscaping() is used to to implement SimpleQueue.sync().

final class SimpleQueue {

    init(workerCount: Int)

    func async(_ work: @escaping () -> Void)

    @discardableResult
    func sync<Result>(_ work: () -> Result) -> Result
}

TODO

• A better set tests

Tools

Xcode 12.5.1 was used to create the playground.