Multiple Workers in Swift Command Line Tool

Multiple workers in Swift Command Line Tool

I mistakenly interpreted the locking thread for a hanging program. The work will execute just fine without a run loop. The code in the question will run fine, and blocking the main thread until the whole group has finished.

So say chunks contains 4 items of workload, the following code spins up 4 concurrent workers, and then waits for all of the workers to finish:

let group = DispatchGroup()
let queue = DispatchQueue(label: "", attributes: .concurrent)

for chunk in chunk {
    queue.async(group: group, execute: DispatchWorkItem() {
        do_work(chunk)
    })
}

_ = group.wait(timeout: .distantFuture)

Swift or Objective-C command line tool and text to speech not outputting audio

NSSpeechSynthesizer.isAnyApplicationSpeaking() waits until the speech is finished.

import Foundation
import AppKit

class Speaker: NSObject , NSSpeechSynthesizerDelegate {
    var synth : NSSpeechSynthesizer!

    func run() {
        self.synth = NSSpeechSynthesizer.init()
        self.synth.delegate = self
        self.synth.startSpeakingString("First word")
        while(NSSpeechSynthesizer.isAnyApplicationSpeaking() == true) {}
    }
}

var speak : Speaker = Speaker.init()
speak.run()

Using NSURLSession from a Swift command line program

You can use a semaphore to block the current thread and wait for your URL session to finish.

Create the semaphore, kick off your URL session, then wait on the semaphore. From your URL session completion callback, signal the semaphore.

You could use a global flag (declare a volatile boolean variable) and poll that from a while loop, but that is less optimal. For one thing, you're burning CPU cycles unnecessarily.

Here's a quick example I did using a playground:

import Foundation

var sema = DispatchSemaphore( value: 0 )

class Delegate : NSObject, URLSessionDataDelegate
{
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data)
    {
        print("got data \(String(data: data, encoding: .utf8 ) ?? "<empty>")");
        sema.signal()
    }
}

let config = URLSessionConfiguration.default
let session = URLSession(configuration: config, delegate: Delegate(), delegateQueue: nil )

guard let url = URL( string:"http://apple.com" ) else { fatalError("Could not create URL object") }

session.dataTask( with: url ).resume()    

sema.wait()

How do you access command line arguments in Swift?

Apple has released the ArgumentParser library for doing just this:

We’re delighted to announce ArgumentParser, a new open-source library that makes it straightforward — even enjoyable! — to parse command-line arguments in Swift.

https://swift.org/blog/argument-parser/

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Swift Argument Parser

https://github.com/apple/swift-argument-parser

Begin by declaring a type that defines the information you need to collect from the command line. Decorate each stored property with one of ArgumentParser's property wrappers, and declare conformance to ParsableCommand.

The ArgumentParser library parses the command-line arguments, instantiates your command type, and then either executes your custom run() method or exits with useful a message.

Waiting for asynchronous calls in a swift script

Thanks to Aaron Brager, who linked to
Multiple workers in Swift Command Line Tool ,

which is what I used to find my answer, using dispatch_groups to solve the problem.

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