Code for https://alexdremov.me/using-threads-in-swift/

file1.swift

class MyThread: Thread {
    override func main() { // Thread's starting point
        print("Hi from thread")
    }
}

let thread = MyThread()
thread.start()

file2.swift

class MyThread: Thread {
    let waiter = DispatchGroup()

    override func start() {
        waiter.enter()
        super.start()
    }

    override func main() {
        task()
        waiter.leave()
    }

    func task() {
        print("Hi from thread")
    }

    func join() {
        waiter.wait()
    }
}

let thread = MyThread()
thread.start()

thread.join() // Waits for thread completion

file3.swift

class MyThread: Thread {
    ...
	func exit() {
        waiter.leave()
        Thread.exit()
    }
    ...
}

file4.swift

class MyThread: Thread {
	let waiter = DispatchGroup()

	override func start() {
		waiter.enter()
		super.start()
	}

	override func main() {
		task()
		waiter.leave()
	}

	func exit() {
		waiter.leave()
		Thread.exit()
	}

	func task() {
		let start = Date.now
		for _ in 0...100500 {
			if isCancelled {
				let seconds = Double(Date.now.timeIntervalSince(start))
				print("Cancelled after \(seconds) seconds")
				exit()
			}
			Thread.sleep(forTimeInterval: 0.01) // Long task
		}
	}

	func join() {
		waiter.wait()
	}
}

let thread = MyThread()
DispatchQueue.global().asyncAfter(
	deadline: .now().advanced(by: .seconds(5))) {
	thread.cancel()
}
thread.start()
thread.join()