main.swift

import Foundation
import Playground

private let lock = DispatchSemaphore(value: 1)
private let queue = DispatchQueue(label: "worker", attributes: .concurrent)
private let nWorkers = 5
private let stopAt = 1 << 30

private var i = 33550336
private var running = nWorkers

func calculatePerfect() {
  queue.async {
    lock.wait()

    let n = i

    i += 1

    guard n < stopAt else {
      running -= 1

      if running == 0 {
        exit(0)
      }

      lock.signal()
      return
    }

    lock.signal()

    if n.isMultiple(of: 100_000) {
      print("Passing \(n)")
    }

    if n.isPerfectNumber {
      print("\(n) is perfect")
    }

    calculatePerfect()
  }
}

for _ in 0..<nWorkers {
  calculatePerfect()
}

dispatchMain()