RunLoop.swift

import UIKit
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

class ObjcClass: NSObject {
  
  func thisMethodWillBeEnqueuedToRunLoop() {
    print("I am executed")
  }
  
}

print("I am on \(Thread.current)")
print(1)

ObjcClass().performSelector(onMainThread: #selector(ObjcClass.thisMethodWillBeEnqueuedToRunLoop), with: nil, waitUntilDone: false)

print(2)
sleep(1)