I have this code:

    let timer1 = Timer(timeInterval: 1, repeats: true) { _ in
      print("FOO1")
    }
    let timer2 = Timer(timeInterval: 1, repeats: true) { _ in
      print("FOO2")
    }
    let timer3 = Timer(timeInterval: 1, repeats: true) { _ in
      print("FOO3")
    }
    
    let queue = DispatchQueue(label: "")
    queue.async {
      RunLoop.current.add(timer1, forMode: .common)
      RunLoop.current.run()
    }
    queue.async {
      RunLoop.current.add(timer2, forMode: .common)
    }
    queue.async {
      RunLoop.current.add(timer3, forMode: .common)
    }

In the current code, only timer1 is run. This is strange, because timer2 and timer3 are added to a running runloop. I recall in the main run loop (which is already running so I don’t have to call run again), I can simply add timers I want to add, and the timers will get triggered no problem.

My findings:

• If I move RunLoop.current.run() to the last async block, then all timers will be run.
• If I add RunLoop.current.run() to all the 3 async blocks, only timer1 is run.
• Changing .common to .default mode won’t help

I am wondering why is my runloop behaving differently than the main runloop, and how can i mimic the behavior of main runloop?