How to handle a blocking task(fswatch)?

[jiyinyiyong]

I don't have much experience on blocking programs yet...

Based on <https://github.com/paul-nameless/nim-fswatch>
    
    
    import libfswatch
    import libfswatch/fswatch
    
    proc callback(event: fsw_cevent, event_num: cuint) =
      echo event.path
    
    var mon = newMonitor()
    
    mon.addPath("/tmp/test/")
    mon.setCallback(callback)
    
    mon.start()
    
    
    Run

and `mon.start()` is blocking.

Meanwhile I want to launch a window, which also wants to block my program using 
a `while true` loop.

Now the problem is `mon.start()` has blocked the problem, how can I respond to 
window as well?

Tried to put window in a thread. Since I was using sdl2, sdl2 threw an error 
that it has to be running in a main thread. Then I saw people using `spawn` for 
tasks, but as I tried, the compiler told me that `mon.setCallback` is not GC 
safe. Got no other solutions to try...