Ruby thread.join does not return when using curses gem

Question

I'm trying to get the ruby curses gem to run with multiple threads (on Windows) to run a serial port:

require 'serialport'
require 'curses'
include Curses

init_screen
start_color
curs_set(0)
noecho

$cont = true

uartThread = Thread.new do
  baudRate  = 115200
  portNo    = 17

  begin
    $port = SerialPort.new(portNo, baudRate, 8, 1, SerialPort::NONE)
  rescue
    puts "Could not open serial port"
  end

  while $cont == true
    puts $cont
    sleep(1)
  end 

  puts "End of thread"
end



begin
  $win = Curses::Window.new(0,0,1,2)

  refresh

  while $cont 
    key = getch.to_s

    case key 
    when '5'
      $cont = false
    end 

    refresh
  end
ensure
  close_screen
  puts "ensured!"
end 

puts "Before join"
uartThread.join
puts "After join"

It basically all works fine (this is just the MRE), I just cant get the program to exit properly: Hitting "5" will stop the curses loop execution but the uartThread.join never returns and to console window I ran the program in, becomes unresponsive (to Ctrl+C etc.) and I can only close the entire window. This isn't a huge problem, just incredibly annoying.

The output looks like this:

true
true
true
ensured!
Before join

I know the global variable solution to stop thread execution isn't pretty, but it's just a test script and fine for now. The same thing works perfectly fine if I exclude the curses part and running curses and the serial port thread also works fine, it's just closing the uartThread gracefully that doesn't work. I tried killing the thread or running join(0) to immediately return and just taking out the loop from the uartThread, somehow curses won't allow that thread to run to completion and I have no idea why?

Running ruby 3.1.3p185 in a git bash console (same behavior in the win cmd prompt) on a Win10 machine.

Edit: I did mess around a bit more and found out a bit more.

1. When using curses, the global variable $cont only gets written in the main thread not in the uartThread and so the thread doesn't terminate. However this does work when not using curses.

2. I cant kill other threads when running curses:

   puts uartThread.status

   uartThread.exit

   puts uartThread.status

Will print run or sleep both times (again this works without curses).

So I'm guessing I need to somehow make this work singlethreaded...