How do I detect if there are multiple windows of my game open?

Help
1

Godot Version

4.6.3.stable

Question

I’ve seen multiple games where if you open another window of the game when you already have one open, it gives you a message saying you can’t have multiple open, and then that second one closes. How do I achieve this? Or in short: How do I detect if there are multiple windows of my game open?

There are multiple games that I’ve made that would benefit from having this implemented. So thanks in advanced!

2

There’s no built-in way to do this, but I’ll give you an answer I gave another user:

3

Every project gets its own per-user persistent storage that scripts can acces using user://-prefixed URLs.
Notice how i said “every project”, not “every instance”. Never tried it myself, but i think two instances of the same project will share the same user:// base directory.
Knowing this, you can keep a resource at user://instances.tres and have the game load it at startup.


class GameInstances extends Resource:
  @export var instances: Array[GameInstanceEntry]
  pass

class GameInstanceEntry extends Resource:
  @export var pid: int
  @export var name: String

  func _init(new_pid, new_name):
    pid = new_pid
    name = new_name
    pass
  pass

Then at game start you make some script check for entries on that resource:

var game_instances = load("user://instances.tres")
if (not game_instances.is_empty()):
  # there is already an instance running
  # bunch of cross-window multiplayer code...
  pass
else:
  # there are no other instances running.
  # single-player init...
  pass
  game_instances.append(GameInstanceEntry.new(OS.get_process_id(), "MY GAME 3: RELOADED RETURNS PLUS ULTRA TURBO"))
  # you can order players by instance spawn order
  set_player_id(game_instances.length())
  game
4

Based on the posts text, I think OP isn’t looking for a local multiplayer game, and instead, wants to make sure only a single instance of their game runs.

In that case, your code has a flaw which the answer I gave above fixes:
If your game crashes, the residual file will still exist, and at that point, your game can no longer function until your player manually removes the file.

5

If pid file is used, you could check if the process with given pid still exists, but I guess that would require executing OS specific stuff with OS.execute.

6

Another way would be creating TCP server. Something like this:

var server: TCPServer

func _ready() -> void:
	server = TCPServer.new()
	var ok = server.listen(12345, "127.0.0.1")
	if ok != OK:
		prints("probably already running another instance")

But this isn’t problem free either. You need to pick a port number than nobody else uses. Unfortunately the port number is only a 16 bit integer, so it is pretty much guaranteed that someone has something else already running on that port.

7

I could include crash handling and live instance introspection but then a bunch of other stuff would have be be cascaded into the example and the small suggestion would turn into a 400-line cross-instance bus.