Re: [GD-Windows] Limiting to one instance

[Stefan B. <Ste...@di...>]

   But you don't need a global mutex, just a named session mutex, no? =
I.e. just a plain named Mutex (without \\global\ prefix) will do if you =
want the mutex to apply only to the current user session.

/Stefan

> -----Original Message-----
> From: gam...@li...
> [mailto:gam...@li...] On Behalf =
Of
> Dirk Ringe
> Sent: 15 August 2006 10:22
> To: Alen Ladavac; Game Development for MS Windows; Andrew Grant
> Subject: Re: [GD-Windows] Limiting to one instance
>=20
> One thing to keep in mind when using global objects in windows is Fast
> User Switching in Windows XP, where in fact multiple users are logged =
in
> at the same time. When you use CreateMutex you block the application =
from
> running under ALL other user accounts as well. This could as well =
apply to
> FindWindow. If you do not want this to happen, you have to use a =
technique
> which is per user, like the old unix style pid file stored under the =
users
> home directory.
>=20
> Dirk
>=20
> -----Urspr=FCngliche Nachricht-----
> Von: gam...@li...
> [mailto:gam...@li...] Im Auftrag =
von
> Alen Ladavac
> Gesendet: Dienstag, 15. August 2006 10:13
> An: Andrew Grant
> Cc: Game Development for MS Windows
> Betreff: Re: [GD-Windows] Limiting to one instance
>=20
> > I remember at an old company one genius tried to prevent multiple
> instances
> > of an app by binding a port, and was then surprised when it failed =
for
> > pretty much everyone who was running a firewall!
>=20
> Actually, it's not such a weird idea. Some applications rely on IP
> ports as a simple yet very portable IPC mechanism. Firewalls should
> really know better, by handling 127.0.0.1 specifically by default. But
> apparently even the best in class don't.
>=20
> Btw, in my book, even using a named mutex in that way is a bit hacky
> because you are relying on error. But what can we do, when there's no
> real API intended for that purpose.
>=20
> Personally, I've been using FindWindow(xyz, NULL) to find a main
> window by class name. Same principle (with same weaknesses as a named
> mutex), but doesn't require an extra object creation, as you probably
> already have a window, and you can use this to test even for foreign
> applications, because it doesn't require access to the code of the
> tested application. A nice side effect is that once you have the
> window, you can report messages like "Cannot start, please close ABCD
> application first", where you get the ABCD from the application's main
> window caption.
>=20
> Cheers,
> Alen
>=20
>=20
> =
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