Re: Existence Announcement

[muppet <scott asofyet org>]

On Apr 5, 2005, at 9:52 PM, ADIS - C.P.D. wrote:

> How to identify a window to known whether it already exists?
> I want to prevent multiple instances of the same window.

is that multiple instances of the same window within the same process, 
or you want to prevent multiple processes?

within the same process is easy -- use Gtk2::Window::list_toplevels() 
to get a list of all the toplevel windows in your app, and search 
through that for a given window.


multiple processes will involve some form of IPC.  i've never done this 
with X, but for some reason i can never resist a challenge, so i poked 
around a bit in the mozilla sources to see how mozilla's remote 
commands work...  there's a remote-helper, a tiny program that links to 
Xlib.  this program uses XQueryTree() to fetch a list of all windows, 
then iterates through those windows, using XGetWindowProperty() to look 
for the first one that has certain Atoms set.  when it finds this 
window (which belongs to a running mozilla instance), it uses 
XChangeProperty() to change the value of the Atom on which mozilla will 
be listening for commands.  the X server sends an event to the owner of 
the window, which happens to be mozilla, who responds by parsing and 
executing the command.  at this point, the remote-helper is usually 
already gone.

gdk_property_get() and gdk_property_change(), the wrappers for 
XGetWindowProperty() and XChangeProperty(), are bound in gtk2-perl as 
Gtk2::Gdk::Window::property_get() and 
Gtk2::Gdk::Window::property_change(), respectively.

but gdk does not expose a direct wrapper for XQueryTree(), so there is 
no way to search all of the windows on the display for one with the 
desired property.  the X11::Protocol module on CPAN provides this 
functionality, or, if you already have some xs in your app, you could 
very easily create your own function to do this with Xlib.


on win32, WinMain gets the instance handle and previous instance 
handle, so you can decide whether to create a new window or message the 
old one.  i haven't looked into it, but i suspect the win32 port of 
gtk+ doesn't expose this either, and you'd have to use the Win32 
module.


i'm sure there are other ways, but i don't know off the top of my head.


--
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