Anyone got an idea how to get from an Xserver the list of all open windows?
From the CLI you can use
xwininfo -tree -root
If you need to do this within your own code then you need to use the XQueryTree function from the Xlib library.
You can also take a look at the _NET_CLIENT_LIST value of the root window. This is set by most modern window managers:
xprop -root|grep ^_NET_CLIENT_LIST
That value can easily be obtained programmatically, see your Xlib documentation!
来源：https://stackoverflow.com/questions/252906/how-to-get-the-list-of-open-windows-from-xserver