How does X Server assign Window ID?

[Sheng Yu]

Hi all,

I have been tracking for a bug that makes my program crashing when
calling function glXMakeCurrent.
My program runs with multi-displays, ':0.0', ':1.0', ':1.1', ':2.0',
':2.1'. When glXMakeCurrent() is called
to switch rendering context from ':0.0' to either ':1.0', ':1.1' or
':2.0', ':2.1', the program runs fine.
However, if the rendering context is switch from ':1.1' to ':2.0',
the program crashes with with a
segmentation fault.

The interesting thing  I found when debugging is the window ID and
root window ID for each display:
display:':0.0',screen: 0, root window id: 315, window id: 71303171
display:':1.0',screen: 0, root window id: 595, window id: 2097156
display:':1.1',screen: 1, root window id: 597, window id: 4194308
display:':2.0',screen: 0, root window id: 595, window id: 2097156
display:':2.1',screen: 1, root window id: 597, window id: 4194308

It seems that X Server 1 and 2 assign window ID with the same
strategy, which is different from X Server 0.
I am wondering whether it is causing the crashing, which indicates
problems in X Server settings. I have
been digging into the source of X Server and I cannot find how the
window ID is assigned. Could someone
tell me which file I should look into? Thanks a lot!

Suggestions about how to debug this problem are also greatly appreciated!

Yu Sheng