XDamageSubtract usage

[McDonald, Michael-p7438c]

I've been playing around with the Xdamage extension and I'm having a
hard time figuring out how XDamageSubtract should be used. When I
receive a XDamageNotify event, I "repair" the damaged area, and then I
tell the server that I've repaired it using XDamageSubtract. That all
works fine except when the monitored window is being destroyed. 

  When the window is destroyed, the Damage ID is invalidated. This
causes a race condition between the XDamageNotify event and the
DestroyNotify event. By the time my app receives the XDamageNotify
event, the Damage identifier is invalid. It seems like no amount of
peeking ahead at the events will eliminate this race condition.

  What is the recommended method for handling this race condition?

Mike McDonald
GDC4S/FCS/PVM/SDC