[ clisp-Bugs-2002364 ] XID reuse causes clx cache to get out of sync

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Bugs item #2002364, was opened at 2008-06-25 06:38
Message generated for change (Comment added) made by sds
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Category: clx
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Shawn Betts (sabetts)
Assigned to: Bruno Haible (haible)
Summary: XID reuse causes clx cache to get out of sync

Initial Comment:
I've isolated a bug in clx that manifests itself in stumpwm as the
:window slot in some events coming in as a pixmap instead of a
window. The problem stems from X reusing XIDs for drawables (windows
and pixmaps) and clx's cache getting out of sync. Here is a function
that shows the problem:

(defun break-display-xid-cache ()
  (labels ((make-win (dpy)
             (xlib:create-window :parent (xlib:screen-root (first
                                                            (xlib:display-roots dpy))) :x 0 :y 0 :width 50 :height 50))
           (make-pixmap (window)
             (xlib:create-pixmap :width (random 100) :height (random
                                                              100) :depth 8 :drawable window))
           (first-pass (dpy)
             ;; Open a fresh connection. Create a window and a pixmap.
             (let* ((dpy2 (xlib:open-default-display))
                    (window (make-win dpy2))
                    (pixmap (make-pixmap window)))
               ;; make the pixmap the window's icon pixmap hint.
               (setf (xlib:wm-hints window) (xlib:make-wm-hints
                                             :icon-pixmap pixmap))
               (format t "Window ID: ~s pixmap ID: ~s~%"
                       (xlib:window-id window) (xlib:pixmap-id pixmap))
               (xlib:display-finish-output dpy2)
               ;; On the old connection, list the root window children
               ;; and the icon pixmap hint to cache their XIDs.
               (loop for w in (xlib:query-tree (xlib:screen-root
                                                (first (xlib:display-roots dpy))))
                  for hints = (xlib:wm-hints w)
                  when hints
                  do (format t "top level window id: ~s | icon pixmap hint: ~s~%" (xlib:window-id w) (xlib:wm-hints-icon-pixmap hints)))
               (xlib:close-display dpy2)))
           (second-pass (dpy)
             ;; Open a fresh connection and create 2 windows.
             (let* ((dpy2 (xlib:open-default-display))
                    (window1 (make-win dpy2))
                    (window2 (make-win dpy2)))
               (format t "Window#1 ID: ~s Window#2 ID: ~s~%"
                       (xlib:window-id window1) (xlib:window-id window2))
               (xlib:display-finish-output dpy2)
               ;; On the old connection, list the root window children
               ;; and note the second window is erroneously a pixmap
               ;; due to too agressive caching in clx.
               (loop for w in (xlib:query-tree (xlib:screen-root
                                                (first (xlib:display-roots dpy))))
                  do (format t "window: ~s~%" w))
               (xlib:close-display dpy2))))
    (let ((dpy (xlib:open-default-display)))
      (first-pass dpy)
      (second-pass dpy)
      (xlib:close-display dpy))))


Note that the last window in the window list is a pixmap! Here's the output I get:

[4]> (break-display-xid-cache)
Window ID: 20971521 pixmap ID: 20971522
top level window id: 20971521 | icon pixmap hint: #<XLIB:PIXMAP 60x88+0+0 localhost #x01400002 #x20426CAE>
Window#1 ID: 20971521 Window#2 ID: 20971522
window: #<XLIB:WINDOW 50x50+0+0 localhost #x01400001 #x20425C8E>
window: #<XLIB:PIXMAP 50x50+0+0 localhost #x01400002 #x20426CAE>
#<XLIB:DISPLAY XLIB:CLOSED-DISPLAY #x2042478E>
[5]> 

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>Comment By: Sam Steingold (sds)
Date: 2008-06-30 16:50

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when I modify your code to avoid having two connections open at the same
time, the problem disappears.
Shawn, are you sure your code is legit?

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Comment By: Sam Steingold (sds)
Date: 2008-06-26 09:56

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now that I fixed amd64 wm-hints, I see this on all platforms.
I think it would be a good idea to check if this is also observable on
other lisps and to discuss this on  gmane.lisp.clx.devel

----------------------------------------------------------------------

Comment By: Sam Steingold (sds)
Date: 2008-06-25 10:29

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are you sure that the whole notion of two dpy objects being open
simultaneously is valid?
I have a feeling that the X people would consider this to be a user
program bug.

----------------------------------------------------------------------

Comment By: Sam Steingold (sds)
Date: 2008-06-25 09:48

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confirm on both mit-clx and new-clx on i386,
but NOT on amd64

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