[Tcl-bugs] [ tktoolkit-Bugs-1789819 ] Panic in [wm stackorder]

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Bugs item #1789819, was opened at 2007-09-07 03:10
Message generated for change (Comment added) made by dkf
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Category: 67. Unix Window Operations
Group: None
Status: Open
Resolution: None
Priority: 9
Private: No
Submitted By: Joe English (jenglish)
Assigned to: Joe English (jenglish)
Summary: Panic in [wm stackorder]

Initial Comment:
Reported on the Tcl'ers chat (GPS and stever both replicated):

Running the Tk test suite under the Whim window manager causes a panic in [wm stackorder]

Problem narrowed down to test wm-stackorder-5.2:

++++ wm-stackorder-4.4 PASSED
++++ wm-stackorder-5.1 PASSED
num matched toplevel windows does not equal num children
/bin/sh: line 1: 20192 Aborted




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>Comment By: Donal K. Fellows (dkf)
Date: 2007-12-03 21:48

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If you can get anyone's effort, yes. Block for this. (The fact that
overrideredirect windows might also cause problems is a key factor my
opinion.)

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Comment By: Don Porter (dgp)
Date: 2007-12-03 18:45

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should this bug block 8.5.0 ?

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Comment By: Don Porter (dgp)
Date: 2007-10-25 16:53

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status?

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Comment By: Joe English (jenglish)
Date: 2007-09-17 19:43

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More information: 

[wm stackorder] is computed by calling XQueryTree() on the "vroot" window,
and trying to match each child of the "vroot" against the "reparent" window
of all Tk toplevels.

The "vroot" is either the RootWindow of the display, or the value of the
__SWM_ROOT or __WM_ROOT root window property if present. The "reparent"
window of a Tk toplevel is the ancestor of the client window which is a
child of the "vroot", if it exists; otherwise it is the parent of the
client window (where "client window" is as per the ICCCM).  Both of these
are computed in function "ReparentEvent", called whenever the client window
gets a ReparentNotify.

[wm stackorder] assumes that the "reparent" window of all mapped toplevels
on the same display are children of a common "vroot", and panics if this is
not the case.

There are a number of ways in which this can go wrong: 

(1) There might not be a single virtual root (the EWMH and ICCCM allow for
multiple virtual roots); 
(2) The virtual root might not be identified by __SWM_ROOT or __WM_ROOT
(this appears to be an older, informal convention used -- presumably -- by
Tom LaStrange's "swm"; the EWMH specifies that virtual roots are listed in
_NET_VIRTUAL_ROOTS root window property);
(3) override-redirect windows will not be descendants of any "vroot" if
one is present;
(4) Possible race conditions and other things I'm not clever enough to
think of.

#3 appears to be the cause of the panic in this particular case:
wm-stackorder-5.2 creates two toplevels, one override-redirect and the
other one not, then tests [wm stackorder].  The Whim window manager uses
virtual roots (it uses multiple virtual roots, actually, although that does
not appear to be relevant in this instance.)


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Comment By: Nobody/Anonymous (nobody)
Date: 2007-09-08 07:22

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Stack backtrace here: http://paste.tclers.tk/377

>From which you can see (window_ptr - windows) == 1, table.numEntries == 2,
which triggers the panic.


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