[Tcl-bugs] [ tktoolkit-Bugs-1414171 ] Text widget dumps core with -command option

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Bugs item #1414171, was opened at 2006-01-25 00:47
Message generated for change (Comment added) made by vincentdarley
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Category: 18. [text]
Group: obsolete: 8.4.9
Status: Open
Resolution: Out of Date
Priority: 8
Submitted By: Peter MacDonald (pcmacdon)
Assigned to: Vince Darley (vincentdarley)
Summary: Text widget dumps core with -command option

Initial Comment:
The text widget can be made to dump core with
the following simple script (on 8.4.9 on Linux), when
the dump -command is used where the command adds a tag.

With more complex scripts 8.3 and 8.5 also dump core.
Below is the coredump traceback which seems to
show that segPtr->typePtr->name has been invalidated.

###########################################
pack [text .t]
.t insert end "abc\n" a "---" {} "def" b "   \n" {}
"ghi\n" c
.t tag configure b -background red

proc Dumpy {key value index} {
  puts "KK: $key, $value"
  if {$value == "b" && $key == "tagon"} {
puts TAGGING
    .t tag add $value [list $index linestart] [list
$index lineend]
  }
}
.t dump -all -command Dumpy 1.0 end
##############################################

#0  0x080c18af in DumpLine (interp=0x8132660,
textPtr=0x81c9e90, what=31, 
    linePtr=0x8178430, startByte=0, endByte=32000000,
lineno=1, 
    command=0x81c1218 "Dumpy")
    at
/home/pcmacdon/Tcl/tk8.4.9/unix/../generic/tkText.c:2654
2654                if ((what & TK_DUMP_MARK) &&
(segPtr->typePtr->name[0] == 'm')) {
(gdb) p segPtr
$1 = (TkTextSegment *) 0x81760f8
(gdb) p segPtr->typePtr
$2 = (struct Tk_SegType *) 0x6c2f7273
(gdb) p segPtr->typePtr->name
Cannot access memory at address 0x6c2f7273
(gdb) p what
$3 = 31

(gdb) bt
#0  0x080c18af in DumpLine (interp=0x8132660,
textPtr=0x81c9e90, what=31, 
    linePtr=0x8178430, startByte=0, endByte=32000000,
lineno=1, 
    command=0x81c1218 "Dumpy")
    at
/home/pcmacdon/Tcl/tk8.4.9/unix/../generic/tkText.c:2654
#1  0x080c16f1 in TextDumpCmd (textPtr=0x81c9e90,
interp=0x8132660, argc=7, 
    argv=0xbfffeeb8)
    at
/home/pcmacdon/Tcl/tk8.4.9/unix/../generic/tkText.c:2582
#2  0x080be1d4 in TextWidgetCmd (clientData=0x81c9e90,
interp=0x8132660, 
    argc=7, argv=0xbfffeeb8)
    at
/home/pcmacdon/Tcl/tk8.4.9/unix/../generic/tkText.c:849
#3  0x40034417 in TclInvokeStringCommand ()
   from /home/pcmacdon/usr/lib/libtcl8.4.so
#4  0x400354c7 in TclEvalObjvInternal ()
   from /home/pcmacdon/usr/lib/libtcl8.4.so
#5  0x40035f1d in Tcl_EvalEx () from
/home/pcmacdon/usr/lib/libtcl8.4.so
#6  0x40072093 in Tcl_FSEvalFile () from
/home/pcmacdon/usr/lib/libtcl8.4.so
#7  0x40071157 in Tcl_EvalFile () from
/home/pcmacdon/usr/lib/libtcl8.4.so
#8  0x0805635f in Tk_MainEx (argc=1, argv=0xbffff518, 
    appInitProc=0x8055fbc <Tcl_AppInit>, interp=0x8132660)
    at
/home/pcmacdon/Tcl/tk8.4.9/unix/../generic/tkMain.c:242
#9  0x08055fa4 in main (argc=2, argv=0xbffff514)
    at /home/pcmacdon/Tcl/tk8.4.9/unix/tkAppInit.c:68
#10 0x42017499 in __libc_start_main () from
/lib/i686/libc.so.6


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

>Comment By: Vince Darley (vincentdarley)
Date: 2006-03-25 22:36

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Please test the attached patch for cvs head.

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

Comment By: Nobody/Anonymous (nobody)
Date: 2006-03-25 19:49

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I suspect this can be fixed by keeping track of whether the
widget has been touched when '-command' is called, and if
so, recomputing all the internal objects (TkTextLine*, etc)
from the current index position. -- Vince.

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

Comment By: Don Porter (dgp)
Date: 2006-03-23 18:44

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thanks for re-verifying.

Since there's a workaround
(don't modify the widget
during a dump), I'm going
to drop prio a bit to no
longer block release.  Still
hope the [text] maintainers
will take a look, though.



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

Comment By: Peter MacDonald (pcmacdon)
Date: 2006-03-23 18:38

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Test script

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

Comment By: Peter MacDonald (pcmacdon)
Date: 2006-03-23 18:35

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Same here: the previous test script no longer triggers the
problem in 8.4.13rc0.  But the attached script triggers the
seg-fault, in all versions of Tk 8.3-8.5.
The only change: removal of the if statement so a tag is
always added.
 
The bottom line: adding a tag while in the middle of a dump
-command is bad news.  I suspect that any real resolution of
this problem will require locking out all modifications to
the widget during [.t dump].

To that end, I tried altering the state to disabled, but the
crash still occurs because [.t tag add] allows changes even
during disabled state.

Thus, unless you are willing to change the observable
behavior of [text], an inDump flag will probably need to
added to textPtr to lock out all changes.


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

Comment By: Don Porter (dgp)
Date: 2006-03-23 17:28

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No crash for me with the
8.4.13 candidate releases.

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

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