[Tcl-bugs] [ tcl-Bugs-449893 ] traces on array misbehaving

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Bugs item #449893, was opened at 2001-08-10 15:17
Message generated for change (Settings changed) made by dgp
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Category: 45. Traces
Group: None
Status: Open
Resolution: Fixed
>Priority: 8
Submitted By: miguel sofer (msofer)
Assigned to: Don Porter (dgp)
Summary: traces on array misbehaving

Initial Comment:
This shouldn't core-dump!



% info patch

8.4a4

% set x(bar) 0

0

% trace variable x r {set x(foo) 1 ;#}

% trace variable x r {unset -nocomplain x(bar) ;#}

% trace vinfo x

{r {unset -nocomplain x(bar) ;#}} {r {set x(foo) 1 ;#}}

% array get

x                                                                              

": no such element in array

% array get x

Segmentation fault (core dumped)



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Comment By: miguel sofer (msofer)
Date: 2001-12-05 16:39

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Re docs: or with [trace]? Or both?

It is a really something that is relevant to the interplay

between [array get] and [trace] - when there are read traces

on an array that either add or remove an element of the

array.



I'm also not 100% happy with the error message when the

trace unsets the whole array (see test trace-1.13 ): should

it rather return {} and no error as does [array get

nonExistingArray] ?



Reopening the ticket, with lower priority now that the

segfault is gone ...

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Comment By: Don Porter (dgp)
Date: 2001-12-05 16:24

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the patch included no doc changes.  Is there a

best place to document the particular behavior?

In the [array get] docs, perhaps?



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Comment By: miguel sofer (msofer)
Date: 2001-12-05 15:45

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Patch committed to HEAD.

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Comment By: miguel sofer (msofer)
Date: 2001-12-01 19:39

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It is difficult to define what the correct behaviour of

[array get]

should be when there are read traces that modify the array 

structure. 



In discussions on the Tcl'ers Chat with Kevin Kenny and 

Don Porter we agreed that a (the only ?) reasonable

behaviour 

is given by



 proc array-get { aName } {

     set result [list]

     upvar 1 $aName array

     foreach s [array names array] {

         if { [info exists array($s)] } { 

	     # because a trace could have deleted it 

             lappend result $s $array($s)

         }

     }

     return $result

 }



The enclosed patch implements this behaviour and adds three

tests 

for it. These tests cause illegal memory behaviour without

the patch 

to tclVar.c - an access to a previously disposed Tcl_Obj is

detected 

by TCL_MEM_DEBUG. 



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Comment By: Don Porter (dgp)
Date: 2001-08-10 15:37

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Note, a very similar script causes a segfault

in Tcl 8.3.3.  (Change [unset -nocomplain ...]

to [catch {unset ... )



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Comment By: miguel sofer (msofer)
Date: 2001-08-10 15:23

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Bug is also present in 8.3.3 and 8.0.5.

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