[Tcl-bugs] [ tcl-Bugs-1348775 ] varTraces leak when variable is unset

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Bugs item #1348775, was opened at 2005-11-04 23:07
Message generated for change (Comment added) made by msofer
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Category: 45. Traces
Group: current: 8.4.11
Status: Open
Resolution: None
Priority: 9
Submitted By: miguel sofer (msofer)
Assigned to: Donal K. Fellows (dkf)
Summary: varTraces leak when variable is unset

Initial Comment:
The new test trace-8.9 shows an 18-byte leak:
        set end [getbytes]
        for {set i 0} {$i < 5} {incr i} {
            set apa {a 1 b 2}
            set bepa [lrange $apa 0 end]
            trace add variable bepa write {error hej}
            catch {set bepa a}
            unset bepa
            set tmp $end
            set end [getbytes]
        }
        expr {$end - $tmp}

This supercedes #1342858, which detected the same leak
but blamed it on [dict].


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>Comment By: miguel sofer (msofer)
Date: 2005-11-07 18:29

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Patch replaced with a slightly-less-icky one (thanks kevin
and joe).

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Comment By: miguel sofer (msofer)
Date: 2005-11-07 17:24

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The attached patch solves the issue for 8.4, in an inelegant
but effective and safe (?) way - assigning to dkf for a
second opinion on this.

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Comment By: miguel sofer (msofer)
Date: 2005-11-07 09:34

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Specifically: the code for [unset] does Tcl_EventuallyFree
the VarTrace, but does not free the contents of its
clientData field. 

Look for a q&d solution in 8-4, and a redesign for 8.5 (see
also #1056134) maybe involving api changes: Tcl_TraceVar
should take also a deletion callback as argument.

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Comment By: miguel sofer (msofer)
Date: 2005-11-07 07:46

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Test trace-8.9 deleted, trace-13.2-4 added to HEAD and
8-4-branch.

When a traced variable is unset, the TraceVarInfo
(clientData in the VarTrace struct) is leaked. This should
be fixed directly in 8.4, and possibly together with
#1056134 in HEAD.

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