Bugs item #1338280, was opened at 2005-10-26 05:53
Message generated for change (Comment added) made by dgp
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Category: 07. Variables
Group: current: 8.4.11
Status: Open
Resolution: None
Priority: 9
Submitted By: miguel sofer (msofer)
Assigned to: miguel sofer (msofer)
Summary: unset traces during namespace delete misbehave

Initial Comment:
(neuronstorm reports in clt:
http://groups.google.com/group/comp.lang.tcl/browse_frm/thread/91073af364234a81/3a1aa30e489f
3eb0#3a1aa30e489f3eb0

The following script demonstrates an invalid result
(empty string element in list) from [info vars
?pattern?] during unset traces called during [namespace
delete].

----

 namespace eval ::ref {}

 set ::ref::var1 AAA
 trace add variable ::ref::var1 {unset} [list doTrace]

 set ::ref::var2 BBB
 trace add variable ::ref::var2 {unset} [list doTrace]

 proc doTrace {vtraced vidx op} {
        puts stdout "'[info vars ::ref::*]'"
 }

 namespace delete ::ref

 puts stdout "'[info vars ::ref::*]'"

----

Output on windows Tcl 8.5a4 is:
 '::ref::var1 ::ref::var2'
 '{} ::ref::var2'
 ''

Output on windows Tcl 8.4.5 is:
 '::ref::var1 ::ref::var2'
 '::ref::var2'
 ''

Tcl8.4.7 behaves like 8.4.5, core-8-4-branch like 8.5a4

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

> Comment By: Don Porter (dgp)
Date: 2005-10-31 23:26

Message:
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the patch does introduce a
script-visible change, yes.

it's also a simple change
that fixes this bug and
allegedly 1337229.

Neither the tcl nor the
tcllib test suite care about
the change.

If something does care, then
let's think harder about this, but
not until we find something that
does care.

Crafting a fix for these bugs other
than the one attached here will
be very, very tricky indeed.  Unless
we delay variable unset traces until
the point where the namespace
variables are no longer accessible,
then the access must go somewhere,
and we're left with the recursive task
of cleaning *that* up.

I fear we may already have that
problem with command delete traces.

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

Comment By: miguel sofer (msofer)
Date: 2005-10-31 16:45

Message:
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Patch not committed: it contradicts the comment in
TclTeardownNamespace:
 /*
  * Start by destroying the namespace's variable table,
  * since variables might trigger traces.
  */

In particular, the patch changes the behaviour of the script:

  namespace eval a {
      proc p {} {puts hi}
      trace add variable x unset {a::p;#}
      set x 1
   }
   namespace delete a

which prints 'hi' before the patch, and does not after the
patch. Note that these comments in the source are the only
documentation about the ordering of operations during
namespace deletion.

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

Comment By: Don Porter (dgp)
Date: 2005-10-31 14:25

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attached patch corrects the reported
problem and passes the test suite.


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

Comment By: miguel sofer (msofer)
Date: 2005-10-29 15:02

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The fundamental problem is that, when a variable is unset
due to its namespace being deleted,  the variable exists
while the unset trace is running:

namespace eval a {trace add variable x unset {puts [catch
{set ::a::x}];#}; set x 1}
1
% unset a::x
1
% namespace eval a {trace add variable x unset {puts [catch
{set ::a::x}];#}; set x 1}
1
% namespace delete a
0

This is a very old bug - just verified that Tcl8.3.4 has it
too. It is probably also the cause of Bug 1337229.

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

Comment By: miguel sofer (msofer)
Date: 2005-10-29 14:58

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As the order in which the variables are deleted is not
specified, this script has been modified an added to the
testsuite as Test trace-18.4:
    namespace eval ::ref {}
    set ::ref::var1 AAA
    trace add variable ::ref::var1 unset doTrace
    set ::ref::var2 BBB
    trace add variable ::ref::var2 {unset} doTrace
    proc doTrace {vtraced vidx op} {
	global info
	append info [catch {set ::$vtraced}][llength [info vars
::ref::*]]
    }
    set info {}
    namespace delete ::ref
    rename doTrace {}
    set info

Note that the returned value is 0201 up to 8.4.7, and 0202
for HEAD and 8-4-branch. 

Note also that the *correct* return value is 1110 - as a
variable should not exist when it's unset trace is running.


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

Comment By: miguel sofer (msofer)
Date: 2005-10-26 08:52

Message:
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user_id=148712

On the basis of which versions are buggy, this is presumed
to be caused by the 2004-05-22 commit.

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

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