[Xotcl] Bug in filter processing?

[Gustaf Neumann]

  Dear Kristoffer,

many things went wrong. It is true, there is a bug in all XOTcl 1.* 
releases,
which is there most likely since many years (8+).

the bug:

   - when a filter chain comes to its end without finding the method
     (e.g. "ob foo"), xotcl records its fact, but this affected as well
     the method invocations from the filter after the "next".

   - The call "$targetclass info ..." was then letal especially
     with the standard unknown handler of the metaclass:
     xotcl belived incorrectly that "info" is unknown, and
     since an "unknown" call on a class (here $targetclass)
     creates an object, it was creating the object "info"
     as instance of that class, and the nightmare turned
     even worse.

I have fixed the bug in 1.6.6, you can obtain it via

    git clone git://alice.wu-wien.ac.at/xotcl

best regards
-gustaf neumann

Am 29.08.10 03:02, schrieb Kristoffer Lawson:
> Take a look at this code:
>
> package require XOTcl 1.6
> namespace import xotcl::*
>
> Class Foo
>
> Foo instproc hello {} {
>      puts hello
> }
>
> Foo instproc myfilter {args} {
>      puts "\nme: [self]"
>      ::set targetclass [my info class]
>      puts "targetclass: $targetclass"
>      puts "calledproc: [self calledproc]"
>      ::set r [next]
>      puts "back from next"
>      puts "paramcmds: [$targetclass info instparametercmd]"
> }
>
> Foo instfilter myfilter
>
> Foo ob
> ob hello
> ob foo
>
>
> So first I have a filter installed which does nothing but print some information, and checks something using the [info] method afterwards. I call an instantiated object with [hello] (an existing method) and again with [foo] (a non-existing method). The latter is when things get interesting. Check the output:
>
>
> me: ::ob
> targetclass: ::Foo
> calledproc: configure
> back from next
> paramcmds:
>
> me: ::ob
> targetclass: ::Foo
> calledproc: init
> back from next
> paramcmds:
>
> me: ::ob
> targetclass: ::Foo
> calledproc: hello
> hello
> back from next
> paramcmds:
>
> me: ::ob
> targetclass: ::Foo
> calledproc: foo
> back from next
>
> me: ::alloc
> ::alloc: unable to dispatch method 'info'
>      while executing
> "my info class"
>      (procedure "cleanup" line 4)
>      ::alloc ::Foo->myfilter
>      ::Foo ::xotcl::Class->recreate
>      ::Foo ::xotcl::Class->create
>      ::Foo ::xotcl::Class->unknown
>      ::Foo ::xotcl::Class->create
>      ::Foo ::xotcl::Class->unknown
>      ::Foo ::xotcl::Class->create
>      ::Foo ::xotcl::Class->unknown
>      invoked from within
> "$targetclass info instparametercmd"
>      (procedure "foo" line 9)
>      ::ob ::Foo->myfilter
>      invoked from within
> "ob foo"
>      (file "filtertest.tcl" line 24)
>
> me: ::alloc
> targetclass: ::Foo
> calledproc: destroy
> back from next
> paramcmds:
>
> me: ::info
> targetclass: ::Foo
> calledproc: destroy
> back from next
> paramcmds:
>
> me: ::ob
> targetclass: ::Foo
> calledproc: destroy
> back from next
> paramcmds:
>
> ...
> So while the [hello] method works as expected, things get totally weird for [foo]. The first thing we notice is that it doesn't jump out at [next] (which should give an error as it does not exist). It continue execution of the filter after [next]. This may or may not be intended, I don't know. The documentation is not clear on this.
>
> More interesting still, we end up with a totally unexpected error. The thing I believe is happening is that, for some reason or other [$targetclass info instparametercmd] is not ending up calling [info] for $targetClass, but creating an object called ::info (and thus overriding the original Tcl command). How [alloc] gets involved in the filter chain too, I am not sure. My guess is that the "unknown method" that resulted from [foo] is being interpreted by the XOTcl $targetclass C implementation as an error that occurred there, and that a new instance called "info" or possibly "alloc" should be created.
>
> This causes major havoc as soon as an unknown method is called. Does the filter code look correct?
>
> This happens with 1.6.2. I had a quick look at CHANGES for later versions and while there was some mention of memory leaks in [info] I wasn't sure if there was anything that would have fixed this.
>
> Any ideas?
>


-- 
Univ.Prof. Dr. Gustaf Neumann
Institute of Information Systems and New Media
WU Vienna
Augasse 2-6, A-1090 Vienna, AUSTRIA