Re: [Patch mp2] Solving module reloading problems (Apache::Reload) with ModPerl::Util::clear_namespace()

Joe Schaefer wrote:
> Geoffrey Young <geoff@xxxxxxxxxxxxxxxxxxx> writes:
>
> [...]
>
>
> > what if you want to unload just Foo and not Foo::Bar?  CGI and Digest
> > come to mind...
>
>
> It's really hard to make module unloading work 100% reliably because

-1) Perl doesn't keep track of all the necessary bits to allow this cleanly  ;-)

>   0) {modules} != {packages} so reloading a module will influence
>      every package it touches (even the ones you forgot to delete),

Yes, in the case of a module with many package definitions, you are in trouble

>   1) perl sometimes does compile-time tricks to avoid symbol lookups,

Yup, also true.

>   2) symbols are occasionally aliased into other namespaces (eg Exporter), 
>      and those aliases won't get rebound once the new symbol definitions
>      are loaded.

Well, partially true. It just means the existing aliases will be pointing to
the _old_ values for that module. Kinda similar to an external module taking a 
ref
to a sub in the package.

>   ... I'm sure there's a whole bunch more issues 
>       that I'm overlooking (ithreads?)  ...

Simply put, Apache::Reload and friends are trying to wipe out a namespace even
though Perl doesn't quite support that. It's doing it's best and I am not sure
it could ever do a 100% clean job (thinking optimizer, for instance).

> There's always Symbol::delete_package, but it looks pretty
> pedestrian when compared to Philippe's patch.  I certainly
> don't see any harm done by including it in mp2, since it
> may work just fine for the majority of users.

--
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Philippe M. Chiasson m/gozer\@(apache|cpan|ectoplasm)\.org/ GPG KeyID : 88C3A5A5
http://gozer.ectoplasm.org/     F9BF E0C2 480E 7680 1AE5 3631 CB32 A107 88C3A5A5

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