Forum OpenACS Development: Can we use namespace variables to avoid upvar?

Yes you can do it, obviously a lot of time could be spent in this area which would benefit code simplification. The problem is the code most in need of simplifying is difficult to understand! It may prove to be too tedious, but all new work should consider the benefits.

namespace eval ::mylib {
  variable some_var
  set some_var foo
}

that ::mylib::some_var will persist over connections and not be deleted after the end of the connection of the thread's interpreter such as other vars would be?

Do you know in particular if that is true for aolserver 4? That would be quite a serious bug I think.

So this means that we can't still use namespace vars to transfer values?  It has been confirmed by Tils that it still not cleans up the vars.

What is wrong with simply initializing the variable? I guess the question is when and how. Unforutnately ACS, and now OpenACS decided to hog the first preauth filter position with the rp_filter (now rp_resource_filter). It would be nice to move both filters to the postauth position, after authorization takes place, although the resource filter could maybe run in preauth, since it doesn't require auth.

Then packages could run initilization code in preauth, and use trace filters to handle cleanup. You might also have the opportunity to load new packages which protect the site and that should run before database access gets involved (possibly aborting the connection). Right now the only way to do this is to hack in a filter into the private init.tcl file.

In AOLserver there is a convenient proc ns_atclose which might be used to do what you want. Here is an example of it being used with namespace vars:

namespace eval ::twt::db::transaction {

    variable initialized 0
    variable ids
 
    namespace import ::twt::log::*
}


proc ::twt::db::transaction::init { } {

    ns_atclose ::twt::db::transaction::reset
    
    variable initialized 1
    variable ids
    array unset ids

}

proc ::twt::db::transaction::reset { } {

    # This runs after the connection closes

    variable initialized
    variable ids

    # Need to rollback any open transactions
    foreach id [array names ids] {
	
	set transactionInfo $ids($id)
	set provider [lindex $transactionInfo 0]
	set transactionRollbackProc [set ::twt::db::${provider}::transactionRollbackProc]
	$transactionRollbackProc $id
    }
    
    array unset ids
    set initialized 0
}

The namespace vars are reset for each connection. Ns_atclose is guaranteed to run even if the connection returns an error, it also runs at the end of a scheduled procedure, if the code were to be used there.

Watching the logs, I've sort of put together that it falls like this : many requests fall under one connection, and one connection ends the life of a namespace variable.

I guess it has to do with the child interpreter that aolserver uses?

Why hasn't anyone addressed this before? or for Aolserver 4x ?

The reason why namespace vars are an issue in aolserver is that the interpreters are resued. The work pretty much like globals. AOLserver has a way to clean up globals as the end of a request.

Its not really a problem, and I think most existing Tcl packages do something itelligent with namespace vars. It is just something to be aware of when using the variables inside AOLserver.