[SQL-Ledger] Re: Questions Re sql-ledger debian package

[Izzy Blacklock]

Thanks Chris,

I'd be willing to contribute some time to adding the missing my 
statements and providing patches.  If that's all it is, that's an easy 
fix.  I'll work on that today and submit the patches to Dieter and post 
the patches to sql-ledger at lists.ledger123.com

...Izzy

Chris Travers wrote:
> I too had some interesting discussions on #perl about the issues we
> found in LedgerSMB (Presumably the same problems since it was in the
> codebase we inherited from SQL-Ledger).
>
> The main issues we saw were the "Attempt to free unreferenced scalar"
> issues at various points.
>
> On Thu, Feb 18, 2010 at 9:34 AM, Izzy Blacklock <izzyb at bnsnet.ca> wrote:
>   
>> Thanks Raphael,
>>
>> I'll see what I can shake loose on the sql-ledger side of things.  I have to
>> admit I don't fully understand the problem and don't know the sql-ledger
>> code base enough to really be much help on this myself.  Dieter (the lead
>> developer for SQL-Ledger) seems to think this is a perl bug, but in the
>> chat's I've had in #perl channels, threads support as it is now is here to
>> stay and if it breaks code, that code needs to be updated to compensate.
>> Since I don't understand the problem myself, I'm not sure who is right. :(
>>  I don't think threads are in use in sql-ledger, so I'm not sure why its
>> inclusion would trigger a bug.
>>     
>
> Ok, let me explain the problem.  In a word, both are right.  There is
> a Perl bug which causes some loops where scoping issues occur to throw
>  "Attempt to free unreferenced scalar" errors.  This was a change in
> 5.10 and I have never seen this issue prior to the release of that
> version.  While there are some reports of more recent 5.8 variants
> having the same behavior, we haven't had experience with this in
> LedgerSMB because we fixed problems in the code.
>
> I am not entirely sure what the technical problem is but it has
> something to do with variable reassignment in loops, and properly
> thought-out scoping fixes the problem.  The problem seems to occur
> when a variable (usually in my experience, a reference) is freed at
> the end of the loop but still implicitly in the current scope until
> some time later.  At that point you get an error echoed.  This is a
> bug but probably not a very high priority one for the Perl team
> because, quite frankly, no sane code would ever trigger it.
>
> The problem here is that Dieter either doesn't understand what to do
> to fix the problem (add "my" scopes to variable declarations in loop
> structures).
>
> I haven't been able to create a simple code test on my current
> workstation (Fedora 12) which means either the problem has been fixed
> in Perl (unlikely) or that more is required than a simple loop (more
> likely),  However, I am not sure.
>
>
>   
>> At the end of the day, I need a functioning sql-ledger and right know it
>> looks like that means I need to compile perl without threads.  According to
>> Dieter this is a problem for other projects as well, so maybe there is a
>> need to provide a debian package of perl without threads.
>>     
>
> Most other projects have isolated the resulting issues and fixed them.
>  LedgerSMB included.
>
>   
>>  I know perl is
>> used all over the place in a Debian system, so I'm not sure if doing so will
>> break other things.  This is frankly a problem beyond my ability, but I'd be
>> more then happy to do some testing.  I may even be able to provide a test
>> system or a reproducible test case.
>>
>> Dieter, perhaps you could shed some more light on the details of the
>> problem.  Is there an open perl bug that you could point to?  Do you have a
>> reproducible test case?  Could you provide a list of other projects
>> affected?
>> Thanks everyone for your help in resolving this.  I don't think it makes
>> sense for Debian to be distributing a broken package in stable which I
>> believe is currently the case with the sql-ledger package in Lenny.  If the
>> only short term solution is to provide a threads free version of perl, is
>> that doable?
>>     
>
> The best solution is to isolate the loops where this happens and add
> "my" to the variable name.
>
> Best Wishes,
> Chris Travers
> LedgerSMB Core Member
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