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From Stas Bekman <s...@stason.org>
Subject Re: [mp2] pools that go out of scope aren't a problem anymore?
Date Fri, 26 Nov 2004 23:58:59 GMT
Stas Bekman wrote:
> I've rebuit with --enable-pool-debug CPPFLAGS="-DAPR_BUCKET_DEBUG", but 
> also apr1/httpd2.1
> 
>>>   % ~/perl/5.8.x/bin/perl -MApache2 -MAPR::Pool -MAPR::Table -wle '
>>>   $t= APR::Table::make(APR::Pool->new, 10);   $t->set($_=>$_), print

>>> "Set $_" for 1..20'
>>>
>>>   Segmentation fault
> 
> 
> Now I get the segfault

So trying to go the way Joe has chosen for apreq, I've replaced the plain 
apr_table_make autogenerated wrapper with explicit:

static MP_INLINE SV *mpxs_APR__Table_make(pTHX_ SV *p_sv, int nelts)
{
     apr_pool_t *p = mp_xs_sv2_APR__Pool(p_sv);
     apr_table_t *t = apr_table_make(p, nelts);
     SV *t_sv = mp_xs_APR__Table_2obj(t);
     sv_magic(SvRV(t_sv), p_sv, PERL_MAGIC_ext, Nullch, -1);
     return t_sv;
}

and segfault is gone. here we create a dependency p_sv <- t_sv, so only 
when t_sv goes out of scope the pool object will be destroyed, and this 
code is now safe:

   APR::Table::make(APR::Pool->new, 10);

Unfortunately it doesn't seem like this dependency code can be easily 
integrated with the automatic type conversion, because the code accepts a 
single argument in xs/modperl_xs_sv_convert.h.

At the moment we will need to rewrite all methods that accept the pool 
object, like I did for APR::Table::make above. for example inside 
APR::Table there are also copy() and overlay() that need the same solution.

Any suggestions?

I'm thinking whether we could use the same solution for PV return values 
that use the pool object. For example with server_root_relative(), see the 
end of notes at:
http://perl.apache.org/docs/2.0/api/Apache/ServerUtil.html#C_server_root_relative_
which documents the danger of having the SvPV having a hole in body if the 
pool went out of scope. I guess we can attach the same magical dependency 
there too.

-- 
__________________________________________________________________
Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/     mod_perl Guide ---> http://perl.apache.org
mailto:stas@stason.org http://use.perl.org http://apacheweek.com
http://modperlbook.org http://apache.org   http://ticketmaster.com

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