mp2: should we allow more than one perl inside non-threaded mpm procs?

[Stas Bekman]

OK, I think I have nailed down one of the biggest troubles, that the recent 
change of MaxClients from 1 to 2 has revealed.

The problem is that currently we allow PerlOptions +Parent/+Clone in the 
prefork mpm, so this:

    <IfDefine PERL_USEITHREADS>
        # a new interpreter pool
        PerlOptions +Parent
    </IfDefine>
Creates two perl interpreters in the same process (there are no threads). And 
it actually works (almost), so two developers can share one prefork mpm 
server, each having a different @INC. Of course your memory usage doubles.

The problem is that the code has different assumptions on when it should 
handle this situation and when not. e.g. it must duplicate the handler 
structure for each perl, but currently it does:

#ifdef USE_ITHREADS
    if (p && !MpHandlerPARSED(handler) && !MpHandlerDYNAMIC(handler)) {
        MP_dSCFG(s);
        if (scfg->threaded_mpm) {
            /*
             * cannot update the handler structure at request time without
             * locking, so just copy it
             */
            handler = *handp = modperl_handler_dup(p, handler);
            duped = 1;
            }
    }
#endif
so it breaks mp2/prefork mpm on certain tests combinations. one is when a 
vhost with +Parent happens to load TestHooks::trans first, and when the parent 
process wants to run it, it thinks it has it loaded (because the handler 
wasn't dupped) and then we get the now infamous 'not a CODE reference' error.

So there are two paths to go from here, the simplest don't allow more than one 
perl per process in the prefork mpm and cleanup any redundant code that is 
currently run for nothing (most of the code within #ifdef USE_ITHREADS .. 
#endif). Probably should introduce a new define APACHE_THREADED_MPM instead of 
using USE_ITHREADS.

The second is to go and fix all the places where scfg->threaded_mpm check is 
done to accomodate the prefork mpm as well.

__________________________________________________________________
Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/     mod_perl Guide ---> http://perl.apache.org
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