Re: shared variable between PerlChildInitHandler and PerlResponseHandler

On Thursday, August 19, 2010 18:24:15 Mark Risher wrote:
> > The only thing where mod_perl may stay in the way here is if you use
> > somehow a 
> > 
> > different interpreter for child_init than for handler. Do you use a
> > threaded  MPM, e.g. windows? Do you use the +Parent PerlOption in a
> > VHost?
> 
> [mr] I haven't changed the MPM, and I'm running on a Linux host. I do not
> have  the +Parent option

httpd -V ?

could you post the httpd.conf?

could you post the complete code (as simplified as possible)?

As an example I have just added the following lines to my httpd.conf:

<Perl>
package My::XX;

use strict;
use Apache2::RequestRec ();
use Apache2::RequestIO ();

my $var;

sub pv {
    my ($prefix)=@_;
    warn "$prefix: var=".(defined $var ? "'$var'" : "UNDEF");
}

sub Init {
    pv 'Init before';
    $var++;
    pv 'Init after';
    0;
}

sub Response {
    my ($r)=@_;

    $r->content_type('text/plain');

    pv 'Response before';
    $var++;
    pv 'Response after';

    $r->print("$var\n");
    0;
}
</Perl>

PerlChildInitHandler My::XX::Init
<Location /My/XX>
  SetHandler modperl
  PerlResponseHandler My::XX::Response
</Location>

After a restart I see these lines in the error_log:

Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.

and each "curl http://localhost/My/XX" produces a pair of these:

Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Init before: var=UNDEF at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Init after: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='3' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='1' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='3' at /etc/opt/apache-prefork/httpd.conf line 442.
Response before: var='2' at /etc/opt/apache-prefork/httpd.conf line 442.
Response after: var='3' at /etc/opt/apache-prefork/httpd.conf line 442.

You see $var gets incremented and it preserves its state between calls. Why do 
I see multiple occurrences of var=2? There are multiple apache instances 
active. Each one has its own perl interpreter. So I have several interpreters 
and hence several $var instances that are incremented independently.

Modify pv() to print out the process ID and you can see it:

sub pv {
    my ($prefix)=@_;
    warn "$$ $prefix: var=".(defined $var ? "'$var'" : "UNDEF");
}

Torsten Förtsch

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