On Friday, November 12, 2010 11:42:51 Oliver Frommel wrote:
> I'd like to know if it's possible to fork an infinite loop in the
> postconfig stage of the Apache lifecycle. I am trying to do it in a file
> that I 'use' in the startup.pl that in turn is called by
> PerlPostConfigRequire. The fork code I am using is almost the same as the
> "Complete fork example" from the book, however I had to remove all
> references to the Apache request $r because it is not available at this
> stage. In the child process I am creating data that is exposed to other
> requests via IPC::Shareable, but the requests just seem to hang.
>
> The code looks like this:
>
> startup.pl:
> ...
> use Datastore::Cache ( );
> ...
>
> Datastore/Cache.pm:
> ...
> if ($kid) {
> ...
> } else {
> tie $H, 'IPC::Shareable', 'Test', {create => 1, mode => 0666};
>
> while(1) {
> my $rnd = rand(5);
> $H = $rnd;
> sleep(60);
> }
> }
>
>
> As you can see, the general problem I am trying to solve is the global
> creation of some data that is subject to global change (not dependent on
> requests) but is available to all requests on a specific URL. Maybe there
> better ways of achieving my general goal than forking?
The fork is certainly not the problem.
<Perl>
sub My::PostConfig {
use IPC::ScoreBoard;
use Apache2::ServerUtil ();
if( Apache2::ServerUtil::restart_count>=2 ) {
$My::sb=SB::anon 0, 0, 3;
my $pid;
select undef, undef, undef, 0.1 until defined($pid=fork);
unless($pid) {
SB::set_extra $My::sb, 2, $$; # PID
SB::set_extra $My::sb, 1, 1; # running
while( SB::get_extra $My::sb, 1 ) {
SB::set_extra $My::sb, 0, int rand 0x7fffffff; # value
sleep 1;
}
SB::set_extra $My::sb, 2, 0; # PID
require POSIX;
POSIX::_exit 0;
kill 'KILL', $$; # just in case _exit() fails
}
}
0;
}
sub My::Reponse {
use Apache2::RequestRec ();
use Apache2::RequestIO ();
my ($r)=...@_;
my @l=SB::get_all_extra $My::sb;
SB::set_extra $My::sb, 1, 0 if $r->args eq 'stop';
$r->content_type('text/plain');
$r->print("value=$l[0], running=$l[1], pid=$l[2]\n");
0;
}
</Perl>
PerlPostConfigHandler My::PostConfig
<Location /test>
SetHandler modperl
PerlResponseHandler My::Response
</Location>
$ curl http://localhost/test
value=380451520, running=1, pid=6265
$ curl http://localhost/test
value=1301930535, running=1, pid=6265
$ curl http://localhost/test?stop
value=1285288548, running=1, pid=6265
$ curl http://localhost/test
value=1285288548, running=0, pid=0
I don't have IPC::Shareable here. So I took IPC::ScoreBoard. IPC::ScoreBoard
can only store integer values but it does that without locking. Instead it
uses atomic operations provided by the hardware. That module is quite new. So
you might expect bugs.
Another module that I use quite extensively is MMapDB. It might be better
suited to your task.
Torsten Förtsch
--
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