Hi.
This refers indirectly to the thread "custom proxy setup with mod_perl", but is more
general, I believe.
For the PerlFixupHandler which was discussed before, I need to compare the current request
URL to a predefined static list of URLs, to decide how exactly to proxy this call.
At the moment, there are about 15 URLs in that list; and I believe that there might, maybe
in some cases, be up to 100.
I suppose that I could make this list of URLs available to the handler by doing something
like this :
<Location />
...
PerlFixupHandler My::Proxy->handler
PerlAddVar CHKU "http://www.site-1.com/";
PerlAddVar CHKU "http://www.site-2.org/path?query";
PerlAddVar CHKU "http://www.site-3.biz/";
PerlAddVar CHKU "http://www.site-4.edu/";
etc.. 50 times
</Location>
and then do
my @list = $r->dir_config('CHKU');
in the handler.
On the other hand, I could also put these URLs in a separate configuration text file, and
have the handler read it at each invocation :
<Location />
...
PerlFixupHandler My::Proxy->handler
PerlSetVar URL_LIST "/etc/apache2/conf/urllist.txt"
</Location>
and in the handler :
my $urllist = $r->dir_config('URL_LIST') || "default.list";
my @list = ();
my $fh;
open($fh,'<',$urllist) or safe_die;
@list = <$fh>;
close $fh;
But neither of these is very satisfying.
The first one above is OK up to 10-20 URLs, but becomes a bit unsightly and
clumsy for more.
The second one has the handler read and parse a file at each invocation (even if the
request URL turns out not to be in the list, and the call should just be proxy-ed as is).
Sounds inefficient.
So, I would like to do this :
Package My::Proxy;
our $URLS;
sub handler {
my $r = shift;
unless (defined($URLS)) {
my $urllist = $r->dir_config('URL_LIST') ||
"/etc/apache2/default_urls.list";
my $fh;
my @list;
open($fh,'<',$urllist) or safe_die;
@list = <$fh>;
close $fh;
$URLS = \@list; # or = [ @list ] ??
}
.. use @$URLS, read-only ..
}
As I understand the above, in a pre-fork MPM, each time Apache forks a new child, at the
first handler invocation $URLS will be undef, and thus the code in the handler will define
it, as a reference to an array of URLs read from the file.
And from then on, the list accessible through $URLS should remain available and unvariable
at each subsequent invocation of this handler (in this child), as long as this Apache
child process lives.
First, I may be wrong in my understanding. (that's a question).
Second, if I am right in the above, then does this same understanding extend to all
possible Apache MPMs ? Or am I creating a horrible risk of some race condition, or memory
leak here ?
