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Perl Recipe of the Day

The following recipe is from Perl Cookbook, 2nd Edition, by Tom Christiansen and Nathan Torkington. All links in this recipe point to the online version of the book on the Safari Bookshelf.

Buy it now, or read it online on the Safari Bookshelf.

21.13. Sharing Information Between Handlers

21.13.1. Problem

You want to share information between handlers, but global variables are global to a process and not automatically cleaned up after every request.

21.13.2. Solution

Use Apache pnotes (Perl notes):

# in one handler
$r->pnotes("Name", $name);

# in another handler
$name = $r->pnotes("Name");

21.13.3. Discussion

Apache modules communicate with each other using notes (see Recipe 21.11). Apache notes act like a hash attached to a request—one handler stores a value for a key in the hash, so that another handler can read it later. The Perl notes features is also a hash attached to the request object, but it's only for the Perl handlers.

To set a pnote, pass a key and a value to the $r->pnotes method. To retrieve a pnote, pass only the key. You can store complex data structures:

$r->pnotes("Person", { Name => "Nat",
                       Age  => 30,
                       Kids => 2 });
# later
$person = $r->pnotes("Person");

and even objects:

$person = new Person;
$person->name("Nat");
$person->age(30);
$person->kids(2);

$r->pnotes(Person => $person);

# later

$person = $r->pnotes("Person");
# $person is a reference to the same object

21.13.4. See Also

Recipe 8.11 in mod_perl Developer's Cookbook; Apache::Table; pnotes method in the Apache manpage