CHI::Driver::DevelopmeUser)Contributed Perl DocumenCHI::Driver::Development(3)NAMECHI::Driver::Development-- Manual for developing new CHI drivers
VERSION
version 0.55
SYNOPSIS
package CHI::Driver::MyDriver;
use Moose;
use strict;
use warnings;
extends 'CHI::Driver';
has ...;
__PACKAGE__->meta->make_immutable();
sub fetch {
my ( $self, $key ) = @_;
}
sub store {
my ( $self, $key, $data[, $expires_in] ) = @_;
}
sub remove {
my ( $self, $key ) = @_;
}
sub clear {
my ($self) = @_;
}
sub get_keys {
my ($self) = @_;
}
sub get_namespaces {
my ($self) = @_;
}
DESCRIPTION
This document describes how to implement a new CHI driver.
The easiest way to start is to look at existing drivers, such as
CHI::Driver::Memory and CHI::Driver::FastMmap.
NAMING
If you are going to publicly release your driver, call it
'CHI::Driver::something' so that users can create it with
CHI->new(driver => 'I<something>');
If it's an internal driver, you can call it whatever you like and
create it like
CHI->new(driver => '+My::Internal::CHI::Driver');
MOOSE
CHI driver classes must be Moose based to be fully functional, since we
use Moose roles to implement various features. For backward
compatibility, non-Moose drivers will still work at a basic level, but
you will see an error if using any feature requiring a role.
All drivers must directly or indirectly extend CHI::Driver.
NAMESPACE
All cache handles have an assigned namespace that you can access with
"$self->namespace". You should use the namespace to partition your data
store. That is, two cache objects with different namespaces should be
able to access the same key without any collision.
Examples:
· The Memory driver uses a separate sub-hash inside its main memory
hash for each namespace.
· The File driver uses a separate top-level directory for each
namespace.
· The FastMmap driver uses a separate Cache::FastMmap file for each
namespace.
METHODS
Required methods
The following methods have no default implementation, and MUST be
defined by your subclass:
store ( $self, $key, $data[, $expires_in] )
Associate $data with $key in the namespace, overwriting any
existing entry. Called by "set". $data will contain any necessary
metadata, including expiration options, so you can just store it as
a single block.
$expires_in is optionally the number of seconds from now when the
entry will expire. This will only be passed if "expires_on_backend"
in CHI is set. If your driver does not support expiration, or if
you'd rather just let CHI manage expiration, you can ignore this.
fetch ( $self, $key )
Returns the data associated with $key in the namespace. Called by
"get". The main CHI::Driver superclass will take care of
extracting out metadata like expiration options and determining if
the value has expired.
remove ( $self, $key )
Remove the data associated with the $key in the namespace.
clear ( $self )
Remove all data associated with the namespace. (Technically not
required, but the default implementation, which iterates over all
keys and calls "remove" for each, is very inefficient).
Overridable methods
The following methods have a default implementation, but MAY be
overridden by your subclass:
BUILD ( $self, $options )
Define the Moose BUILD method if you want to process any options
specific to your driver.
fetch_multi_hashref ( $keys )
Override this if you want to efficiently process multiple fetches.
Return a hash reference from keys to fetched data. If a key is not
available, it may be left out of the hash or paired with undef. The
default method will iterate over $keys and call fetch for each.
This method is called by get_multi_arrayref and get_multi_hashref.
store_multi ( $key_data, $options )
Override this if you want to efficiently process multiple stores.
$key_data is a hash of keys and data that should be stored. The
default will iterate over $key_data and call store for each pair.
This method is called by set_multi.
Optional methods
The following methods have no default implementation, and MAY be
defined by your subclass, but are not required for basic cache
operations.
get_keys ( $self )
Return all keys in the namespace. It is acceptable to either
include or omit expired keys.
get_namespaces ( $self )
Return namespaces associated with the cache. It is acceptable to
either include or omit namespaces with no valid keys.
DISCARD POLICIES
You can create new discard policies for CHI/SIZE AWARENESS caches, to
choose items to discard when the cache gets full. For example, the
Memory driver implements an LRU policy.
To implement a discard policy foo, define a subroutine
discard_policy_foo, which takes a driver object and returns a closure
that returns one key each time it is called. The closure should
maintain state so that each key is only returned once.
For example, here's the Memory driver's LRU implementation. It utilizes
a hash containing the last used time for each key.
sub discard_policy_lru {
my ($self) = @_;
my $last_used_time = $self->{metadata_for_namespace}->{last_used_time};
my @keys_in_lru_order =
sort { $last_used_time->{$a} <=> $last_used_time->{$b} } $self->get_keys;
return sub {
shift(@keys_in_lru_order);
};
}
You can set the default discard policy for your driver by overriding
default_discard_policy; otherwise the default is 'arbitrary'.
sub default_discard_policy { 'lru' }
TESTING
CHI has a standard set of unit tests that should be used to ensure your
driver is fully implementing the CHI API.
To use CHI's tests (replacing MyDriver with the name of your driver):
· Install Test::Class, and add Test::Class to the build dependencies
for your distribution.
· Add a module called CHI::Driver::MyDriver::t::CHIDriverTests to
your distribution containing:
package CHI::Driver::MyDriver::t::CHIDriverTests;
use strict;
use warnings;
use CHI::Test;
use base qw(CHI::t::Driver);
sub new_cache_options {
my $self = shift;
return (
$self->SUPER::new_cache_options(),
driver => '+CHI::Driver::MyDriver',
# Any other CHI->new parameters for your test driver
);
}
1;
· Add a test script called t/CHI-driver-tests.t to your distribution
containing:
#!perl -w
use strict;
use warnings;
use CHI::Driver::MyDriver::t::CHIDriverTests;
CHI::Driver::MyDriver::t::CHIDriverTests->runtests;
· You may need to override other methods in
CHI::Driver::MyDriver::t::CHIDriverTests, e.g. to skip tests that
do not apply to your driver. See CHI::t::Driver::Memory and
CHI::t::Driver::File in this distribution for examples.
AUTHOR
Jonathan Swartz
SEE ALSO
CHI, CHI::Driver
COPYRIGHT & LICENSE
Copyright (C) 2007 Jonathan Swartz.
CHI is provided "as is" and without any express or implied warranties,
including, without limitation, the implied warranties of
merchantibility and fitness for a particular purpose.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
AUTHOR
Jonathan Swartz <swartz@pobox.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2011 by Jonathan Swartz.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.14.2 2012-07-04 CHI::Driver::Development(3)