Provided by: libchi-perl_0.61-1_all 
NAME
CHI::Driver::Development - Manual for developing new CHI drivers
VERSION
version 0.61
SYNOPSIS
package CHI::Driver::MyDriver;
use Moo;
use strict;
use warnings;
extends 'CHI::Driver';
has ...;
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');
MOO / MOOSE
CHI driver classes must be Moo or Moose based to be fully functional, since we use Moose
roles to implement various features. For backward compatibility, non-Moo/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 BUILD method if you want to process any options specific to your driver.
This is a standard Moo/Moose feature.
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 ( $self )
Return namespaces associated with the cache. It is acceptable to either include or
omit namespaces with no valid keys.
DISCARD POLICIES
You can create new discard policies for size aware caches, to choose items to discard when
the cache gets full. For example, the Memory driver implements an LRU policy.
To implement a discard policy foo, define a subroutine discard_policy_foo, which takes a
driver object and returns a closure that returns one key each time it is called. The
closure should maintain state so that each key is only returned once.
For example, here's the Memory driver's LRU implementation. It utilizes a hash containing
the last used time for each key.
sub discard_policy_lru {
my ($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 it 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 testing_driver_class { 'CHI::Driver::MyDriver' }
sub new_cache_options {
my $self = shift;
return (
$self->SUPER::new_cache_options(),
# Any necessary 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.
Test cleanup
You are responsible for cleaning up your datastore after tests are done. The easiest way
to do this is to place your datastore wholly inside a temporary directory, or use a guard
to remove it at process end.
For example, the File, FastMmap, and DBI tests place all data inside a tempdir that is
automatically cleaned up at process end.
SEE ALSO
CHI
AUTHOR
Jonathan Swartz <swartz@pobox.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2021 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.