NAME¶
CHI::Driver::Development - Manual for developing new CHI drivers
VERSION¶
version 0.58
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) 2012 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.