CHI::Memoize - Make functions faster with memoization, via CHI
version 0.07
use CHI::Memoize qw(:all); # Straight memoization in memory memoize('func'); memoize('Some::Package::func'); # Memoize to a file or to memcached memoize( 'func', driver => 'File', root_dir => '/path/to/cache' ); memoize( 'func', driver => 'Memcached', servers => ["127.0.0.1:11211"] ); # Expire after one hour memoize('func', expires_in => '1h'); # Memoize based on the second and third argument to func memoize('func', key => sub { $_[1], $_[2] });
"`Memoizing' a function makes it faster by trading space for time. It does this by caching the return values of the function in a table. If you call the function again with the same arguments, memoize jumps in and gives you the value out of the table, instead of letting the function compute the value all over again." -- quoted from the original Memoize
memoize
For a bit of history and motivation, see
http://www.openswartz.com/2012/05/06/memoize-revisiting-a-twelve-year-old-api/
CHI::Memoize provides the same facility as Memoize, but backed by CHI. This means, among other things, that you can
CHI::Memoize
specify expiration times (expires_in) and conditions (expire_if)
memoize to different backends, e.g. File, Memcached, DBI, or to multilevel caches
handle arbitrarily complex function arguments (via CHI key serialization)
All of these are importable; only memoize is imported by default. use Memoize qw(:all) will import them all as well as the NO_MEMOIZE constant.
use Memoize qw(:all)
NO_MEMOIZE
Creates a new function wrapped around $func that caches results based on passed arguments.
$func can be a function name (with or without a package prefix) or an anonymous function. In the former case, the name is rebound to the new function. In either case a code ref to the new wrapper function is returned.
# Memoize a named function memoize('func'); memoize('Some::Package::func'); # Memoize an anonymous function $anon = memoize($anon);
By default, the cache key is formed from combining the full function name, the calling context ("L" or "S"), and all the function arguments with canonical JSON (sorted hash keys). e.g. these calls will be memoized together:
memoized_function({a => 5, b => 6, c => { d => 7, e => 8 }}); memoized_function({b => 6, c => { e => 8, d => 7 }, a => 5});
because the two hashes being passed are canonically the same. But these will be memoized separately because of context:
my $scalar = memoized_function(5); my @list = memoized_function(5);
By default, the cache namespace is formed from the full function name or the stringified code reference. This allows you to introspect and clear the memoized results for a particular function.
memoize throws an error if $func is already memoized.
See OPTIONS below for what can go in the options hash.
Returns a CHI::Memoize::Info object if $func has been memoized, or undef if it has not been memoized.
# The CHI cache where memoize results are stored # my $cache = memoized($func)->cache; $cache->clear; # Code references to the original function and to the new wrapped function # my $orig = memoized($func)->orig; my $wrapped = memoized($func)->wrapped;
Removes the wrapper around $func, restoring it to its original unmemoized state. Also clears the memoize cache if possible (not supported by all drivers, particularly memcached). Throws an error if $func has not been memoized.
memoize('Some::Package::func'); ... unmemoize('Some::Package::func');
The following options can be passed to "memoize".
Specifies a code reference that takes arguments passed to the function and returns a cache key. The key may be returned as a list, list reference or hash reference; it will automatically be serialized to JSON in canonical mode (sorted hash keys).
For example, this uses the second and third argument to the function as a key:
memoize('func', key => sub { @_[1..2] });
and this is useful for functions that accept a list of key/value pairs:
# Ignore order of key/value pairs memoize('func', key => sub { %@_ });
Regardless of what key you specify, it will automatically be prefixed with the full function name and the calling context ("L" or "S").
If the coderef returns CHI::Memoize::NO_MEMOIZE (or NO_MEMOIZE if you import it), this call won't be memoized. This is useful if you have a cache of limited size or if you know certain arguments will yield nondeterministic results. e.g.
CHI::Memoize::NO_MEMOIZE
memoize('func', key => sub { $is_worth_caching ? @_ : NO_MEMOIZE });
You can pass any of CHI's set options (e.g. expires_in, expires_variance) or get options (e.g. expire_if, busy_lock). e.g.
# Expire after one hour memoize('func', expires_in => '1h'); # Expire when a particular condition occurs memoize('func', expire_if => sub { ... });
Any remaining options will be passed to the CHI constructor to generate the cache:
# Store in file instead of memory memoize( 'func', driver => 'File', root_dir => '/path/to/cache' ); # Store in memcached instead of memory memoize('func', driver => 'Memcached', servers => ["127.0.0.1:11211"]);
Unless specified, the namespace is generated from the full name of the function being memoized.
You can also specify an existing cache object:
# Store in memcached instead of memory my $cache = CHI->new(driver => 'Memcached', servers => ["127.0.0.1:11211"]); memoize('func', cache => $cache);
By default CHI, and thus CHI::Memoize, returns a deep clone of the stored value even when caching in memory. e.g. in this code
CHI
# func returns a list reference memoize('func'); my $ref1 = func(); my $ref2 = func();
$ref1 and $ref2 will be references to two completely different lists which have the same contained values. More specifically, the value is serialized by Storable on set and deserialized (hence cloned) on get.
$ref1
$ref2
set
get
The advantage here is that it is safe to modify a reference returned from a memoized function; your modifications won't affect the cached value.
my $ref1 = func(); push(@$ref1, 3, 4, 5); my $ref2 = func(); # $ref2 does not have 3, 4, 5
The disadvantage is that it takes extra time to serialize and deserialize the value, and that some values like code references may be more difficult to store. And cloning may not be what you want at all, e.g. if you are returning objects.
Alternatively you can use CHI::Driver::RawMemory, which will store raw references the way Memoize does. Now, however, any modifications to the contents of a returned reference will affect the cached value.
Memoize
memoize('func', driver => 'RawMemory'); my $ref1 = func(); push(@$ref1, 3, 4, 5); my $ref2 = func(); # $ref1 eq $ref2 # $ref2 has 3, 4, 5
The caveats of Memoize apply here as well. To summarize:
Do not memoize a function whose behavior depends on program state other than its own arguments, unless you explicitly capture that state in your computed key.
Do not memoize a function with side effects, as the side effects won't happen on a cache hit.
Do not memoize a very simple function, as the costs of caching will outweigh the costs of the function itself.
Memoizing a function will affect its call stack and its prototype.
A number of modules address a subset of the problems addressed by this module, including:
Memoize::Expire - pluggable expiration of memoized values
Memoize::ExpireLRU - provides LRU expiration for Memoize
Memoize::Memcached - use a memcached cache to memoize functions
Questions and feedback are welcome, and should be directed to the perl-cache mailing list:
http://groups.google.com/group/perl-cache-discuss
Bugs and feature requests will be tracked at RT:
http://rt.cpan.org/NoAuth/Bugs.html?Dist=CHI-Memoize bug-chi-memoize@rt.cpan.org
The latest source code can be browsed and fetched at:
http://github.com/jonswar/perl-chi-memoize git clone git://github.com/jonswar/perl-chi-memoize.git
CHI, Memoize
Jonathan Swartz <swartz@pobox.com>
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.
To install CHI::Memoize, copy and paste the appropriate command in to your terminal.
cpanm
cpanm CHI::Memoize
CPAN shell
perl -MCPAN -e shell install CHI::Memoize
For more information on module installation, please visit the detailed CPAN module installation guide.