/ 
CHI-Memoize-0.07
River stage one • 1 direct dependent • 6 total dependents
/ CHI::Memoize

NAME

CHI::Memoize - Make functions faster with memoization, via CHI

VERSION

version 0.07

SYNOPSIS

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] });

DESCRIPTION

"`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

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

FUNCTIONS

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.

memoize ($func, %options)

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.

memoized ($func)

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;
unmemoize ($func)

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');

OPTIONS

The following options can be passed to "memoize".

key

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.

memoize('func', key => sub { $is_worth_caching ? @_ : NO_MEMOIZE });
set and get options

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 { ... });
cache options

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);

CLONED VS RAW REFERENCES

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

# 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.

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('func', driver => 'RawMemory');
my $ref1 = func();
push(@$ref1, 3, 4, 5);
my $ref2 = func();
# $ref1 eq $ref2
# $ref2 has 3, 4, 5

CAVEATS

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.

KNOWN BUGS

  • Memoizing a function will affect its call stack and its prototype.

RELATED MODULES

A number of modules address a subset of the problems addressed by this module, including:

SUPPORT

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

SEE ALSO

CHI, Memoize

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.