NAME
   CHI::Cascade - a cache dependencies (cache and like 'make' utility
   concept)

SYNOPSIS
       use CHI;
       use CHI::Cascade;

       $cascade = CHI::Cascade->new(chi => CHI->new(...));

       $cascade->rule(
           target  => 'unique_name',
           depends => ['unique_name_other1', 'unique_name_other2'],
           code    => sub {
               my ($rule, $target_name, $values_of_depends) = @_;

               # $values_of_depends == {
               #     unique_name_other1 => $value_1,
               #     unique_name_other2 => $value_2
               # }
               # $rule->target     eq      $target_name
               # $rule->depends    ===     ['unique_name_other1', 'unique_name_other2']
               # $rule->dep_values ==      $values_of_depends
               # $rule->params     ==      { a => 1, b => 2 }

               # Now we can calcualte $value
               return $value;
           },
           params  => { a => 1, b => 2 }
       );

       $cascade->rule(
           target  => 'unique_name_other1',
           depends => 'unique_name_other3',
           code    => sub {
               my ($rule, $target_name, $values_of_depends) = @_;

               # $values_of_depends == {
               #     unique_name_other3 => $value_3
               # }

               # computing here
               return $value;
           }
       );

       $value_of_this_target = $cascade->run('unique_name');

DESCRIPTION
   This module is the attempt to use a benefits of caching and 'make'
   concept. If we have many an expensive tasks and want to cache it we can
   split its to small expsnsive tasks and to describe dependencies for
   cache items.

   This module is experimental yet. I plan to improve it near time but some
   things already work. You can take a look for t/* tests as examples.

CONSTRUCTOR
   $cascade = CHI::Cascade->new( %options )

   This method constructs a new "CHI::Cascade" object and returns it.
   Key/value pair arguments may be provided to set up the initial state.
   Options are:

   chi Required. Instance of CHI object. The CHI::Cascade doesn't construct
       this object for you. Please create instance of "CHI" yourself.

   busy_lock
       Optional. Default is *never*. *This is not "busy_lock" option of
       CHI!* This is amount of time (to see "DURATION EXPRESSIONS" in CHI)
       until all target locks expire. When a target is recomputed it is
       locked. If process is to be recomputing target and it will die or OS
       will be hangs up we can dead locks and locked target will never
       recomputed again. This option helps to avoid it. You can set up a
       special busy_lock for rules too.

METHODS
   rule( %options )
       To add new rule to "CHI::Cascade" object. All rules should be added
       before first "run" method

       The keys of %options are:

       target
           Required. A target for "run" and for searching of "depends". It
           can be as scalar text or "Regexp" object created through "qr//"

       depends
           Optional. The scalar, arrayref or coderef values of
           dependencies. This is the definition of target(s) from which
           this current rule is dependent. If *depends* is:

           scalar
               It should be plain text of single dependence of this target.

           arrayref
               An each item of list can be scalar value (exactly matched
               target) or code reference. A subroutine should return a
               scalar value as current dependence for this target at
               runtime. It will get a parameters from "=~" operator against
               "target" matching from "qr//" operator if target is "Regexp"
               object type - please see the section "EXAMPLE" for this
               example.

           coderef
               This subroutine will be executed every time inside *run*
               method if necessary. It will get a parameters from "=~"
               operator against "target" matching from "qr//" operator if
               target is "Regexp" object type. It should return scalar or
               arrayref. The returned value is *scalar* it will be
               considered as single dependence of this target and the
               behavior will be exactly as described for *scalar* in this
               paragraph. If the returned value is *arrayref* it will be
               considered as list of dependencies for this target and the
               behavior will be exactly as described for *arrayref* in this
               paragraph.

       code
           Required. The code reference for computing a value of this
           target. Will be executed if no value in cache for this target or
           any dependence or dependences of dependences and so on will be
           recomputed. Will be executed as $code->( $rule, $target,
           $hashref_to_value_of_dependencies ) *(The API of running this
           code was changed since v0.10)*

           $rule
               An instance of CHI::Cascade::Rule object. You can use it
               object as accessor for some current executed target data
               (plain text of target, for getting of parameters and so on).
               Please to see CHI::Cascade::Rule

           $target
               A current target as plain text (what a target the $cascade
               got from run method)

           $hashref_to_value_of_dependencies
               A hash reference of values of all dependencies for current
               target. Keys in this hash are flat strings of dependecies
               and values are computed or cached ones.

               This module should guarantee that values of dependencies
               will be valid values even if value is "undef". This code can
               return "undef" value as a valid code return but author
               doesn't recommend it. If "CHI::Cascade" could not get a
               valid values of all dependencies of current target before
               execution of this code the last will not be executed (The
               "run" will return "undef").

       params
           You can pass in your code any additional parameters by this
           option. These parameters are accessed in your code through
           params method of CHI::Cascade::Rule instance object.

       busy_lock
           Optional. Default is "busy_lock" of constructor or *never* if
           first is not defined. *This is not "busy_lock" option of CHI!*
           This is amount of time (to see "DURATION EXPRESSIONS" in CHI)
           until target lock expires. When a target is recomputed it is
           locked. If process is to be recomputing target and it will die
           or OS will be hangs up we can dead locks and locked target will
           never recomputed again. This option helps to avoid it.

   run( $target )
       This method makes a cascade computing if need and returns value for
       this target If any dependence of this target of any dependencies of
       dependencies were recomputed this target will be recomputed too.

   touch( $target )
       This method refreshes the time of this target. Here is analogy with
       touch utility of Unix and behaviour as make after it. After "touch"
       all targets are dependent from this target will be recomputed at
       next "run" with an appropriate ones.

STATUS
   This module is experimental and not finished for new features ;-) Please
   send me issues through <https://github.com/Perlover/CHI-Cascade> page

ANALOGIES WITH make
   Here simple example how it works. Here is a direct analogy to Unix make
   utility:

       In CHI::Cascade:            In make:

       rule                        rule
       depends                     prerequisites
       code                        commands
       run( rule_name )            make target_name

FEATURES
   The features of this module are following:

   Computing inside process
       If module needs to compute item for cache we compute inside process
       (no forks) For web applications it means that one process for one
       request could take a some time for computing. But other processes
       will not wait and will get either old previous computed value or
       *undef* value.

   Non-blocking computing for concurrent processes
       If other process want to get data from cache we should not block it.
       So concurrent process can get an old data if new computing is run or
       can get *undef* value. A concurrent process should decide itself
       what it should do after it - try again after few time or print some
       message like 'Please wait and try again' to user.

   Each target is splitted is two items in cache
       For optimization this module keeps target's info by separately from
       value item. A target item has lock & timestamp fields. A value item
       has a computed value.

EXAMPLE
   For example please to see the SYNOPSIS

   When we prepared a rules and a depends we can:

   If unique_name_other1 and/or unique_name_other2 are(is) more newer than
   unique_name the unique_name will be recomputed. If in this example
   unique_name_other1 and unique_name_other2 are older than unique_name but
   the unique_name_other3 is newer than unique_name_other1 then
   unique_name_other1 will be recomputed and after the unique_name will be
   recomputed.

   And even we can have a same rule:

       $cascade->rule(
           target  => qr/^unique_name_(.*)$/,
           depends => sub { 'unique_name_other_' . $_[0] },
           code    => sub {
               my ($rule, $target_name, $values_of_depends) = @_;

               # $rule->qr_params          === ( 3 )
               # $target_name              == 'unique_name_3' if $cascade->run('unique_name_3') was
               # $values_of_depends        == {
               #     unique_name_other_3   => $value_ref_3
               # }
           }
       );

       $cascade->rule(
           target  => qr/unique_name_other_(.*)/,
           code    => sub {
               my ($rule, $target_name, $values_of_depends) = @_;
               ...
           }
       );

   When we will do:

       $cascade->run('unique_name_52');

   $cascade will find rule with qr/^unique_name_(.*)$/, will make =~ and
   will find a depend as unique_name_other_52

AUTHOR
   This module has been written by Perlover <[email protected]>

LICENSE
   This module is free software and is published under the same terms as
   Perl itself.

SEE ALSO
   CHI::Cascade::Rule
       An instance of this object can be used in your target codes.

   CHI This object is used for cache.

   CHI::Driver::Memcached::Fast
       Recommended if you have the Memcached

   CHI::Driver::File
       Recommended if you want to use the file caching instead the
       Memcached for example

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