/ 
CPS-0.19
River stage two • 3 direct dependents • 10 total dependents
/ CPS::Governor

NAME

CPS::Governor - control the iteration of the CPS functions

DESCRIPTION

Objects based on this abstract class are used by the gk* variants of the CPS functions, to control their behavior. These objects are expected to provide a method, again, which the functions will use to re-invoke iterations of loops, and so on. By providing a different implementation of this method, governor objects can provide such behaviours as rate-limiting, asynchronisation or parallelism, and integration with event-based IO frameworks.

CONSTRUCTOR

$gov = CPS::Governor->new

Must be called on a subclass which implements the again method. Returns a new instance of a governor object in that class.

SUBCLASS METHODS

Because this is an abstract class, instances of it can only be constructed on a subclass which implements the following methods:

$gov->again( $code, @args )

Execute the function given in the CODE reference $code, passing in the arguments @args. If this is going to be executed immediately, it should be invoked using a tail-call directly by the again method, so that the stack does not grow arbitrarily. This can be achieved by, for example:

@_ = @args;
goto &$code;

Alternatively, the Sub::Call::Tail may be used to apply syntactic sugar, allowing you to write instead:

use Sub::Call::Tail;
...
tail $code->( @args );

EXAMPLES

A Governor With A Time Delay

Consider the following subclass, which implements a CPS::Governor subclass that calls sleep() between every invocation.

package Governor::Sleep

use base qw( CPS::Governor );

sub new
{
   my $class = shift;
   my ( $delay ) = @_;

   my $self = $class->SUPER::new;
   $self->{delay} = $delay;

   return $self;
}

sub again
{
   my $self = shift;
   my $code = shift;

   sleep $self->{delay};

   # @args are still in @_
   goto &$code;
}

SEE ALSO

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>