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Paul Evans > CPS > CPS::Governor



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


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.


$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.


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 );


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;



Paul Evans <>

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