"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.
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:
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 );
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;
}
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Sub::Call::Tail − Tail calls for subroutines and methods |
Paul Evans <[email protected]>