NAME

Pipeline - Generic pipeline interface

SYNOPSIS

  use Pipeline;
  my $pipeline = Pipeline->new();
  $pipeline->add_segment( @segments );
  $pipeline->dispatch();

DESCRIPTION

"Pipelines" are a mechanism to process data. They are designed to be plugged together to make fairly complex operations act in a fairly straightforward manner, cleanly, and simply.

USING THE PIPELINE MODULE

The usage of the generic pipeline module is fairly simple. You instantiate a Pipeline object by using the new() constructor.

Segments can be added to the pipeline with the add_segment method.

The store that the Pipeline will use can be set by calling the store() method later on. If a store is not set by the time a pipeline is executing then it will use a store of the type "Pipeline::Store::Simple".

To start the pipeline running call the dispatch() method on your Pipeline object.

If a segment returns a Pipeline::Production object then the pipeline will be terminated early and the production will be returned to the user. Regardless of when the pipeline is terminated the pipeline's cleanup pipeline is executed. Segments can be added to the cleanup pipeline either explicitly by calling the cleanups method to get the cleanup pipeline and then adding the segment, or implicitly by returning a segment object from a segment.

To see what is being dispatched within a pipeline dispatch set the pipeline's debug_all value to true.

INHERITANCE

Pipelines are designed to be inherited from. The inheritance tree is somewhat warped and should look a little like this:

     MySegment --> Pipeline::Segment <--- Pipeline

In other words, everything is a pipeline segment.

METHODS

The Pipeline class inherits from the "Pipeline::Segment" class and therefore also has any additional methods that its superclass may have.

init( @_ ): Things to do at construction time. If you do override this, it will often be fairly important that you call and check the value of $self->SUPER::init(@_) to make sure that the setup is done correctly. Returns itself on success, undef on failure. The constructor will fail if you return a false value.
add_segment( LIST ): Adds a segment or segments to the pipeline. Returns itself.
get_segment( INTEGER ): Returns the segment located at the index specified by INTEGER
del_segment( INTEGER ): Deletes and returns the segment located at the index specified by INTEGER
process_results( ARRAYREF ): Examines each result of a segment and calls process_indv_result with each element of ARRAYREF. In the case that process_indv_result returns a production then it is returned to the caller.
process_indv_result( SCALAR ): Examines a single result and does the appripriate thing with it (ie, if it is an object it puts it into the store, if it is a production it returns it to the caller, and if it is a simple value it gets thrown away. In the case that a value is returned from process_indv_result the pipeline should terminate.
dispatch(): Starts the pipeline execution. It calls process_results on anything that a segment returns. The pipeline always returns the production or true.
dispatch_loop( Pipeline, [ ARRAYREF ] ): The "dispatch_loop" method performs the processing for the pipeline
start_dispatch: Prepares all elements of the pipeline to begin processing a segment.
end_dispatch: Cleans up all elements of the pipeline after processing a segment.
dispatch_segment( Pipeline::Segment ): The "dispatch_segment" method handles the execution of an individual segment object.
dispatcher( [Pipeline::Dispatch] ): The "dispatcher" method gets and sets the pipeline dispatcher object that will be used to traverse the pipeline.
cleanups(): Returns the cleanup pipeline. This is a pipeline in and of itself, and all the methods you can call on a pipeline can also be called on this.
cleanup(): Calls the dispatch method on the cleanup pipeline.
segments( [ value ] ): "segments" gets and sets the value of the pipeline list. At initialization this is set to an array reference.
debug_all( value ): Sets debug( value ) recursively for each segment in this pipeline.

AUTHORS

  James A. Duncan <jduncan@fotango.com>
  Leon Brocard <acme@astray.com>