6.2. boing.core — The pipeline infrastructure

The module boing.core contains the classes that constitute the infrastructure of Boing pipelines.

class boing.core.Offer(*args, iter=None)

An offer defines the list of products that a producer advertises to be its deliverable objects.

Offer.UNDEFINED can be used to define the producer’s offer, when the real offer cannot be defined a priori. This avoids to have empty offers, when they cannot be predeterminated.

class boing.core.Request

The class Request is an abstract class used by Consumer objects for specifing the set of products they are insterested to. The method test() is used to check whether a product matches the request.

Request.NONE and Request.ANY define respectively a “no product” and “any product” requests.

Request objects may also indicate the internal parts of a product to which a producer may be interested. The method items() returns the sequence of the product’s parts a producer is interested to.

The class Request implements the design pattern “Composite”: different requests can be combined into a single request by using the sum operation (e.g. comp = r1 + r2). A composite request matches the union of the products that are matched by the requests whom it is composed. Request.NONE is the identity element of the sum operation.

Request objects are immutable.

test(product)

Return whether the product matches the request.

items(product)

Return an iterator over the product‘s internal parts (i.e. (key, value) pairs) that match the request.

class boing.core.QRequest(string)

The QRequest is a Request defined by a QPath.

class boing.core.Producer(offer, tags=None, store=None, retrieve=None, haspending=None, parent=None)

A Producer is an observable object enabled to post products to a set of subscribed consumers.

When a producer is demanded to posts a product, for each registered consumer it tests the product with the consumer’s request and only if the match is valid it triggers the consumer.

Each Producer has an Offer (a list of product templates), so it can say if a priori it can meet a consumer’s request.

demandChanged

Signal emitted when the aggregate demand changes.

offerChanged

Signal emitted when its own offer changes.

demandedOfferChanged

Signal emitted when its own demanded offer changes.

aggregateDemand()

Return the union of all the subscribed consumers’ requests.

demandedOffer()

Return the producer’s demanded offer.

meetsRequest()

Return whether the product’s offer meets request.

offer()

Return the producer’s offer.

postProduct(product)

Post product. In concrete terms, it triggers the registered consumers that require product, then it stores the product.

class boing.core.Consumer(request, consume=None, hz=None, parent=None)

A Consumer is an observer object that can be subscribed to many producers for receiving their products. When a producer posts a product, it triggers the registered consumers; the triggered consumers will immediately or at regular time interval demand the producer the new products.

Many consumers can be subscribed to a single producer. Each new product is actually shared within the different consumers, therefore a consumer SHOULD NOT modify any received product, unless it is supposed to be the only consumer.

Consumers have a request. When a producer is demanded to posts a product, it tests the product with the consumer’s request and only if the match is valid it triggers the consumer.

A consumer’s request must be an instance of the class Request. The requests “any product” and “no product” are available.

request()

Return the consumer’s request.

_consume(products, producer)

Consume the products posted from producer.