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Role, Orientation, InterestType

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Tony Garnock-Jones 2013-05-20 17:56:01 -04:00
parent 11b6e18c7b
commit ea2a091574
1 changed files with 40 additions and 3 deletions
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43
marketplace/scribblings/lowlevel.scrbl
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@ -67,19 +67,56 @@ Roles are almost always constructed by the
implementations themselves. User programs generally only need to
destructure @racket[role] instances.
TODO: Role
A @racket[role] describes the conversational role of a peer as seen by
some process. For example, a subscriber to topic @racket['foo] with
interest-type @racket['participant] might receive a presence
notification carrying the role
@racketblock[(role 'publisher 'foo 'participant)]
Notice that the orientation of the role is the opposite of the
orientation of the endpoint.
}
@deftype[Orientation (U 'publisher 'subscriber)]{
TODO: Orientation
Describes an endpoint's orientation: will it be acting as a publisher
of messages, or as a subscriber to messages? Publishers (orientation
@racket['publisher]) tend to use @racket[send-message] and tend to
respond to feedback from subscribers; subscribers
(@racket['subscriber]) tend to use @racket[send-feedback] and respond
to messages from publishers.
}
@deftype[InterestType (U 'participant 'observer 'everything)]{
TODO: InterestType
Using interest-type @racket['participant] in an endpoint's role
indicates that the endpoint is intending to act as a genuine
participant in whatever protocol is associated with the endpoint and
its topic.
Using @racket['observer] indicates that the endpoint is intended to
@emph{monitor} other ongoing (participant) conversations instead.
Observer endpoints receive presence and absence notifications about
participant endpoints, but participant endpoints only receive
notifications about other participant endpoints, and not about
observer endpoints.
The @racket['observer] interest-type is intended to make it easier to
monitor resource demand and supply. The monitoring endpoints/processes
can react to changing demand by creating or destroying resources to
match.
Finally, the @racket['everything] interest-type receives notifications
about presence and absence of @emph{all} the types of endpoint,
@racket['participant], @racket['observer], and @racket['everything].
Endpoints with interest-type @racket['everything] are rare: they are
relevant for managing demand for @emph{observers}, as well as in some
cases of cross-layer presence/absence propagation. Most programs (and
even most drivers) will not need to use the @racket['everything]
interest-type.
}