Kamaelia.Chassis.Carousel.Carousel

Here we go again, and again,...

Descripton

This chassis component is for making a carousel of components. It gets its name from a broadcast carousel - where a programme (or set of programmes) is broadcast one after another, often on a loop. Alternatively, think of public information screens which display a looping carousel of slides of information.

If this makes no sense, suppose you want to read data from a sequence of files - one after another. Provide a carousel with a filereader component and a source of filenames, and it will make a new filereader for each file in turn, outputting their data one after another. The carousel automatically asks the filename source for a new item when its current child signals that it has finished.

You gain reusability from things that are not directly reusable and normally come to a halt.

Examples

Reading from a sequence of files

1. Write a factory function that takes a single argument and returns a new component for the carousel:

def makeFileReader(filename):
    return ReadFileAdapter(filename = filename, ...other args... ) 

2. Make the carousel giving it the factory function:

 carousel = Carousel( componentFactory = makeFileReader )

3. Make a source of instructions for the carousel: (in this case, a source of filenames)

filenames = Chooser( ["file1","file2","file3", ... ] )

4. Wire the source and carousel together:

filecarousel = JoinChooserToCarousel( chooser = filenames, carousel = carousel ) 

5. Activate:

filecarousel.activate()

How does it work?

The carousel chassis creates and encapsulates (as a child) the component you want it to, and lets it get on with it.

Anything sent to the carousel's "inbox" inbox is passed onto the child component. Anything the child sends out appears at the carousel's "outbox" and "signal" outboxes.

If the child sends an Axon.Ipc.shutdownMicroprocess or Axon.Ipc.producerFinished message then the carousel gets rid of that component and sends a "NEXT" message to its "requestNext" outbox.

Another component, such as a Chooser, should respond to this message by sending the new set of arguments (for the factory function) to the carousel's "next" inbox. The carousel then uses your factory function to create a new child component. And so the cycle repeats.

If the argument source needs to receive a "NEXT" message before sending its first set of arguments, then set the argument make1stRequest=True when creating the carousel.

You can send new orders to the next inbox at any time. The carousel will immediately unwire that child (and create the new one) and ask the old child to shut down by sending an Axon.Ipc.shutdownMicroprocess message to its control inbox.

The carousel will shutdown in response to an Axon.Ipc.shutdownMicroprocess or Axon.Ipc.producerFinished message. It will also terminate any child component in the same way as described above.

Pydoc Style Docs

-- Automatic documentation generator, 21 Nov 2008 at 04:01:30 UTC/GMT

class Carousel(Axon.Component.component)

A carousel component that makes child components one at a time and lets them do their stuff. Replacing them when they terminate or if requested to do so.

Inboxes:

• inbox - passthrough to child's inbox "inbox"
• next - where we recieve requests to replace the child component
• control - where we recieve shutdown requests from outside
• _control - internal use : to recieve 'producerFinished' or 'shutdownMicroprocess' from child

Outboxes:

• outbox - passthrough from child's outbox "outbox"
• signal -
• _signal - internal use: for sending 'shutdownMicroprocess' to child

requestNext - for requesting new child component

All methods, except __init__ are private implementation details of the component

__init__(self, componentFactory, make1stRequest=False)

• __init__(componentFactory)
• __init__(componentFactory,make1stRequest=True)
• componentFactory(argument) -> new component
  factory function for creating a new child according to specified arguments
• make1stRequest = True
  Carousel will, immediately after activation, send a "NEXT" message to its "requestNext" outbox. Otherwise the carousel just waits.

handleFinishedChild(self)

Unplugs the child if a shutdownMicroprocess or producerFinished message is received from it. Also sends a "NEXT" request if one has not already been sent.

handleNewChild(self)

If data received on "next" inbox, removes any existing child and creates and wires in a new one.

Received data is passed as an argument to the factory function (supplied at initialisation) that creates the new child.

main(self)

Main loop

requestNext(self)

Sends 'next' out the 'requestNext' outbox

shutdown(self)

Returns True if a shutdownMicroprocess or producerFinished message was received.

unplugChildren(self)

Sends 'shutdownMicroprocess' to children and unwires and disowns them.