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Buffering of data items until requested one at a time

PromptedTurnstile buffers items received, then sends them out one at a time in response to requests, first-in first-out style.

This is useful for controlling or limiting the rate of flow of data.

Example Usage

Displaying a script from a file, one line at a time, when a pygame button is clicked:

    SOURCE = RateControlledFileReader("script.txt",readmode="lines", ...),
    GATE   = PromptedTurnstile(),
    SINK   = ConsoleEchoer(),
    NEXT   = Button(label="Click for next line of script"),
    linkages = {
        ("SOURCE", "outbox") : ("GATE", "inbox"),
        ("GATE",   "outbox") : ("SINK", "inbox"),
        ("NEXT",   "outbox") : ("GATE", "next"),

        ("SOURCE", "signal") : ("GATE", "control"),
        ("GATE",   "signal") : ("SINK", "control"),
        ("SINK",   "signal") : ("NEXT", "control"),


Send items to the "inbox" inbox where they will queue up. Then each time you send anything to the "next" inbox; one item will be taken from the queue and forwarded out of the "outbox" outbox.

Think of it like a turnstile gate with people queuing up for it. Each message sent to the "next" inbox is a signal to let one person through the turnstile.

This component supports sending data out of its outbox to a size limited inbox. If the size limited inbox is full, this component will pause until it is able to send out the data. Data will not be consumed from the inbox if this component is waiting to send to the outbox.

If there is a backlog of "next" requests (because there is nothing left in the buffer) those items will be sent out as soon as they arrive. There is no need to send another "next" request.

Send a producerFinished message to the "control" inbox to tell PromptedTurnstile that there will be no more data. When prompted turnstile then receives a "next" request and has nothing left queued, it will send a producerFinised() message to its "signal" outbox and immediately terminate.

If a shutdownMicroprocess message is received on the "control" inbox. It is immediately sent on out of the "signal" outbox and the component then immediately terminates.


class PromptedTurnstile(Axon.Component.component)

PromptedTurnstile() -> new PromptedTurnstile component.

Buffers all items sent to its "inbox" inbox, and only sends them out, one at a time when requested.


  • control : Shutdown signalling
  • inbox : Data items
  • next : Requests to send out items


  • outbox : Data items
  • signal : Shutdown signalling

Methods defined here


You should be using the inbox/outbox interface, not these methods (except construction). This documentation is designed as a roadmap as to their functionalilty for maintainers and new component developers.




Got a problem with the documentation? Something unclear that could be clearer? Want to help improve it? Constructive criticism is very welcome - especially if you can suggest a better rewording!

Please leave you feedback here in reply to the documentation thread in the Kamaelia blog.

-- Automatic documentation generator, 05 Jun 2009 at 03:01:38 UTC/GMT