transfer::copy::queue(n) Data transfer facilities transfer::copy::queue(n) 







transfer::copy::queue - Queued transfers








package require Tcl 8.4


package require snit ?1.0?


package require struct::queue ?1.4?


package require transfer::copy ?0.2?


package require transfer::copy::queue ?0.1?


transfer::copy::queue objectName outchannel
    ?options...?


objectName method ?arg arg ...?


objectName destroy


objectName busy


objectName pending


objectName put request












This package provides objects which serialize transfer requests
    for a single channel by means of a fifo queue. Accumulated requests are
    executed in order of entrance, with the first request reaching an idle
    object starting the execution in general. New requests can be added while
    the object is active and are defered until all requests entered before them
    have been completed successfully.


When a request causes a transfer error execution stops and all
    requests coming after it are not served. Currently this means that their
    completion callbacks are never triggered at all.


NOTE: Not triggering the completion callbacks of the
    unserved requests after an error stops the queue object is something I am
    not fully sure that it makes sense. It forces the user of the queue to
    remember the callbacks as well and run them. Because otherwise everything in
    the system which depends on getting a notification about the status of a
    request will hang in the air. I am slowly convincing myself that it is more
    sensible to trigger the relevant completion callbacks with an error message
    about the queue abort, and 0 bytes transfered.


All transfer requests are of the form




	{type data options...}



where type is in {chan, string}, and
    data specifies the information to transfer. For chan the data
    is the handle of the channel containing the actual information to transfer,
    whereas for string data contains directly the information to
    transfer. The options are a list of them and their values, and are
    the same as are accepted by the low-level copy operations of the package
    transfer::copy. Note how just prepending the request with
    transfer::copy::do and inserting a channel handle in between
    data and options easily transforms it from a pure data
    structure into a command whose evaluation will perform the request.













  

  
This command creates a new queue object for the management of the channel
      outchannel, with an associated Tcl command whose name is
      objectName. This object command is explained in full detail
      in the sections Object command and Object methods. The set
      of supported options is explained in section Options.
    
The object command will be created under the current namespace
        if the objectName is not fully qualified, and in the specified
        namespace otherwise. The fully qualified name of the object command is
        returned as the result of the command.

  










All objects created by the ::transfer::copy::queue command
    have the following general form:



  

  
The method method and its arg'uments determine the exact
      behavior of the command. See section Object methods for the
      detailed specifications.











  

  
This method destroys the object. Doing so while the object is busy will
      cause errors later on, when the currently executed request completes and
      tries to access the now missing data structures of the destroyed
    object.

  

  
This method returns a boolean value telling us if the object is currently
      serving a request (i.e. busy, value True), or not (i.e.
      idle, value False).

  

  
This method returns the number of requests currently waiting in the queue
      for their execution. A request currently served is not counted as
    waiting.

  

  
This method enters the transfer request into the object's queue of
      waiting requests. If the object is idle it will become busy,
      immediately servicing the request. Otherwise servicing the new request
      will be defered until all preceding requests have been served.












The only option known is -on-status-change. It is optional
    and defaults to the empty list, disabling the reporting of status changes.
    Otherwise its argument is a command prefix which is invoked whenever the
    internal status of the object changed. The callback is invoked with two
    additional arguments, the result of the methods pending and
    busy, in this order. This allows any user to easily know, for
    example, when the object has processed all outstanding requests.








A possible application of this package and class is within a HTTP
    1.1 server, managing the results waiting for transfer to the client.


It should be noted that in this application the system also needs
    an additional data structure which keeps track of outstanding results as
    they may come back in a different order than the requests from the client,
    and releases them to the actual queue in the proper order.








This document, and the package it describes, will undoubtedly
    contain bugs and other problems. Please report such in the category
    transfer of the Tcllib SF Trackers
    [http://sourceforge.net/tracker/?group_id=12883]. Please also report any
    ideas for enhancements you may have for either package and/or
  documentation.








channel, copy, queue, transfer








Transfer module








Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>








  

    0.1
    transfer