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



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NAME
       transfer::copy::queue - Queued transfers

SYNOPSIS
       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

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DESCRIPTION
       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.

API
   PACKAGE COMMANDS
       transfer::copy::queue objectName outchannel ?options...?
              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.


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

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


   OBJECT METHODS
       objectName destroy
              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 struc-tures structures
              tures of the destroyed object.

       objectName busy
              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).

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

       objectName put request
              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.


OPTIONS
       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 exam-ple, example,
       ple, when the object has processed all outstanding requests.

USE
       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.

BUGS, IDEAS, FEEDBACK
       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://source -
       forge.net/tracker/? group_id=12883].   Please  also report any ideas for enhancements you may have for
       either package and/or documentation.

KEYWORDS
       channel, copy, queue, transfer

CATEGORY
       Transfer module

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




transfer                                             0.1                            transfer::copy::queue(n)