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
              structures 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 example, 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://sourceforge.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)
