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  ?0.1?

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

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

       object destroy

       object busy

       object pending

       object 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. Accumulating 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 prepend-
       ing 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

       transfer::copy::queue object outchannel ?options...?
	      This command creates a new queue object for the management of the channel outchannel. The fully qualified name of the object command
	      is returned as the result of the command.

	      The only option known is -on-status-change. It is optional and defaults to empty, disabling the reporting of status changes.  Other-
	      wise it argument is 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, when the object has processed all outstanding requests.

       object 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.

       object 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).

       object 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.

       object 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.

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

COPYRIGHT

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

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