Ubuntu Manpage: transfer::copy::queue

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   Trackers
       [http://core.tcl.tk/tcllib/reportlist].  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>