transfer::copy::queue(3tcl)Data transfer facilitiestransfer::copy::queue(3tcl)______________________________________________________________________________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
_________________________________________________________________DESCRIPTION
This package provides objects which serialize transfer requests for a
single channel by means of a fifo queue. Accumulated requests are exe‐
cuted 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 comple‐
tion 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
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 behav‐
ior 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 addi‐
tional 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://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(3tcl)
