Provided by: tcllib_1.14-dfsg-1_all bug


       transfer::copy::queue - Queued transfers


       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



       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


       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.

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

       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.

       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.


       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.


       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.


       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
       [].    Please  also  report  any  ideas  for
       enhancements you may have for either package and/or documentation.


       channel, copy, queue, transfer


       Transfer module


       Copyright (c) 2006 Andreas Kupries <>