1transfer::copy::queue(n) Data transfer facilities transfer::copy::queue(n)
2______________________________________________________________________________
6
8 transfer::copy::queue - Queued transfers
9
11 package require Tcl 8.4
12 package require snit ?1.0?
14 package require struct::queue ?1.4?
16 package require transfer::copy ?0.2?
18 package require transfer::copy::queue ?0.1?
20 transfer::copy::queue objectName outchannel ?options...?
22 objectName method ?arg arg ...?
24 objectName destroy
26 objectName busy
28 objectName pending
30 objectName put request
32______________________________________________________________________________
34
36 This package provides objects which serialize transfer requests for a
37 single channel by means of a fifo queue. Accumulated requests are exe‐
38 cuted in order of entrance, with the first request reaching an idle ob‐
39 ject starting the execution in general. New requests can be added while
40 the object is active and are defered until all requests entered before
41 them have been completed successfully.
42 When a request causes a transfer error execution stops and all requests
44 coming after it are not served. Currently this means that their comple‐
45 tion callbacks are never triggered at all.
46 NOTE: Not triggering the completion callbacks of the unserved requests
48 after an error stops the queue object is something I am not fully sure
49 that it makes sense. It forces the user of the queue to remember the
50 callbacks as well and run them. Because otherwise everything in the
51 system which depends on getting a notification about the status of a
52 request will hang in the air. I am slowly convincing myself that it is
53 more sensible to trigger the relevant completion callbacks with an er‐
54 ror message about the queue abort, and 0 bytes transfered.
55 All transfer requests are of the form
57 {type data options...}
59 where type is in {chan, string}, and data specifies the information to
62 transfer. For chan the data is the handle of the channel containing
63 the actual information to transfer, whereas for string data contains
64 directly the information to transfer. The options are a list of them
65 and their values, and are the same as are accepted by the low-level
66 copy operations of the package transfer::copy. Note how just prepend‐
67 ing the request with transfer::copy::do and inserting a channel handle
68 in between data and options easily transforms it from a pure data
69 structure into a command whose evaluation will perform the request.
70
72 PACKAGE COMMANDS
73 transfer::copy::queue objectName outchannel ?options...?
74 This command creates a new queue object for the management of
75 the channel outchannel, with an associated Tcl command whose
76 name is objectName. This object command is explained in full
77 detail in the sections Object command and Object methods. The
78 set of supported options is explained in section Options.
79 The object command will be created under the current namespace
81 if the objectName is not fully qualified, and in the specified
82 namespace otherwise. The fully qualified name of the object
83 command is returned as the result of the command.
84 OBJECT COMMAND
86 All objects created by the ::transfer::copy::queue command have the
87 following general form:
88 objectName method ?arg arg ...?
90 The method method and its arg'uments determine the exact behav‐
91 ior of the command. See section Object methods for the detailed
92 specifications.
93 OBJECT METHODS
95 objectName destroy
96 This method destroys the object. Doing so while the object is
97 busy will cause errors later on, when the currently executed re‐
98 quest completes and tries to access the now missing data struc‐
99 tures of the destroyed object.
100 objectName busy
102 This method returns a boolean value telling us if the object is
103 currently serving a request (i.e. busy, value True), or not
104 (i.e. idle, value False).
105 objectName pending
107 This method returns the number of requests currently waiting in
108 the queue for their execution. A request currently served is not
109 counted as waiting.
110 objectName put request
112 This method enters the transfer request into the object's queue
113 of waiting requests. If the object is idle it will become busy,
114 immediately servicing the request. Otherwise servicing the new
115 request will be defered until all preceding requests have been
116 served.
117
119 The only option known is -on-status-change. It is optional and defaults
120 to the empty list, disabling the reporting of status changes. Otherwise
121 its argument is a command prefix which is invoked whenever the internal
122 status of the object changed. The callback is invoked with two addi‐
123 tional arguments, the result of the methods pending and busy, in this
124 order. This allows any user to easily know, for example, when the ob‐
125 ject has processed all outstanding requests.
126
128 A possible application of this package and class is within a HTTP 1.1
129 server, managing the results waiting for transfer to the client.
130 It should be noted that in this application the system also needs an
132 additional data structure which keeps track of outstanding results as
133 they may come back in a different order than the requests from the
134 client, and releases them to the actual queue in the proper order.
135
137 This document, and the package it describes, will undoubtedly contain
138 bugs and other problems. Please report such in the category transfer
139 of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
140 also report any ideas for enhancements you may have for either package
141 and/or documentation.
142 When proposing code changes, please provide unified diffs, i.e the out‐
144 put of diff -u.
145 Note further that attachments are strongly preferred over inlined
147 patches. Attachments can be made by going to the Edit form of the
148 ticket immediately after its creation, and then using the left-most
149 button in the secondary navigation bar.
150
152 channel, copy, queue, transfer
153
155 Transfer module
156
158 Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>
159tcllib 0.1 transfer::copy::queue(n)