1transfer::copy::queue(n) Data transfer facilities transfer::copy::queue(n)
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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 ?0.1?
18 package require transfer::copy::queue ?0.1?
20 transfer::copy::queue object outchannel ?options...?
22 object destroy
24 object busy
26 object pending
28 object put request
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32
34 This package provides objects which serialize transfer requests for a
35 single channel by means of a fifo queue. Accumulating requests are exe‐
36 cuted in order of entrance, with the first request reaching an idle
37 object starting the execution in general. New requests can be added
38 while the object is active and are defered until all requests entered
39 before them have been completed successfully.
40 When a request causes a transfer error execution stops and all requests
42 coming after it are not served. Currently this means that their comple‐
43 tion callbacks are never triggered at all.
44 NOTE: Not triggering the completion callbacks of the unserved requests
46 after an error stops the queue object is something I am not fully sure
47 that it makes sense. It forces the user of the queue to remember the
48 callbacks as well and run them. Because otherwise everything in the
49 system which depends on getting a notification about the status of a
50 request will hang in the air. I am slowly convincing myself that it is
51 more sensible to trigger the relevant completion callbacks with an
52 error message about the queue abort, and 0 bytes transfered.
53 All transfer requests are of the form
55 {type data options...}
57 where type is in {chan, string}, and data specifies the information to
60 transfer. For chan the data is the handle of the channel containing
61 the actual information to transfer, whereas for string data contains
62 directly the information to transfer. The options are a list of them
63 and their values, and are the same as are accepted by the low-level
64 copy operations of the package transfer::copy. Note how just prepend‐
65 ing the request with transfer::copy::do and inserting a channel handle
66 in between data and options easily transforms it from a pure data
67 structure into a command whose evaluation will perform the request.
68
70 transfer::copy::queue object outchannel ?options...?
71 This command creates a new queue object for the management of
72 the channel outchannel. The fully qualified name of the object
73 command is returned as the result of the command.
74 The only option known is -on-status-change. It is optional and
76 defaults to empty, disabling the reporting of status changes.
77 Otherwise it argument is command prefix which is invoked when‐
78 ever the internal status of the object changed. The callback is
79 invoked with two additional arguments, the result of the methods
80 pending and busy, in this order. This allows any user to easily
81 know, for example, when the object has processed all outstanding
82 requests.
83 object destroy
85 This method destroys the object. Doing so while the object is
86 busy will cause errors later on, when the currently executed
87 request completes and tries to access the now missing data
88 structures of the destroyed object.
89 object busy
91 This method returns a boolean value telling us if the object is
92 currently serving a request (i.e. busy, value True), or not
93 (i.e. idle, value False).
94 object pending
96 This method returns the number of requests currently waiting in
97 the queue for their execution. A request currently served is not
98 counted as waiting.
99 object put request
101 This method enters the transfer request into the object's queue
102 of waiting requests. If the object is idle it will become busy,
103 immediately servicing the request. Otherwise servicing the new
104 request will be defered until all preceding requests have been
105 served.
106
108 A possible application of this package and class is within a HTTP 1.1
109 server, managing the results waiting for transfer to the client.
110 It should be noted that in this application the system also needs an
112 additional data structure which keeps track of outstanding results as
113 they may come back in a different order than the requests from the
114 client, and releases them to the actual queue in the proper order.
115
117 This document, and the package it describes, will undoubtedly contain
118 bugs and other problems. Please report such in the category transfer
119 of the Tcllib SF Trackers [http://source‐
120 forge.net/tracker/?group_id=12883]. Please also report any ideas for
121 enhancements you may have for either package and/or documentation.
122
124 channel, copy, queue, transfer
125
127 Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>
128transfer 0.1 transfer::copy::queue(n)