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Logging.h
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1 //# Logging.h: Send, record, and filter informational messages
2 //# Copyright (C) 1996,1997,2004
3 //# Associated Universities, Inc. Washington DC, USA.
4 //#
5 //# This library is free software; you can redistribute it and/or modify it
6 //# under the terms of the GNU Library General Public License as published by
7 //# the Free Software Foundation; either version 2 of the License, or (at your
8 //# option) any later version.
9 //#
10 //# This library is distributed in the hope that it will be useful, but WITHOUT
11 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 //# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
13 //# License for more details.
14 //#
15 //# You should have received a copy of the GNU Library General Public License
16 //# along with this library; if not, write to the Free Software Foundation,
17 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
18 //#
19 //# Correspondence concerning AIPS++ should be addressed as follows:
20 //# Internet email: aips2-request@nrao.edu.
21 //# Postal address: AIPS++ Project Office
22 //# National Radio Astronomy Observatory
23 //# 520 Edgemont Road
24 //# Charlottesville, VA 22903-2475 USA
25 //#
26 //# $Id$
27 
28 #ifndef CASA_LOGGING_H
29 #define CASA_LOGGING_H
30 
31 #include <casacore/casa/aips.h>
32 
38 
39 namespace casacore { //# NAMESPACE CASACORE - BEGIN
40 
41 // <module>
42 //
43 // <summary>
44 // Send, record, and filter informational messages.
45 // </summary>
46 
47 // <prerequisite>
48 // <li> General Casacore utility classes, such as String.
49 // </prerequisite>
50 
51 // <reviewed reviewer="wbrouw" date="1996/08/21" demos="dLogging.cc" tests="tLogging.cc">
52 // </reviewed>
53 
54 // <etymology>
55 // Logging, as in "log book", or "processing log."
56 // </etymology>
57 //
58 // <synopsis>
59 // The classes in the logging module have two essential purposes:
60 // <ol>
61 // <li> To attach processing logs to datasets to retain a permanent history of
62 // informational messages that describe how the dataset arrived at its
63 // present state; and
64 // <li> To inform the user about the progress and decisions made by various
65 // algorithms, such as those used in the Measures system.
66 // </ol>
67 //
68 // The two fundamental classes in the Logging module are the
69 // <linkto class="LogMessage">LogMessage</linkto> and
70 // <linkto class="LogSink">LogSink</linkto> classes.
71 // However, the class which is most of interest to application programmers is
72 // the <linkto class=LogIO>LogIO</linkto> class since it forms the usual
73 // interface to logging.
74 //
75 // A <src>LogMessage</src> consists of an informational message tagged with the
76 // time, a priority (<src>DEBUGGING, NORMAL,</src>, <src>WARN</src>, or
77 // <src>SEVERE</src>) and the source code location of the origin of the message
78 // (for use in debugging primarily).
79 //
80 // The <src>LogSink</src> is used to send the <src>LogMessage</src> to its
81 // destinations. Usually the message will be sent to both a global sink,
82 // intended for user information (e.g., a GUI window), and to a sink associated
83 // with the dataset(s) which are being modified. In practice, the application
84 // programmer does not need to worry about where the global messages go, that
85 // policy is implemented by the Tasking system. In practice, global messages
86 // will be sent to Glish, where they will appear in a GUI, unless Glish is
87 // not available, in which case SEVERE messsages (only) will be sent to
88 // stdout. However, the principle is that "ordinary" application programmers
89 // shouldn't worry about the details of the global sink - they should just
90 // use it.
91 //
92 // A <linkto class="LogFilter">LogFilter</linkto> can be used to filter
93 // messages (based on priority only at the moment) before they are sent to
94 // their appropriate sink(s).
95 //
96 // The <linkto class="LogIO">LogIO</linkto> class puts an ostream like
97 // interface on top of the loggins system. Basically, the application
98 // programmer just has to create messages using and <src>os << items</src>
99 // type interface.
100 //
101 // The first issue that the application programmer has to decide is whether
102 // to use logging at all, or if instead he should put his messages into a
103 // <linkto class="String">String</linkto> or an <src>ostream</src>. It is
104 // never wrong to use log messages, however it is reasonable for low level
105 // classes to use <src>String</src>s or <src>ostream</src>s, since the
106 // caller of that class will have the opportunity to put the text in a log
107 // message if he decides that's the most appropriate thing to do. Note that
108 // it is always wrong to write directly to <src>cout</src> or
109 // <src>cerr</src> (other
110 // then for debugging) - use an <src>ostream</src>, so the caller can replace
111 // it with, for example, an <src>ostringstream</src>.
112 //
113 // Once you decide to use logging, the application programmer only has
114 // to decide at every location he wants to log:
115 // <ol>
116 // <li> What content do you want the message to have; and
117 // <li> what priority does the message have (DEBUGGING, NORMAL, WARN, SEVERE).
118 // </ol>
119 // Schematically, application programmers would use the logging system as
120 // follows:
121 // <srcBlock>
122 // #include <casacore/casa/Logging.h>
123 // ...
124 // void MyClass:myFunction(LogIO &os)
125 // {
126 // os << LogIO::NORMAL << LogOrigin("MyClass", "myFunction()", WHERE); // 1
127 // ...
128 // os << WHERE << "An informative message") << LogIO::POST; // 2
129 // if (error()) {
130 // os << WHERE << LogIO::SEVERE << "Error!" << LogIO::POST; // 3
131 // sink.post(msg);
132 // ...
133 // }
134 // }
135 // </srcBlock>
136 // <ol>
137 // <li> Set up the location where log messages come from. WHERE will expand
138 // into the file name and line number (useful for debugging). Set the
139 // priority to NORMAL (this is the default, but you don't know what
140 // the state of <src>os</src> is when it is passed in to this function).
141 // <li> Set the message and the new line number (optional but encouraged) and
142 // post it.
143 // <li> Change the priority to SEVERE and post an error message.
144 // </ol>
145 //
146 // When a dataset is created from several other datasets, their input
147 // "histories" should be merged if possible. This can be done if the
148 // local log sink is in fact a Table. The way you do this is by interrogating
149 // the local sink to find out if it is in fact a TableLogSink. If it is, you
150 // can use a concatenate method of TableLogSink. Schematically this would be
151 // implemented as follows in some DataSet class that has a logSink method that
152 // returns a LogIO reference:
153 // <srcBlock>
154 // void merge(DataSet &out, const DataSet &in1, const DataSet &in2) {
155 // ... copy the data from in1 and in2 to out
156 // if (out.logSink().localSink().isTableLogSink()) { // can write to out
157 // if (in1.logSink().localSink().isTableLogSink()) {
158 // out.logSink().localSink().castToTableLogSink().concatenate(
159 // in1.logSink().localSink().castToTableLogSink());
160 // }
161 // if (... the same for in2 ...)
162 // }
163 // </srcBlock>
164 // Of course, DataSet might provide some convenience function for merging
165 // histories. However the point is that given a sink, you can safely determing
166 // whether or not it is in fact a TableLogSink, and if it is you can call
167 // its concatenate function, which takes another TableLogSink.
168 // </synopsis>
169 //
170 // <example>
171 // The following example code is checked into the system as
172 // <src>dLogging.cc</src>. It is found in the Logging test directory.
173 //
174 // <srcblock>
175 // class DataClass
176 // {
177 // public:
178 // DataClass(const IPosition &shape, const LogSink &sink); // 1
179 // void set(Int toWhat); // 2
180 // LogIO &sink() return os_p;} // 3
181 // Array<Int> &data() {return data_p;} // 4
182 // const Array<Int> &data() const {return data_p;} // 5
183 // private: // 6
184 // Vector<Int> data_p; // 7
185 // LogSink log_sink_p; // 8
186 // LogIO os_p; // 9
187 // };
188 // </srcblock>
189 //
190 // This toy class is meant to represent one which is to have "attached" logging
191 // information. Generally, these classes would be fairly high level
192 // astronomical classes, e.g. <src>Image</src>, not <src>Array</src>. Note that
193 // only operations which change the data should be logged in the internal log.
194 // Operations which only read the data should be logged either globally, or in
195 // the class that is taking the results and modifying its own data.
196 //
197 // <dl compact>
198 // <dt>1.
199 // <dd> Depending on the application, the LogSink to be used might
200 // either be handed in to the class, as is the case here, or it might
201 // be created by the class. For example, a <src>MeasurementSet</src>
202 // will have a processing log table with a known name.
203 // <dt> 2.
204 // <dd> A sample function that changes the state of the class. Here,
205 // it just sets all the elements of the internal array to
206 // <src>toWhat</src>.
207 // <dt> 3.
208 // <dd> Return the LogIO that is used by this object. A member function like this
209 // should be provided for use by global functions which manipulate the object.
210 // Note that it is non-const --- the internal sink should be modified only
211 // by functions which CHANGE the object, otherwise the global sink should be
212 // used.
213 // <dt> 4.
214 // <dd> Return the internal data. Arguably this should be logged at at least
215 // DEBUGGING level.
216 // <dt> 5.
217 // <dd> Non-const version of the above. Note that it should not be logged since
218 // the state cannot be changed with this function.
219 // <dt> 7.
220 // <dd> The internal data member.
221 // <dt> 8.
222 // <dd> The location to which log mesages are sent.
223 // <dt> 9.
224 // <dd> The LogIO object that will be the actual interface to the logging
225 // system.
226 // </dl>
227 //
228 // <srcblock>
229 // DataClass::DataClass(const IPosition &shape, const LogSink &sink)
230 // : log_sink_p(sink), os_p(log_sink_p) // 1
231 // { // 2
232 // os_p << LogOrigin("DataClass", // 3
233 // "DataClass(const IPosition &shape, const LogSink &sink)"); // 4
234 // // 5
235 // if (shape.nelements() != 1) { // 6
236 // os_p << LogIO::SEVERE << WHERE << // 7
237 // "Illegal Shape! Must be one dimensional." << LogIO::EXCEPTION; // 8
238 // } // 9
239 // // 10
240 // data_p.resize(shape(0)); // 11
241 // os_p << "Inital shape " << shape << "and value 2" << // 12
242 // LogIO::NORMAL << LogIO::POST; // 13
243 // // 14
244 // set(2); // 15
245 // }
246 // </srcblock>
247 // <dl compact>
248 // <dt> 1.
249 // <dd> The private <src>LogSink</src> data member is initialized with one that
250 // the caller provides. Note that LogSink uses reference semantics, so
251 // that if another "copy" of the sink is made then all the log messages
252 // will go to the same place. For example:
253 // <srcblock>
254 // LogSink a("mylogtable");
255 // LogSink b(a);
256 // LogSink c;
257 // c = a;
258 // ...
259 // c.post(...); // ends up in mylogtable
260 // ...
261 // b.post(...); // as does this
262 // </srcblock>
263 // This can be useful if several classes might be modifying the same data,
264 // or if a data is spread over several objects.
265 //
266 // Also, os_p is intialized from the sink.
267 // <dt> 3.
268 // <dd> For a member function, the first argument to LogOrigin is the class name.
269 // <dt> 4.
270 // <dd> The next argument is the function name. You should use the full name with
271 // arguments so that you can use the argument name in your messages. Leave
272 // off the return type. Cutting and pasting is easier than typing!
273 // <dt> 7.
274 // <dd> WHERE is a predefined macro that gives the file name and line number.
275 // <dt> 8.
276 // <dd> Create a SEVERE level error message, post it and throw an exception.
277 // <dt> 11.
278 // <dd> This will post the message locally and globally, and then throw
279 // an exception. Another possibility would be to call
280 // <src>postGloballyThenThrow()</src> if you only wanted to send the
281 // message to the global sink (for example, if the object is hopelessly
282 // corrupted, or if the problem occurs in a read-only operation). The
283 // thrown exception is an <src>AipsError</src>. The
284 // <src>post*Throw()</src> functions will always set the priority to
285 // <src>SEVERE</src>, however it doesn't hurt to show your intentions
286 // <dt> 12.
287 // <dd> Create and send a NORMAL priority message.
288 // <dt> 15.
289 // <dd> Call <src>set()</src> from the constructor to give the data values
290 // an initial value.
291 // </dl>
292 //
293 // <srcblock>
294 // void DataClass::set(Int toWhat)
295 // {
296 // os_p << LogIO::NORMAL << LogOrigin("DataClass", "set(Int toWhat)"); // 1
297 // os_p << "Setting data values to " << toWhat << WHERE << LogIO::POST; // 2
298 // uInt n = data_p.nelements(); // 3
299 // for (uInt i=0; i < n; i++) { // 4
300 // #ifdef AIPS_DEBUG // 5
301 // os_p << LogIO::DEBUGGING << WHERE << // 6
302 // "Setting element " << i << " to " << toWhat << LogIO::POST; // 7
303 // #endif // 8
304 // data_p(i) = toWhat; // 9
305 // }
306 // }
307 // </srcblock>
308 //
309 // <dl compact>
310 // <dt> 2.
311 // <dd> This and the previous line set up and send a normal priority log message
312 // much as we did previously.
313 // <dt> 7.
314 // <dd> LogMessages are relatively expensive to produces and consume. Use of
315 // them in a very tight loop should either be <src>ifdef</src>'d out as
316 // in this example, or like:
317 // <srcblock>
318 // if (aips_debug_on) {
319 // ... set up and send log message ...
320 // }
321 // </srcblock>
322 // The advantage of this code is that it's always available - so, for
323 // example, you can turn it on and off by manipulating the global variable
324 // <src>aips_debug_on</src>. However very tight loops cannot even afford
325 // this extra <src>if</src>, and should prefer the <src>ifdef</src>.
326 //
327 // Normally the <src>DEBUGGING</src> messages are "boring but low-volume",
328 // and you should just send them normally.
329 // </dl>
330 //
331 // <srcblock>
332 // void square(DataClass &object)
333 // {
334 // object.sink() << LogIO::NORMAL << WHERE << // 1
335 // LogOrigin("square(DataClass &object)") << "Squaring data elements" // 2
336 // << LogIO::POST; // 3
337 // object.data() *= object.data(); // 4
338 // }
339 // </srcblock>
340 //
341 // This function shows how a global function that modifies an object can send
342 // log messages to that objects <src>LogSink</src> using a function of that
343 // object to get access to its sink.
344 //
345 // <srcblock>
346 // float sum(const DataClass &object)
347 // {
348 // LogIO global(LogOrigin("sum(const DataClass &object)")); // 1
349 // float theSum = sum(object.data()); // 2
350 // global << WHERE << "Sum of object is: " << theSum; // 3
351 // return theSum; // 4
352 // }
353 // </srcblock>
354 // This is an example of a global function that only reads -- does not change --
355 // an object.
356 // <dl>
357 // <dt> 3.
358 // <dd> Since we are not changing the data object, we only post the message
359 // globally, we don't write it to the data object's log sink. The caller
360 // of <src>sum()</src> might log the message somewhere else if the return
361 // value is used to modify data in some other object. Instead we send it
362 // to the global sink. Here we don't POST the message ourselves, we rely
363 // on the LogIO destructor to do it for us.
364 // </dl>
365 //
366 // <srcblock>
367 // int main()
368 // {
369 // LogSink::globalSink().filter(LogMessage::DEBUGGING); // 1
370 // LogSink logger(LogMessage::NORMAL, "dLogging_messages_tmp"); // 2
371 // // 3
372 // IPosition legalShape(1, 10); // 4
373 // DataClass dc(legalShape, logger); // 5
374 // // 6
375 // square(dc); // 7
376 // // 8
377 // Float total = sum(dc); // 9
378 // // 10
379 // return 0; // 11
380 // }
381 // </srcblock>
382 // <dl compact>
383 // <dt> 1.
384 // <dd> Change the priority of messages to display on the global sink's
385 // filter to
386 // <src>DEBUGGING</src> from the default <src>NORMAL</src>. The default
387 // global sink logs to cerr. The global sink can be replaced with
388 // <src>LogSink::globalSink()</src>.
389 // <dt> 2.
390 // <dd> Create the sink that we are going to use. This constructor will use
391 // a <linkto class="Table">Table</linkto>. If the table doesn't exist
392 // it will be created. If it does exist, new log messages will be appended
393 // to the end.
394 // <dt> 5.
395 // <dd> Create an object with the provided sink. The alternative strategy, which
396 // will be used with classes like
397 // <linkto class="MeasurementSet">MeasurementSet</linkto> is for the object
398 // to make it's own <src>LogSink</src> if it knows where it wants its
399 // messages to go.
400 // <dt> 7.
401 // <dd> Changes the data - log messages go to its local sink.
402 // <dt> 9.
403 // <dd> Reads the data - log messages go only to the global sink.
404 // </dl>
405 
406 // </example>
407 //
408 // <motivation>
409 // <ol>
410 // <li> Attaching informational messages to datasets to describe their processing
411 // history.
412 // <li> Informational messages to inform the user about the progress and
413 // parameters of algorithms - for example those used for reference frame
414 // conversions in the Measures module.
415 // </ol>
416 // </motivation>
417 
418 // <todo asof="1997/01/19">
419 // <li> More filtering options?
420 // </todo>
421 
422 // </module>
423 
424 
425 } //# NAMESPACE CASACORE - END
426 
427 #endif
#define casacore
&lt;X11/Intrinsic.h&gt; #defines true, false, casacore::Bool, and String.
Definition: X11Intrinsic.h:42