1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
|
<!-- $Id$ -->
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="GENERATOR" content="Mozilla/4.5 [en] (WinNT; I) [Netscape]">
<title>Configuring TAO's Components</title>
</head>
<body text="#000000" bgcolor="#FFFFFF" link="#000FFF" vlink="#FF0F0F">
<hr>
<h3>
Configuring TAO's Components</h3>
<h3> Overview</h3>
<p> As described in the <a href="Options.html">options</a>
documentation, various components in TAO can be customized by
specifying options for those components. This document illustrates
how to combine these options in order to affect ORB behavior and
performance, particularly its <a
href="http://www.cs.wustl.edu/~schmidt/CACM-arch.ps.gz">concurrency
model</a>. </p>
<p> TAO configures itself using the <a
href="http://www.cs.wustl.edu/~schmidt/Svc-Conf.ps.gz">ACE
Service Configurator</a> framework. Thus, options are specified in the
familiar <tt>svc.conf</tt> file (if you want to use a different file
name, use the <tt><a href="Options.html#svcfonf">-ORBsvcconf</a></tt>
option). You can also setup default configurations for your programs.
Please see the <a href="#programming">Programming Considerations</a>
for more detailed discussion on this.</p>
<hr>
<h3>
Roadmap</h3>
<blockquote>Details for the following configurations are provided.
<ul>
<li>
<b><a href="#comp">Configurating key components</a>:</b></li>
<ul>
<li>
<a href="#concurrency">Server Concurrency Strategy.</a></li>
<li>
<a href="#orb">ORB and other resources.</a></li>
<li>
<a href="#poa">POA.</a></li>
<li>
<a href="#coltbl">Collocation Table.</a></li>
<li>
<a href="#iiopprofile">Forwarding IIOP Profile</a></li>
<li>
<a href="#orbsvcs">orbsvcs Library</a></li>
</ul>
<li>
<b><a href="#examples">Configuration examples</a></b></li>
<ul>
<li>
<a href="#reactive">Single-threaded, reactive model.</a></li>
<li>
<a href="#tpc">Multiple threads, thread-per-connection model.</a></li>
<li>
<a href="#multiorb">Multiple threads, ORB-per-Reactor-thread model.</a></li>
<li>
<a href="#multiorb-tpc">Multiple threads, ORB-per-thread, thread-per-connection
model.</a></li>
<li>
<a href="#tpool">Multiple threads, thread-pool model.</a> (Not yet implemented.)</li>
<li>
<a href="#multiorb-tpool">Multiple threads, ORB-per-thread, thread-pool
model.</a> (Not yet implemented.)</li>
<li>
Each configuration has the following information:</li>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="70%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>A brief description of the scenario and its typical use.</td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>The number of threads used by ORB-related activities.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>Identifies the creator of the threads discussed above.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Where information on various resources is stored.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>Describes what task is undertaken for each thread.</td>
</tr>
<tr ALIGN=LEFT>
<th>Options</th>
<td>Specifies the options for each service in order to utilize this configuration.</td>
</tr>
</table>
</ul>
<li>
<b><a href="#programming">Programming considerations</a></b>
<li>
<b><a href="#homogenous">Configuration for homogenous systems</a></b></li>
<ul>
<li>
<a href="#homogenous_compile">Compile time options</a></li>
<li>
<a href="#homogenous_runtime">Runtime time</a></li>
</ul>
</ul>
</blockquote>
<hr>
<h3>
<a NAME="comp"></a>Configuring key components</h3>
<ul>
<li>
<a NAME="concurrency"></a><b>Server concurrency strategy</b> specifies
the concurrency strategy an ORB uses. It says nothing about how many ORBs
(or, threads) are there in a process.</li><P>
<ul>
<li>
<tt>reactive</tt>: The ORB handles requests reactively, i.e., the ORB runs
in one thread and service multiple requests/connections simultaneously
using "<tt>select</tt>" call. You can have multiple ORBs accepting requests
reactively and running in separate threads.</li>
<li>
<tt>thread-per-connection</tt>: The ORB handles new connections by spawning
a new thread whose job is to service requests coming from the connection.
The new threads inherits all properties from the ORB threads (see below.)</li>
<li>
<tt>thread-pool</tt> (not yet implemented): ... to be continued ...</li>
</UL><P>
<li>
<a NAME="orb"></a><b>ORB and other resources.</b></li><P>
<ul>
<li>
<tt>global</tt>: There's only one ORB process-wide. <tt>ORB_init () </tt>must
be called only once. Every thread accesses the same ORB.</li>
<li>
<tt>tss</tt>: When using <tt>tss</tt> ORB, the programmer is responsible
for spawning the ORB threads and setting up the ORB by calling <tt>ORB_init
()</tt> for each ORB threads. Any ORB spawned thread (i.e., thru thread-per-connection)
shares the same resource the spawning ORB uses.</li>
</ul><P>
<li>
<a NAME="poa"></a><b>POA.</b></li><P>
<ul>
<li>
<tt>global</tt>: All ORBs share the same POA. The advantage of using a
global POA is that once an object is registered to the POA under an ORB,
it can be externalized from other ORB.</li>
<li>
per ORB (<tt>tss</tt>): Each ORB has its own POA, which means, the programmer
should also instantiate the POA for each ORB (otherwise, a default RootPOA
gets created, which might not be what you what and thus, is discouraged.)</li>
</ul><P>
<li>
<a NAME="coltbl"></a><b>Collocation Table:</b> Care must be
taken when using CORBA objects to control the ORB directly. For you are
actually executing the collocated object, not in the object's ORB context,
but in the calling ORB's context.</li><P>
<ul>
<li>
<tt>global</tt>: Process keeps a global collocation table which contains
tuples of listening endpoint and its corresponding RootPOA.</li><P>
<li>
per ORB (<tt>tss</tt>): At this moment, since TAO only supports one listening
endpoint per ORB, there is no per-ORB collocation Table. Checking of collocated
objects is done by comparing object's IIOP profile and the calling ORB's
listening endpoint.</li><P>
</ul>
<li>
<a NAME="iiopprofile"></a><b>Forwarding IIOP Profile:</b> In the case of
multiple threads using the same <tt>CORBA::Object</tt> and using forwarding,
it is necessary to protect the forwarding <tt>IIOP_Profile</tt>, which
is part of the <tt>IIOP_Object</tt>, which is part of the CORBA::Object
against multiple access. Therefore a mutex lock is used by default to ensure
proper access. Using the switch <tt>-ORBiiopprofilelock</tt> this policy
can be deactivated specifying <tt>-ORBiiopprofilelock null</tt>. A motivation
to do this might be performance reasons in cases, where no forwarding is
used or no multithreading with access to shared <tt>CORBA::Object</tt>'s.
Deactivating forces the ORB to use a null mutex, which does introduce only
a very small overhead, compared with overhead introduced by a regular mutex
lock.</li><P>
<li>
<a NAME="orbsvcs"></a><b>orbsvcs Library:</b> By default, the TAO orbsvcs
library contains all of the services that TAO currently supports. To reduce
build time and library size, you can exclude unused services. To do that,
define a <tt>TAO_ORBSVCS</tt> variable using one of these approaches:</li><P>
<ol>
<li>In your <tt>$(ACE_ROOT)/include/makeinclude/platform_macros.GNU</tt>
file,<p>
<li>On the make command line, <i>e.g.</i>,
<tt>make TAO_ORBSVCS=Event</tt>, or<p>
<li>Set (and export) a <tt>TAO_ORBSVCS</tt> environment variable.
</ol><p>
Please see the <code><a href="../orbsvcs/orbsvcs/Makefile">ORBSVCS
Makefile</a></code> for the default setting of <code>TAO_ORBSVCS</code>.<p>
Please note that the Naming Service will always be built, even
if Naming is not specified in <code>TAO_ORBSVCS</code>. That's
because many examples, tests, and presumably applications use it.<p>
</ul>
<hr>
<h3>
<a NAME="examples"></a>Configuration Examples</h3>
The following are common ORB configurations used by TAO applications.<P>
<ul>
<li>
<a NAME="reactive"></a>Single-threaded, reactive model.</li><P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr>
<th ALIGN=LEFT>Typical Use</th>
<td>This is the default configuration of TAO, where one thread handles
requests from multiple clients via a single Reactor. It is appropriate
when the requests (1) take a fixed, relatively uniform amount of time and
(2) are largely compute bound. </td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>1</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>OS or whomever creates the main ORB thread in a process.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Resources are stored process-wide.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>The single thread processes all connection requests and CORBA messages.</td>
</tr>
<tr ALIGN=LEFT>
<th>Options</th>
<td><tt>TAO_Resource_Manager</tt>: <tt>-ORBresources global</tt>
<br><tt>TAO_Server_Strategy_Factory</tt>: <tt>-ORBconcurrency reactive</tt></td>
</tr>
</table>
<P>Check out the <tt><a
href="../tests/Param_Test/">Param_Test</a></tt> for
an example of this configuration. <P>
<li>
<a NAME="tpc"></a>Multiple threads, thread-per-connection model.</li> <P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>This configuration spawns a new thread to serve requests from a new
connection. This approach works well when there are multiple connections
active simultaneously and each request-per-connection may take a fair amount
of time to execute.</td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>1 plus the number of connections.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>Programmer must set up the main thread which is responsible to create
new threads for new connections.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Process-wise.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>The main thread handles new connections and spawns new threads for
them. Other threads handle requests for established connections.</td>
</tr>
<tr ALIGN=LEFT>
<th>Options</th>
<td><tt>TAO_Resource_Manager</tt>: <tt>-ORBresources global</tt>
<br><tt>TAO_Server_Strategy_Factory</tt>: <tt>-ORBconcurrency thread-per-connection</tt></td>
</tr>
</table>
<P>
<tt><a href="../performance-tests/Cubit/TAO/IDL_Cubit/">IDL_Cubit</a></tt>
is a good example on using <i>multiple threads, thread-per-connection</i>
configuration.<P>
<li>
<P>Multiple threads, ORB-per-thread model.<a NAME="multiorb"></a></li><P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>In this configuration, there multiple ORBs per process each
running in its own thread. Each thread handles requests
reactively. It's good for hard real-time applications that require
different thread priorities for the various ORBs.</td> </tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>The number of ORBs.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>The main process (thread).</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Thread specific.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>Service the requests from associating ORB.</td>
</tr>
<tr ALIGN=LEFT>
<th>Options</th>
<td><tt>TAO_Resource_Manager</tt>: <tt>-ORBresources tss</tt>
<br><tt>TAO_Server_Strategy_Factory</tt>: <tt>-ORBconcurrency reactive</tt></td>
</tr>
</table>
<P>
<li>
Multiple threads, ORB-per-thread, thread-per-connection model.<a NAME="multiorb-tpc"></a></li><P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>This approach provides a range of thread priorities plus connections
that don't interfere with each others.</td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>Number of ORBs plus number of connections.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>Main threads creates threads running ORBs. They, in turns, create connection
handling threads.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Thread specific.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>There are ORB threads which handle connection requests and handler
threads which service requests form establiched connections.</td>
</tr>
<tr ALIGN=LEFT>
<th>Options</th>
<td><tt>TAO_Resource_Manager</tt>: <tt>-ORBresources tss</tt>
<br><tt>TAO_Server_Strategy_Factory</tt>: <tt>-ORBconcurrency thread-per-connection</tt></td>
</tr>
</table>
<P>
<tt><a href="../performance-tests/Cubit/TAO/MT_Cubit/">MT_Cubit</a></tt>
is a good example on using <i>multiple threads, ORB-per-thread, and thread-per-connection</i>
configuration.<P>
<li>
<a NAME="tpool"></a>Multiple threads, thread-pool model. (Not yet implemented.)</li><P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>This model implements a highly optimized thread pool that minimizes
context switching, synchronization, dynamic memory allocations, and data
movement between threads.</td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>The number of threads used by ORB-related activities.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>Identifies the creator of the threads discussed above.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Where information on various resources is stored.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>Describes what task is undertaken for each thread.</td>
</tr>
</table>
<P><li>
Multiple threads, ORB-per-thread, thread-pool model.<a NAME="multiorb-tpool"></a>
(Not yet implemented.)</li><P>
<table BORDER=2 CELLSPACING=2 CELLPADDING=0 WIDTH="90%" >
<tr ALIGN=LEFT>
<th>Typical Use</th>
<td>A brief description of the scenario and its typical use.</td>
</tr>
<tr ALIGN=LEFT>
<th>Number of Threads</th>
<td>The number of threads used by ORB-related activities.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread Creator</th>
<td>Identifies the creator of the threads discussed above.</td>
</tr>
<tr ALIGN=LEFT>
<th>Resource Location</th>
<td>Where information on various resources is stored.</td>
</tr>
<tr ALIGN=LEFT>
<th>Thread task</th>
<td>Describes what task is undertaken for each thread.</td>
</tr>
</table>
</ul>
<hr>
<h3>
Programming Considerations<a NAME="programming"></a></h3>
There are several ways to pass option flags into TAO's
components. <P>
<ul>
<li><p>The plain vanilla approach is do nothing. All TAO components
use their default settings as described in <a
href="Options.html">this document</a>.</p>
<li><p>The most common use case is to use a file called
<code>svc.conf</code>. On most platforms, TAO programs
automatically search and read in the file. The disadvantage of
this approach is you always need a <code>svc.conf</code> file if
you want to do use non-default configuration.</p>
<li><p>You can use <code>-ORBsvcconf <em>filename</em></code> to use
a config file that is not called <code>svc.conf</code>.
Specifying <code>-ORBsvcconf</code> exclude the reading of
default <code>svc.conf</code> file.</p>
<li><p>If you don't want the application users to worry about
setting up or knowing about <code>svc.conf</code> files, you can
call <code>TAO_Internal::default_svc_conf_entries()</code>
before calling the first <code>ORB_init()</code> in your program
to set up the default svc.conf entries. In this case, if a TAO
application cannot find a svc.conf file, it will configure TAO's
components using the default settings. You can still use a
<code>svc.conf</code> file or use <code>-ORBsvcconf</code>
option to tune the program.<P>
<li><p>TAO programs evaluate the configuration settings in the following
order,</p>
<ul>
<li>File specified in <code>-ORBsvcconf</code> command-line
option, if one exist. Otherwise, the
<code>svc.conf</code> in the start-up directory will be
evaluated, if one exist.
<li>Default entries set by
<code>TAO_Internal::default_svc_conf_entries()</code>, if
ones exist.
<li>Default configuration as specified in <a
href="Options.html">this document</a>.
</ul>
<p>Notice that the first encountered component settings are
always the ones take effect. For example, if you set the entries
for <code>Resource_Factory</code> and
<code>Server_Strategy_Factory</code> using
<code>TAO_Internal::default_svc_conf_entries()</code> in a
program and you also have a file called <code>svc.conf</code>
which has an entry for <code>Resource_Factory</code>. This
program will use the entry for <code>Resource_Factory</code> in
the <code>svc.conf</code> file, the entry for
<code>Server_Strategy_Factory</code> set in the program, and the
in-stock <code>Client_Strategy_Factory</code> that TAO defines.
<li><p>Some platforms do not support reading of <code>svc.conf</code>
files or you would rather not to use the feature. In this case,
you must define <code>TAO_PLATFORM_SVC_CONF_FILE_NOTSUP</code>
in your ACE <code>config.h</code> file and recompile TAO
library. In this case, a TAO program will not try to search for
the default <code>svc.conf</code> file. However, if platform
support, you can still use <code>-ORBsvcconf</code> to change
the program behavior temporarily.</p>
<p>On these platform, you can alter the default settings for
TAO components by defining the following macros in your
<code>config.h</code> file:</p>
<ul>
<li><code>TAO_DEFAULT_RESOURCE_FACTORY_ARGS</code>
<li><code>TAO_DEFAULT_SERVER_STRATEGY_FACTORY_ARGS</code>
<li><code>TAO_DEFAULT_CLIENT_STRATEGY_FACTORY_ARGS</code>
</ul>
<p>The ACE Makefiles <code>fakesvcconf</code> flag can be
used to define <code>TAO_PLATFORM_SVC_CONF_FILE_NOTSUP</code>.
To define that macro, just add <code>fakesvcconf=1</code> to
your <code>make</code> invocation.
<p>See <a href="../tao/orbconf.h"><code>orbconf.h</code></a> for
an example.
</ul>
<hr>
<h3>
Configuration for homogenous systems<a NAME="homogenous"></a></h3>
<ul>
<LI><b>Compile-time options</b><a NAME="homogenous_compile"></a>
<p>Many real-time applications run on homogenous environments, TAO (and
ACE) can take advantage of this fact by simplifying the server side demarshaling;
to enable this feature you have to edit the <tt>$ACE_ROOT/ace/OS.h</tt>
file and enable the macro <font size=-1>ACE</font><tt>_DISABLE_SWAP_ON_READ</tt>.
<p>In this systems it is also common that server and the client startup
and shutdown simultaneously, in those circumstances there is no need to
check the timestamps in the POA, another macro (<tt>POA_NO_TIMESTAMP</tt>)
can be used for this purpose.
<p>Users running in embebbed systems may also need to modify the default
options for TAO, the macros <tt>TAO_DEFAULT_RESOURCE_FACTORY_ARGS</tt>,
<tt>TAO_DEFAULT_CLIENT_STRATEGY_FACTORY_ARGS</tt> and <tt>TAO_DEFAULT_SERVER_STRATEGY_FACTORY_ARGS</tt>
can be used for those purposes. If the footprint size is an issue users
may consider writing custom strategy factories that only create the right
strategies, this eliminates the parsing code for the different options.
<p>
<LI><b>Run-time options</b><a NAME="homogenous_runtime"></a>
<p>If the only ORB running is TAO and there is no need to be IIOP interoperable
the option <tt>-ORBgioplite</tt> can be used to reduce the message size
and the processing time.
<p>Some embedded systems run without the benefit of a DNS server, in that
case they can use the <tt>-ORBdotteddecimaladdresses</tt> option; the ORB
will avoid the use of hostnames in the profiles it generates, thus clients
don't need to do any name resolution. The compile-time define <tt>TAO_USES_DOTTED_DECIMAL_ADDRESSES</tt>
in <tt>$TAO_ROOT/tao/orbconf.h</tt> to make this the default behavior.</ul>
<hr>
<h3>Hints</h3>
Choosing the right configuration is hard and, of course, depends on your
application. In the following section we will attempt to describe some
motivations for features in TAO, hopefully that can guide you through the
choice of your configuration options.
<ul>
<LI><b>ORB-per-thread</b> The main motivation behind this options is to
minimize priority invertion, since threads share no ORB resources no locking
is required and thus, priority is preserved in most cases (assuming proper
support from the OS). If you are not too concerned about priority inversion
try to use a global ORB, using ORB-per-thread has some tradeoffs (like
calling ORB_init on each thread, activation of a servant is more complicated,
etc.) Some of the problems, can be minimized, but they require even more
careful analysis. For example, object activation can be simplified by using
a global POA; the careful reader will wonder how could global POA be useful
in anyway since it will require locks and thus introduce priority inversions
again; some applications activate all their objects beforehand so locks
in the POA are not always needed; other applications only activate a few
objects after startup, so they can use a child POA with the right locking
policy for the dynamic servants and the root poa (with no locking) for
the majority of the servants.
<p>As the reader will note this is a delicate configuration option, the
rule of thumb should be <b>not</b> to use ORB-per-thread unless it is really
required. <P>
<li>
<b>Collocation tables</b> Why could the application what a non-global
collocation table? If objects are to serve requests only at a well
known priority the application can be configured with the
ORB-per-thread option, and the object is activated only in the thread
(ORB) corresponding to the desired priority. But using a global table
would subert the priority assignment (because calls would run at the
priority of the client).</li><P>
<li> <b>Single-threaded vs. Multi-threaded Connection Handlers</b> The
<tt>Client_Connection_Handler</tt> is the component in TAO that writes
the requests to the underlying transport socket; this is also the
component that reads the response back from the server.</li>
<p>
While waiting for this response new requests to the local ORB can
arrive, this is the so-called nested upcall support. TAO supports two
mechanisms for handling nested upcalls, the default uses the
leader-follower model to allow multiple threads to wait on a single
reactor for several concurrent requests; sometimes this configuration
can be an overkill, if only one thread is using a reactor at the same
time a lighter weight implementation can be used. <p>This
configuration is controled by the <tt>-ORBclientconnectionhandler</tt>
option, good opportunities to use this option are:<P>
<ul> <li> Single
threaded servers</li>
<li>
Servers running in ORB-per-thread mode</li>
<li>
Pure clients that will never receive a request</li>
</ul><P>
<li>
<b>Allocator for input CDR streams</b> Normally the application has no
access to this buffer, and it is only used on the demarshaling of arguments
(or results). It is almost always better to use the "<tt>-ORBinputcdrallocator
null</tt>" option since it will allocate memory from a thread specific allocator
and it will not need locks to manage that memory.</li>
<p>In some cases the user <i>may</i> gain access to the CDR stream
buffer: TAO makes no copies when demarshaling octet sequences, instead
the octet sequence simply points to the CDR buffer, since the octet
sequence does not own this buffer a copy must be made if the user
wants to keep the buffer after the upcall.
<p>The user can, however, increase the reference count on the CDR
stream buffer, thus allowing her to extend the lifetime of this
buffer. Still passing this buffer to another thread and attempting to
release it in that thread will result in some memory leak or
corruption. Users willing to use this feature of TAO can still do so,
<b>if</b> they use a global allocator for their input CDR stream, but
that will introduce extra locking on the critical path. <p>As the
reader can see this is an option that has limited applicability and
requires careful consideration of the tradeoffs involved.</ul>
<hr>
<p>Back to the TAO <a href="components.html">components documentation</a>.<!--#include virtual="/~schmidt/cgi-sig.html" -->
</body>
</html>
|
