TAO/docs/releasenotes/trader.html

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  12 <h1 align="center">TAO Trading Service Documentation</h1>
  13
  14 <hr>
  15
  16 <p>The TAO transient Trading Service implements the COS TradingObject Service
  17 specification, and&nbsp; conforms to the Linked Trader conformance criteria. This document
  18 details how to use the TAO Trading Service from the following perspectives:
  19
  20 <ul>
  21   <li>as an importer bootstrapping to the Trading Service;</li>
  22   <li>as a service offer exporter;</li>
  23   <li>as an administrator;</li>
  24   <li>as an out-of-the-box server process; </li>
  25   <li>as a collocated object. </li>
  26 </ul>
  27
  28 <p>In addition, it covers running the Trading Service tests and discusses known bugs and
  29 workarounds.</p>
  30
  31 <p>This document assumes you are familiar with Trading Service concepts, such as
  32 &quot;importer,&quot; &quot;exporter&quot;, &quot;service type&quot;, &quot;service
  33 offer,&quot; and &quot;dynamic property&quot;, as well as the roles of each of the Trading
  34 Service's interfaces --- <tt>Lookup</tt>, <tt>Register</tt>, <tt>Admin</tt>, and <tt>Link</tt>
  35 (the TAO implementation doesn't currently support <tt>Proxy</tt>). I recommend reading the
  36 first two sections of the <a href="ftp://www.omg.org/pub/docs/formal/97-12-23.pdf">Trading
  37 Service specification</a>. This document has the following layout:
  38
  39 <ol>
  40   <li><a href="#TheClientRole">The Client Role</a> <ul>
  41       <li><a href="#BootstrappingtotheTradingService">Bootstrapping to the Trading Service</a> </li>
  42       <li><a href="#The ImporterRolePerformingaQuery">The Importer Role --- Performing a Query</a><ul>
  43           <li><a href="#Constraints">Constraints</a></li>
  44           <li><a href="#Preferences">Preferences</a></li>
  45           <li><a href="#Policies">Policies</a></li>
  46           <li><a href="#FilteringProperties">Filtering Properties</a> </li>
  47           <li><a href="#OfferIterators">Offer Iterators</a></li>
  48           <li><a href="#PropertyEvaluation">Property Evaluation</a></li>
  49         </ul>
  50       </li>
  51       <li><a href="#TheExporterRole">The Exporter Role --- Registering a Service Type and Offer</a>
  52         <ul>
  53           <li><a href="#TheServiceTypeRepository">The Service Type Repository</a> </li>
  54           <li><a href="#ExportingWithdrawingandModifying">Exporting, Withdrawing, and Modifying
  55             Service Offers</a> </li>
  56           <li><a href="#ImplementingDynamicProperties">Implementing Dynamic Properties</a></li>
  57         </ul>
  58       </li>
  59       <li><a href="#TheAdministratorRole">The Administrator Role --- Tweaking Policies and
  60         Adjusting Links</a></li>
  61     </ul>
  62   </li>
  63   <li><a href="#TheServerRole">The Server Role</a><ul>
  64       <li><a href="#TheTAOTradingServiceApplication">The TAO <tt>Trading_Service</tt> Application</a></li>
  65       <li><a href="#ColocatingtheTradingServiceinaTAOApplication">Colocating the Trading Service
  66         in a TAO Application</a></li>
  67     </ul>
  68   </li>
  69   <li><a href="#RunningtheTradingServiceTests">Running the Trading Service Tests</a></li>
  70   <li><a href="#KnownBugsandWorkarounds">Known Bugs and Workarounds</a></li>
  71   <li><a href="#FutureWork">Future Work</a></li>
  72 </ol>
  73
  74 <hr>
  75
  76 <h1><a name="TheClientRole">The Client Role</a></h1>
  77
  78 <p align="left">There are three categories of operations that a client can perform on a
  79 Trading Service instance: exporting a service offer to the Trading Service, importing a
  80 list of Service Offers whose properties satisfy a constraint expression, and attending to
  81 administrative duties --- tweaking policies or adjusting links. The first order of
  82 business, of course, is obtaining a reference to a Trading Service instance, assuming that
  83 instance is not colocated with the client. </p>
  84
  85 <h2 align="left"><a name="BootstrappingtotheTradingService">Bootstrapping to the Trading
  86 Service</a></h2>
  87
  88 <p align="left">Like with the Naming Service, the ORB will obtain a reference to a Trading
  89 Service instance's <tt>Lookup</tt> interface when a client invokes the <tt>CORBA::ORB::resolve_initial_references</tt>
  90 method and passes to it the <tt>ObjectID</tt> &quot;<tt>TradingService</tt>&quot;. The
  91 following TAO code bootstraps to the Trading Service:</p>
  92
  93 <table border="1" width="100%" cellpadding="6">
  94   <tr>
  95     <td width="100%"><pre>
  96 {
  97   TAO_ORB_Manager orb_manager;
  98   orb_manager.init (argc, argv, );
  99   CORBA::ORB_var orb = orb_manager.orb ();
 100   CORBA::Object_var trading_obj =
 101     orb-&gt;resolve_initial_references ("TradingService");
 102   CosTrading::Lookup_var lookup_if =
 103     CosTrading::Lookup::_narrow (trading_obj.in ());
 104 }
 105 catch (const CORBA::Exception& ex)
 106 {
 107   ex.print_exception (&quot;Failed to bootstrap to a trader&quot;);
 108 }
 109 </pre>
 110     </td>
 111   </tr>
 112 </table>
 113
 114 <p>The first time <tt>resolve_initial_references</tt> is called, the ORB uses a multicast
 115 protocol to locate an existing trader. The ORB emits a multicast packet containing a field
 116 identifying the desired service --- Naming or Trading --- and the port number that the
 117 client is listening on for the response (the IP address can be inferred from the packet).
 118 When the trader receives the packet and finds that the id contained within matches its
 119 own, it opens a socket to the client on the designated port, and sends its IOR, which the
 120 ORB converts to an object reference that it caches. </p>
 121
 122 <p>If the trader IOR is known ahead of time, the string can be passed to the client in the
 123 environment variable <tt>TradingService</tt>, or by the command line option <tt>-ORBtradingserviceior
 124 &lt;IOR&gt;</tt>. Likewise, if the multicast port is known ahead of time and differs from
 125 the default port, the port number can be passed to the client in the environment variable <tt>TradingServicePort</tt>,
 126 or by the command line option <tt>-ORBtradingserviceport &lt;PORTNUM&gt;</tt>. &nbsp; </p>
 127
 128 <h2><a name="The ImporterRolePerformingaQuery">The Importer Role --- Performing a Query</a></h2>
 129
 130 <p>Once the importer has obtained a reference to a trader's <tt>Lookup</tt> interface, it
 131 next needs to fire up a query. The query method takes nine parameters (aside from the <tt>CORBA::Environment</tt>):</p>
 132
 133 <table border="1" width="100%" cellpadding="3">
 134   <tr>
 135     <td width="39%"><tt>const CosTrading::ServiceTypeName</tt></td>
 136     <td width="61%">The Trading Service will search Offers belonging to this subtype. If the <tt>exact_type_match</tt>
 137     policy wasn't explicitly set to false, then offers belonging to subtypes of this type will
 138     also be searched. </td>
 139   </tr>
 140   <tr>
 141     <td width="39%"><tt>const CosTrading::Constraint</tt></td>
 142     <td width="61%">An expression in the OMG standard constraint language, where each property
 143     name is a property defined in the Service Type description of the type being searched.</td>
 144   </tr>
 145   <tr>
 146     <td width="39%"><tt>const CosTrading::Lookup::Preference</tt></td>
 147     <td width="61%">An expression in the OMG standard constraint language dictating how offers
 148     in the <tt>returned_offers</tt> sequence should be ordered.</td>
 149   </tr>
 150   <tr>
 151     <td width="39%"><tt>const CosTrading::PolicySeq</tt></td>
 152     <td width="61%">Policies governing the breadth of search and the type of permissible
 153     offers. A policy is a name/value pair --- a string and an <tt>Any</tt> --- that affect the
 154     search algorithm. </td>
 155   </tr>
 156   <tr>
 157     <td width="39%"><tt>const CosTrading::Lookup::SpecifiedProps</tt></td>
 158     <td width="61%">A union specifying which properties should be returned in each offer. If
 159     the descriminator is <tt>CosTrading::Lookup::some</tt>, the union&nbsp; contains the list
 160     of designated property names. Other options are <tt>all</tt>or <tt>none</tt>. </td>
 161   </tr>
 162   <tr>
 163     <td width="39%"><tt>CORBA::ULong how_many</tt></td>
 164     <td width="61%">The number of offers that should be placed in the returned sequence.</td>
 165   </tr>
 166   <tr>
 167     <td width="39%"><tt>CosTrading::OfferSeq_out</tt></td>
 168     <td width="61%">A list of ordered offers whose properties meet the constraints.</td>
 169   </tr>
 170   <tr>
 171     <td width="39%"><tt>CosTrading::OfferIterator_out</tt></td>
 172     <td width="61%">Iterator over returned offers in excess of how_many --- unordered.</td>
 173   </tr>
 174   <tr>
 175     <td width="39%"><tt>CosTrading::PolicyNameSeq_out</tt></td>
 176     <td width="61%">A sequence of policy names for policies that limited the search.</td>
 177   </tr>
 178 </table>
 179
 180 <h3><a name="Constraints">Constraints</a></h3>
 181
 182 <p>A constraint is a string in the OMG standard constraint language (the BNF can be found
 183 at the end of the specification). The trader iterates over applicable offers, and for each
 184 offer determines if its properties meet the constraints, replacing property names in the
 185 string with their values and computing the result. If the constraint evaluates to true,
 186 the offer is placed in the pool of matched offers. If the constraint string is
 187 syntactically invalid, contains property names not found in the service type description
 188 for the listed service type, or has operators with mismatched operand types, the query
 189 method will throw an <tt>InvalidConstraint</tt> exception. </p>
 190
 191 <p>Operands can be of two types: property names or literals. A property name is an
 192 unquoted string of alphanumeric characters and underscores that begins with a letter. The
 193 service type describes the type of a property. A literal is an signed or unsigned integer,
 194 floating point number --- scientific notation acceptable ---, single-quoted string, or
 195 boolean --- written TRUE or FALSE. </p>
 196
 197 <p>The constraint language supports the following operations:</p>
 198
 199 <table border="1" width="100%" cellpadding="3">
 200   <tr>
 201     <td width="25%">Arithmetic (+, -, *, /)</td>
 202     <td width="34%"><tt>Disk_Space*1000 - Amount_Used/10</tt></td>
 203     <td width="41%">Accepts two numeric operands.</td>
 204   </tr>
 205   <tr>
 206     <td width="25%">Inequality (&lt;,&gt;,&lt;=,&gt;=)</td>
 207     <td width="34%"><tt>Amount_Used &lt; Disk_Space</tt></td>
 208     <td width="41%">Accepts two numeric or two string operands.</td>
 209   </tr>
 210   <tr>
 211     <td width="25%">Equality (==, !=)</td>
 212     <td width="34%"><tt>Amount_Used == Disk_Space</tt></td>
 213     <td width="41%">Accepts two numeric, two string, or two boolean operands.</td>
 214   </tr>
 215   <tr>
 216     <td width="25%">Substring (~)</td>
 217     <td width="34%"><tt>'.wustl.edu' ~ Domain_Name</tt></td>
 218     <td width="41%">Accept two string operands. Returns true if the right string contains the
 219     left.</td>
 220   </tr>
 221   <tr>
 222     <td width="25%">Sequence inclusion (in)</td>
 223     <td width="34%"><tt>'sbw1' in User_Queue</tt></td>
 224     <td width="41%">Accepts an operand of a primitive CORBA type on the left, and a sequence
 225     of the same type on the right. Returns true when the sequence contains the value in the
 226     left operand, false otherwise.</td>
 227   </tr>
 228   <tr>
 229     <td width="25%">Property existence (exist)</td>
 230     <td width="34%"><tt>exist User_Queue</tt></td>
 231     <td width="41%">Accepts a property name. Returns true if the property is defined in the
 232     offer.</td>
 233   </tr>
 234 </table>
 235
 236 <h3><a name="Preferences">Preferences</a></h3>
 237
 238 <p>A preference is a constraint language string that determines the order of offers in the
 239 returned offer sequence. There are five types of preferences:</p>
 240
 241 <table border="1" width="100%" cellpadding="3">
 242   <tr>
 243     <td width="18%"><tt>min</tt> &lt;expression&gt;</td>
 244     <td width="82%">Offers are ordered by ascending expression value. The expression must
 245     return a number.</td>
 246   </tr>
 247   <tr>
 248     <td width="18%"><tt>max</tt> &lt;expression&gt; </td>
 249     <td width="82%">Offers are ordered by descending expression value. The expression must
 250     return a number. </td>
 251   </tr>
 252   <tr>
 253     <td width="18%"><tt>with</tt> &lt;expression&gt;</td>
 254     <td width="82%">Offers are partitioned into two parts: those offers for which the
 255     expression returns true are placed in the front, the rest in the back. The expression must
 256     return a boolean value.</td>
 257   </tr>
 258   <tr>
 259     <td width="18%"><tt>random</tt></td>
 260     <td width="82%">Offers in the sequence are shuffled.</td>
 261   </tr>
 262   <tr>
 263     <td width="18%"><tt>first</tt></td>
 264     <td width="82%">Offers are placed in the sequence in the order they're evaluated.</td>
 265   </tr>
 266 </table>
 267
 268 <h3><a name="Policies">Policies</a></h3>
 269
 270 <p>The following import policies are descibed in the specification and supported by the
 271 TAO Trading Service:</p>
 272
 273 <table border="1" width="100%" cellpadding="3">
 274   <tr>
 275     <td width="22%"><tt>exact_type_match</tt></td>
 276     <td width="18%"><tt>CORBA::Boolean</tt></td>
 277     <td width="60%">True --- Search only considers offers belonging to&nbsp; the given type.<br>
 278     False --- Search considers offers belonging to the given type or any of its subtypes.</td>
 279   </tr>
 280   <tr>
 281     <td width="22%"><tt>search_card</tt></td>
 282     <td width="18%"><tt>CORBA::ULong</tt></td>
 283     <td width="60%">Search ceases after <tt>search_card</tt> number of offers have been
 284     evaluated.</td>
 285   </tr>
 286   <tr>
 287     <td width="22%"><tt>match_card</tt></td>
 288     <td width="18%"><tt>CORBA::ULong</tt></td>
 289     <td width="60%">Search ceases after <tt>search_card</tt> number of offers have been
 290     matched.</td>
 291   </tr>
 292   <tr>
 293     <td width="22%"><tt>return_card</tt></td>
 294     <td width="18%"><tt>CORBA::ULong</tt></td>
 295     <td width="60%">Query returns at most <tt>return_card</tt> number of offers.</td>
 296   </tr>
 297   <tr>
 298     <td width="22%"><tt>support_dynamic_properties</tt></td>
 299     <td width="18%"><tt>CORBA::Boolean</tt></td>
 300     <td width="60%">Search considers offers with dynamic properties.</td>
 301   </tr>
 302   <tr>
 303     <td width="22%"><tt>support_modifiable_properties</tt></td>
 304     <td width="18%"><tt>CORBA::Boolean</tt></td>
 305     <td width="60%">Search considers offers with not readonly properties.</td>
 306   </tr>
 307   <tr>
 308     <td width="22%"><tt>starting_trader</tt></td>
 309     <td width="18%"><tt>CosTrading::TraderName</tt></td>
 310     <td width="60%">Query is forwarded across all links in the policy, and search begins at
 311     the final trader.</td>
 312   </tr>
 313   <tr>
 314     <td width="22%"><tt>hop_count</tt></td>
 315     <td width="18%"><tt>CORBA::ULong</tt></td>
 316     <td width="60%">Maximum depth a query should be propagated in the trader federation.</td>
 317   </tr>
 318   <tr>
 319     <td width="22%"><tt>link_follow_rule</tt></td>
 320     <td width="18%"><tt>CosTrading::FollowOption</tt></td>
 321     <td width="60%">Query propagates to other traders if the <tt>link_follow_rule</tt> permits
 322     it.</td>
 323   </tr>
 324 </table>
 325
 326 <p>The TAO Trading Service comes with a handy utility --- <tt>TAO_Policy_Manager</tt> ---
 327 for creating a policy sequence to pass to the query method that won't incur any
 328 exceptions. &nbsp; Use the <tt>TAO_Policy_Manager</tt> in the following way:</p>
 329
 330 <table border="1" width="100%" cellpadding="3">
 331   <tr>
 332     <td width="100%"><pre>TAO_Policy_Manager policies;
 333 policies.exact_type_match (CORBA::B_FALSE);
 334 policies.search_card (16*NUM_OFFERS);
 335 policies.match_card (16*NUM_OFFERS);
 336 policies.return_card (16*NUM_OFFERS);
 337 policies.link_follow_rule (CosTrading::local_only);
 338 const CosTrading::PolicySeq&amp; policy_seq = policies.policy_seq ();</pre>
 339     </td>
 340   </tr>
 341 </table>
 342
 343 <h3><a name="FilteringProperties">Filtering Properties</a></h3>
 344
 345 <p>If the client wants only a subset of the properties defined for a service type returned
 346 in matching offers, it can specify those property names in the <tt>desired_properties</tt>
 347 parameter of the query method. Pass the <tt>prop_names</tt> method of <tt>CosTrading::Lookup::SpecifiedProperties</tt>
 348 a <tt>CosTrading::PropNameSeq</tt>:</p>
 349
 350 <table border="1" width="100%" cellpadding="3">
 351   <tr>
 352     <td width="100%"><pre>char* props[] = {&quot;Name&quot;, &quot;Description&quot;, &quot;Location&quot;, &quot;Host_Name&quot; };
 353 CosTrading::Lookup::SpecifiedProps desired_props;
 354 CosTrading::PropertyNameSeq prop_name_seq (4, 4, props, CORBA::B_FALSE);
 355 desired_props.prop_names (prop_name_seq);</pre>
 356     </td>
 357   </tr>
 358 </table>
 359
 360 <h3><a name="OfferIterators">Offer Iterators</a></h3>
 361
 362 <p>Those offers returned from the query in excess of <tt>how_many</tt> are placed in an
 363 offer iterator for deferred retrieval. The <tt>CosTrading::OfferIterator::next_n</tt>
 364 method will allocate a sequence and fill it with either n offers, or if it has fewer than <tt>n</tt>
 365 offers, the remaining offers. The <tt>next_n</tt> method returns true if the iterator
 366 contains more offers, and false if it's been depleted. After finishing with the iterator,
 367 invoke its <tt>destroy</tt> method to release any server-side resources.</p>
 368
 369 <p>The following code is an example of obtaining offers from a <tt>CosTrading::OfferIterator</tt>:</p>
 370
 371 <table border="1" width="100%" cellpadding="3">
 372   <tr>
 373     <td width="100%"><pre>CORBA::Boolean any_left = CORBA::B_FALSE;
 374 CORBA::Environment _env;</pre>
 375     <pre>do
 376   {
 377     CosTrading::OfferSeq_ptr iter_offers_ptr;
 378     CosTrading::OfferSeq_out iter_offers_out (iter_offers_ptr);
 379
 380     any_left = offer_iterator-&gt;next_n (length,
 381                                        iter_offers_out,
 382                                        _env);
 383     ACE_CHECK_ENV_RETURN (_env, 0);
 384
 385     CosTrading::OfferSeq_var iter_offers (iter_offers_ptr);
 386     // Process offers...
 387
 388   } while (any_left);</pre>
 389     </td>
 390   </tr>
 391 </table>
 392
 393 <h3><a name="PropertyEvaluation">Property Evaluation</a></h3>
 394
 395 <p>After the client completes a query that used dynamic properties, to review the property
 396 values of the returned offers, it has to distinguish between <tt>Anys</tt> containing
 397 static properties and <tt>Anys</tt> containing dynamic property structures. The <tt>TAO_Property_Evaluator</tt>
 398 class is a handy utility to obtain property values that hides how it evalutes properties
 399 for the client --- by simple <tt>Any</tt> value extraction for static properties, or by
 400 calling back to a dynamic property interface. The <tt>TAO_Property_Evaluator</tt> caches
 401 the value of a dynamic property, and frees the allocated <tt>Anys</tt> during its
 402 destruction. </p>
 403
 404 <p>The following code demonstrates how to use the <tt>TAO_Property_Evaluator</tt> to dump
 405 the properties of an offer to the screen. </p>
 406
 407 <table border="1" width="100%" cellpadding="3">
 408   <tr>
 409     <td width="100%"><pre>TAO_Property_Evaluator prop_eval (prop_seq);
 410 for (int length = prop_seq.length (), k = 0; k &lt; length; k++)
 411   {
 412     ACE_DEBUG ((LM_DEBUG, &quot;%-15s: &quot;, prop_seq[k].name.in ()));
 413     ACE_TRY
 414       {
 415         CORBA::Boolean is_dynamic = prop_eval.is_dynamic_property (k);
 416         ACE_CHECK_ENV;
 417
 418         value = prop_eval.property_value(k, env);
 419         ACE_CHECK_ENV;
 420
 421         if (value != 0)
 422           CORBA::Any::dump (*value);
 423       }
 424     ACE_CATCHANY
 425       {
 426         ACE_DEBUG ((LM_DEBUG, &quot;Error retrieving property value.\n&quot;));
 427       }
 428     ACE_ENDTRY;
 429   }</pre>
 430     </td>
 431   </tr>
 432 </table>
 433
 434 <h2><a name="TheExporterRole">The Exporter Role --- Registering a Service Type and Offer</a></h2>
 435
 436 <p>Before an exporting client can register a new service offer with the Trading Service,
 437 it needs to ensure first that its service type is present in the service type repository
 438 of the target trader. The most efficient way to do this is to first invoke the <tt>export</tt>
 439 method on the <tt>Register</tt> interface, and if it raises an <tt>UnknownServiceType</tt>
 440 exception, obtain a reference to the Repository, add the Service Type, and attempt the <tt>export</tt>
 441 a second time. Here's the boilerplate code:</p>
 442
 443 <table border="1" width="100%" cellpadding="3">
 444   <tr>
 445     <td width="100%"><pre>CORBA::Object_var trading_obj =
 446   orb_ptr-&gt;resolve_initial_references (&quot;TradingService&quot;);
 447 CosTrading::Lookup_var lookup_if =
 448   CosTrading::Lookup::_narrow (trading_obj.in ());
 449 CosTrading::Register_var register_if = lookup_if-&gt;register_if ();
 450 CosTrading::TypeRepository_ptr obj = this-&gt;trader_-&gt;type_repos ();
 451 CosTradingRepos::ServiceTypeRepository_var str =
 452   CosTradingRepos::ServiceTypeRepository::_narrow (obj);
 453
 454 try
 455   {
 456     // Attempt to export the offer.
 457     offer_id = register_id-&gt;export (object_ref, type, props);
 458   }
 459 catch (const CosTrading::UnknownServiceType&, excp)
 460   {
 461     // If the ServiceTypeName wasn't found, we'll have to add the
 462     // type to the Service Type repository ourselves.
 463     str-&gt;add_type (type,
 464                    object_ref-&gt;_interface_repository_id (),
 465                    prop_struct_seq,
 466                    super_type_name_seq);
 467
 468     // Now we'll try again to register the offer.
 469     offer_id = reg-&gt;export (object_ref, type, this-&gt;tprops_);
 470   }
 471 catch (...)
 472   {
 473     // Sigh, all our efforts were for naught.
 474     throw ();
 475   }
 476     </td>
 477   </tr>
 478 </table>
 479
 480 <h3><a name="TheServiceTypeRepository">The Service Type Repository</a></h3>
 481
 482 <p>Creating a service type description is simply a matter of filling in two sequences: a <tt>CosTradingRepos::ServiceTypeRepository::PropStructSeq</tt>
 483 and a <tt>CosTradingRepos::ServiceTypeRepository::ServiceTypeNameSeq</tt>. When filling in
 484 the <tt>value_type</tt> field, remember to up the reference count of the <tt>TypeCode</tt>,
 485 since otherwise the <tt>TypeCode_var</tt> will sieze control of the memory and free it.
 486 Here's a code excerpt taken from <tt>export_test</tt> showing how to build the first
 487 couple elements of such sequences:</p>
 488
 489 <table border="1" width="100%" cellpadding="3">
 490   <tr>
 491     <td width="100%"><pre>this-&gt;type_structs_[TT_Info::PLOTTER].props.length (2);
 492 this-&gt;type_structs_[TT_Info::PLOTTER].super_types.length (1);
 493 this-&gt;type_structs_[TT_Info::PLOTTER].super_types[0] =
 494 TT_Info::INTERFACE_NAMES[TT_Info::REMOTE_IO];
 495 this-&gt;type_structs_[TT_Info::PLOTTER].props[0].name =
 496 TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_NUM_COLORS];
 497 this-&gt;type_structs_[TT_Info::PLOTTER].props[0].value_type =
 498 CORBA::TypeCode::_duplicate (CORBA::_tc_long);
 499 this-&gt;type_structs_[TT_Info::PLOTTER].props[0].mode =
 500 CosTradingRepos::ServiceTypeRepository::PROP_NORMAL;
 501 this-&gt;type_structs_[TT_Info::PLOTTER].props[1].name =
 502 TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_AUTO_LOADING];
 503 this-&gt;type_structs_[TT_Info::PLOTTER].props[1].value_type =
 504 CORBA::TypeCode::_duplicate (CORBA::_tc_boolean);
 505 this-&gt;type_structs_[TT_Info::PLOTTER].props[1].mode =
 506 CosTradingRepos::ServiceTypeRepository::PROP_READONLY;</pre>
 507     </td>
 508   </tr>
 509 </table>
 510
 511 <h3><a name="ExportingWithdrawingandModifying">Exporting, Withdrawing, and Modifying
 512 Service Offers</a></h3>
 513
 514 <p>Like with adding a Service Type, exporting an offer is just filling in the sequences.
 515 For offers, of course, property values are passed, so this involves employing the <tt>Any</tt>
 516 insertion operators. Here's a code exerpt from <tt>export_test</tt>:</p>
 517
 518 <table border="1" width="100%" cellpadding="3">
 519   <tr>
 520     <td width="100%"><pre>CosTrading::PropertySeq prop_seq (2);
 521 prop_seq[0].name =
 522   TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_NUM_COLORS];
 523 prop_seq[0].value &lt;&lt;= ACE_static_cast (CORBA::Long, 256);
 524 prop_seq[1].name =
 525   TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_AUTO_LOADING];
 526 prop_seq[1].value &lt;&lt;= CORBA::Any::from_boolean (CORBA::B_TRUE);</pre>
 527     </td>
 528   </tr>
 529 </table>
 530
 531 <p>The <tt>export_test</tt> returns a <tt>CosTrading::OfferId</tt> string, which is
 532 required to perform the <tt>withdraw</tt> and <tt>modify</tt> operations on the exported
 533 offer. <tt>withdraw</tt> requires that you simply pass the <tt>OfferId</tt> of the offer
 534 to be withdrawn, while <tt>modify</tt> takes two additional sequences: a <tt>CosTrading::PropertyNameSeq</tt>
 535 of property names to be removed from the offer, and a <tt>CosTrading::PropertySeq</tt> of
 536 offers to be added or changed in the offer. </p>
 537
 538 <h3><a name="ImplementingDynamicProperties">Implementing Dynamic Properties</a></h3>
 539
 540 <p>To export an offer with a dynamic property:
 541
 542 <ul>
 543   <li>inherit from the <tt>TAO_Dynamic_Property</tt> class and implement its <tt>DP_Eval</tt>
 544     method; </li>
 545   <li>create a <tt>CosTradingDynamic::DynamicProperty</tt> structure using the <tt>TAO_Dynamic_Property::construct_dynamic_prop</tt>
 546     method; </li>
 547   <li>insert the <tt>CosTradingDynamic::DynamicProperty</tt> in the value field of the
 548     property. </li>
 549 </ul>
 550
 551 <p>The following code, taken from the <tt>export_test</tt> example, illustrates this:</p>
 552
 553 <table border="1" width="100%" cellpadding="3">
 554   <tr>
 555     <td width="100%"><pre>// Step 1: Write the Dynamic Property callback handler.
 556 class Simple_DP : public TAO_Dynamic_Property
 557 {
 558 public:
 559
 560   virtual CORBA::Any* evalDP (const char* name,
 561                               CORBA::TypeCode_ptr returned_type,
 562                               const CORBA::Any&amp; extra_info,
 563                               CORBA::Environment&amp; _env)
 564     ACE_THROW_SPEC ((CosTradingDynamic::DPEvalFailure));
 565 };
 566
 567 CORBA::Any*
 568 Simple_DP::evalDP (const char* name,
 569                    CORBA::TypeCode_ptr returned_type,
 570                    const CORBA::Any&amp; extra_info,
 571                    CORBA::Environment&amp; _env)
 572   ACE_THROW_SPEC ((CosTradingDynamic::DPEvalFailure))
 573 {
 574   CORBA::Any* return_value = 0;
 575   ACE_NEW_RETURN (return_value, CORBA::Any, 0);
 576
 577   (*return_value) &lt;&lt;= ACE_static_cast (CORBA::ULong, ACE_OS::rand ());
 578   return return_value;
 579 }</pre>
 580     <pre>// Step 2: Create the Dynamic Property
 581 Simple_DP dp;
 582 CORBA::Any extra_info;
 583 CosTrading::PropertySeq prop_seq (1);
 584 CosTrading::DynamicProp* dp_struct =
 585   dp.construct_dynamic_prop (&quot;prop_name&quot;,
 586                              CORBA::_tc_ulong,
 587                              extra_info);</pre>
 588     <pre>// Step 3: Turn over the dynamic property to the propery value Any.
 589 CORBA::Environment env;
 590 prop_seq[0].name = &quot;prop_name&quot;;
 591 prop_seq[0].value.replace (CosTrading::_tc_DynamicProp,
 592                            dp_struct,
 593                            CORBA::B_TRUE,
 594                            env);
 595 ACE_CHECK_ENV_RETURN (env, -1);</pre>
 596     </td>
 597   </tr>
 598 </table>
 599
 600 <h2><a name="TheAdministratorRole">The Administrator Role --- Tweaking Policies and
 601 Adjusting Links</a></h2>
 602
 603 <p>The trader can be configured remotely through two interfaces: the <tt>Admin</tt>
 604 interface, for tweaking global policies, enabling and disabling interfaces, and dumping
 605 the trader contents; and the <tt>Link</tt> interface, for attaching to and detaching from
 606 other traders. </p>
 607
 608 <p>Adjusting policies is straightforward. Here's an example of setting the <tt>max_search_card</tt>
 609 policy:</p>
 610
 611 <table border="1" width="100%" cellpadding="3">
 612   <tr>
 613     <td width="100%"><pre>// lookup_if returned from resolve_initial_references.
 614 CosTrading::Admin_var admin_if =
 615   lookup_if-&gt;admin_if ();
 616 </pre>
 617     <pre>admin_if-&gt;set_max_match_card (200);</pre>
 618     </td>
 619   </tr>
 620 </table>
 621
 622 <p>Here's an example of using the list_offers method on the Admin interface to remove all
 623 offers from the Trader:</p>
 624
 625 <table border="1" width="100%" cellpadding="3">
 626   <tr>
 627     <td width="100%"><pre>
 628 {
 629 CosTrading::OfferIdIterator_ptr offer_id_iter;
 630 CosTrading::OfferIdSeq_ptr offer_id_seq;
 631
 632 // lookup_if returned from resolve_initial_references.
 633 CosTrading::Admin_var admin_if =
 634   lookup_if-&gt;admin_if ();
 635
 636 CosTrading::Register_var register_if =
 637   lookup_if-&gt;register_if ();
 638
 639 admin_if-&gt;list_offers (10,
 640                        CosTrading::OfferIdSeq_out (offer_id_seq),
 641                        CosTrading::OfferIdIterator_out (offer_id_iter));
 642
 643 if (offer_id_seq != 0)
 644  {
 645    CosTrading::OfferIdSeq_var offer_id_seq_var (offer_id_seq);
 646    for (CORBA::ULong i = 0; i &lt; offer_id_seq_var.length (); i++)
 647      {
 648        register_if-&gt;withdraw (offer_id_seq_var[i]);
 649      }
 650  }
 651
 652 if (offer_id_iter != CosTrading::OfferIdIterator::_nil ())
 653  {
 654    CORBA::Boolean any_left = CORBA::B_FALSE;
 655    CosTrading::OfferIdSeq_ptr id_seq = 0;
 656    CosTrading::OfferIdIterator_var offer_id_iter_var (offer_id_iter);
 657
 658    do
 659      {
 660        any_left =
 661          offer_id_iter-&gt;next_n (length,
 662                                 CosTrading::OfferIdSeq_out (id_seq));
 663
 664        CORBA::ULong offers = id_seq-&gt;length ();
 665        for (CORBA::ULong i = 0; i &lt; offers; i++)
 666         {
 667           register_if-&gt;withdraw (id_seq[i]);
 668         }
 669
 670        delete id_seq;
 671      }
 672    while (any_left);
 673
 674    offer_id_iter-&gt;destroy ();
 675  }
 676 }
 677 catch (...)
 678 {
 679   // Handle Errors.
 680 }
 681 </pre>
 682     </td>
 683   </tr>
 684 </table>
 685
 686 <p>Here's an example a trader linking itself to another trader (<tt>this-&gt;trader_</tt>
 687 is a colocated trader --- see the next section for more information): </p>
 688
 689 <table border="1" width="100%" cellpadding="3">
 690   <tr>
 691     <td width="100%"><pre>
 692  {
 693    CosTrading::Link_var link_if =  lookup_if-&gt;link_if ();
 694
 695    TAO_Trading_Components_Impl&amp; trd_comp =
 696      this-&gt;trader_-&gt;trading_components ();
 697    CosTrading::Lookup_ptr our_lookup = trd_comp.lookup_if ();
 698    CosTrading::Link_ptr our_link = trd_comp.link_if ();
 699
 700    link_if-&gt;add_link (this-&gt;name_.in (),
 701                       our_lookup,
 702                       CosTrading::always,
 703                       CosTrading::always);
 704
 705    our_link-&gt;add_link (&quot;Bootstrap_Trader&quot;,
 706                        lookup_if.in (),
 707                        CosTrading::always,
 708                        CosTrading::always);
 709  }
 710 catch (...)
 711 {
 712   // Handle Errors.
 713 }
 714 </pre>
 715     </td>
 716   </tr>
 717 </table>
 718
 719 <hr>
 720
 721 <h1><a name="TheServerRole">The Server Role</a></h1>
 722
 723 <p>The TAO Trading Service comes with an out-of-the-box executable suitable for common
 724 use. However, it can also easily be colocated with any other TAO server to add Trading
 725 Service functionality to that server.</p>
 726
 727 <h2><a name="TheTAOTradingServiceApplication">The TAO Trading Service Application</a></h2>
 728
 729 <p>This out-of-the-box server takes a number of command line arguments:</p>
 730
 731 <table border="1" width="100%" cellpadding="3">
 732   <tr>
 733     <td width="26%"><tt>-TSthreadsafe</tt></td>
 734     <td width="74%">The Trader will use reader/writer locks to protect the offer database and
 735     link collection, and normal thread mutexes for the rest of the shared state --- global
 736     policies, support attributes, and interface accessors. (default is not thread safe; Null
 737     Mutexes are used)</td>
 738   </tr>
 739   <tr>
 740     <td width="26%"><tt>-TSconformance</tt></td>
 741     <td width="74%">Determines which conformance category the Trading Service will meet:<br>
 742     <table border="0" width="100%" cellpadding="3">
 743       <tr>
 744         <td width="18%"><ul>
 745           <li><em>query</em></li>
 746         </ul>
 747         </td>
 748         <td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt> interface only</td>
 749       </tr>
 750       <tr>
 751         <td width="18%"><ul>
 752           <li><em>simple</em></li>
 753         </ul>
 754         </td>
 755         <td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt> and <tt>Register</tt>
 756         interfaces</td>
 757       </tr>
 758       <tr>
 759         <td width="18%"><ul>
 760           <li><em>standalone</em></li>
 761         </ul>
 762         </td>
 763         <td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt>, <tt>Register</tt>,
 764         and <tt>Admin</tt> interfaces</td>
 765       </tr>
 766       <tr>
 767         <td width="18%"><ul>
 768           <li><em>linked</em></li>
 769         </ul>
 770         </td>
 771         <td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt>, <tt>Register</tt>,
 772         <tt>Admin</tt>, and <tt>Link</tt> interfaces (default)</td>
 773       </tr>
 774     </table>
 775     </td>
 776   </tr>
 777   <tr>
 778     <td width="26%"><tt>-TSsupports_dynamic_properties</tt></td>
 779     <td width="74%"><table border="0" width="100%" cellpadding="3">
 780       <tr>
 781         <td width="18%"><ul>
 782           <li><em>true</em></li>
 783         </ul>
 784         </td>
 785         <td width="82%" valign="top" align="left">Will consider offers with dynamic properties in
 786         queries unless explicitly disabled by a policy passed to the query method. (default)</td>
 787       </tr>
 788       <tr>
 789         <td width="18%"><ul>
 790           <li><em>false</em></li>
 791         </ul>
 792         </td>
 793         <td width="82%" valign="top" align="left">Will not consider offers with dynamic properties
 794         in queries, unless explicitly enabled by a policy passed to the query method.</td>
 795       </tr>
 796     </table>
 797     </td>
 798   </tr>
 799   <tr>
 800     <td width="26%"><tt>-TSsupports_modifiable_properties</tt></td>
 801     <td width="74%"><table border="0" width="100%" cellpadding="3">
 802       <tr>
 803         <td width="18%"><ul>
 804           <li><em>true</em></li>
 805         </ul>
 806         </td>
 807         <td width="82%" valign="top" align="left">Will consider offers with not explicitly
 808         modifable properties in queries unless explicitly disabled by a policy passed to the query
 809         method. Enables the <tt>modify</tt> method on the <tt>Register</tt> interface. (default)</td>
 810       </tr>
 811       <tr>
 812         <td width="18%"><ul>
 813           <li><em>false</em></li>
 814         </ul>
 815         </td>
 816         <td width="82%" valign="top" align="left">Will not consider dynamic properties in queries,
 817         unless explicitly overridden by a query policy. Diables <tt>modify</tt> method on the <tt>Register</tt>
 818         interface.</td>
 819       </tr>
 820     </table>
 821     </td>
 822   </tr>
 823   <tr>
 824     <td width="26%"><tt>-TSdef_search_card</tt></td>
 825     <td width="74%">Search cardinality if none is specified as a query policy. (default is
 826     200)</td>
 827   </tr>
 828   <tr>
 829     <td width="26%"><tt>-TSmax_search_card</tt></td>
 830     <td width="74%">Upper limit on the search cardinality for a query. (default is 500)</td>
 831   </tr>
 832   <tr>
 833     <td width="26%"><tt>-TSdef_match_card</tt></td>
 834     <td width="74%">Match cardinality if none is specified as a query policy. (default is 200)</td>
 835   </tr>
 836   <tr>
 837     <td width="26%"><tt>-TSmax_match_card</tt></td>
 838     <td width="74%">Upper limit on the match cardinality for a query. (default is 500)</td>
 839   </tr>
 840   <tr>
 841     <td width="26%"><tt>-TSdef_return_card</tt></td>
 842     <td width="74%">Return cardinality if none is specified as a query policy. (default is
 843     200)</td>
 844   </tr>
 845   <tr>
 846     <td width="26%"><tt>-TSmax_return_card</tt></td>
 847     <td width="74%">Upper limit on the return cardinality for a query. (default is 500)</td>
 848   </tr>
 849   <tr>
 850     <td width="26%"><tt>-TSdef_hop_count</tt></td>
 851     <td width="74%">The depths a federated query may go if no query policy is specified.
 852     (default 5)</td>
 853   </tr>
 854   <tr>
 855     <td width="26%"><tt>-TSmax_hop_count</tt></td>
 856     <td width="74%">The maximum number of links a federated query can travel after it passes
 857     through this trader. (default is 10) </td>
 858   </tr>
 859   <tr>
 860     <td width="26%"><tt>-TSdef_follow_policy</tt></td>
 861     <td width="74%"><table border="0" width="100%" cellpadding="3">
 862       <tr>
 863         <td width="18%"><ul>
 864           <li><em>always</em></li>
 865         </ul>
 866         </td>
 867         <td width="82%" valign="top" align="left">The trader will always pass a query onto the
 868         next available linked trader.</td>
 869       </tr>
 870       <tr>
 871         <td width="18%"><ul>
 872           <li><em>if_no_local</em></li>
 873         </ul>
 874         </td>
 875         <td width="82%" valign="top" align="left">The trader will pass a query onto the next
 876         trader only if the local search produced no results. (default)</td>
 877       </tr>
 878       <tr>
 879         <td width="18%"><ul>
 880           <li><em>local_only</em></li>
 881         </ul>
 882         </td>
 883         <td width="82%" valign="top" align="left">The trader will never pass on a query.</td>
 884       </tr>
 885     </table>
 886     </td>
 887   </tr>
 888   <tr>
 889     <td width="26%"><tt>-TSmax_follow_policy</tt></td>
 890     <td width="74%"><table border="0" width="100%" cellpadding="3">
 891       <tr>
 892         <td width="18%"><ul>
 893           <li><em>always</em></li>
 894         </ul>
 895         </td>
 896         <td width="82%" valign="top" align="left">The trader doesn't limit the importer to the
 897         local offer space. (default)</td>
 898       </tr>
 899       <tr>
 900         <td width="18%"><ul>
 901           <li><em>if_no_local</em></li>
 902         </ul>
 903         </td>
 904         <td width="82%" valign="top" align="left">The trader refuses to pass on queries of the
 905         local search matched offers.</td>
 906       </tr>
 907       <tr>
 908         <td width="18%"><ul>
 909           <li><em>local_only</em></li>
 910         </ul>
 911         </td>
 912         <td width="82%" valign="top" align="left">The trader will never allow federated queries.</td>
 913       </tr>
 914     </table>
 915     </td>
 916   </tr>
 917   <tr>
 918     <td width="26%"><tt>-ORBtradingserviceport</tt></td>
 919     <td width="74%">Port on which to listen for multicast bootstrap requests.</td>
 920   </tr>
 921   <tr>
 922     <td width="26%"><tt>-ORBtradingserviceport</tt></td>
 923     <td width="74%">Port on which to listen for multicast bootstrap requests.</td>
 924   </tr>
 925   <tr>
 926     <td width="26%"><tt>-TSdumpior</tt></td>
 927     <td width="74%">Dumps the trader's IOR to a file (default is stdout).</td>
 928   </tr>
 929 </table>
 930
 931 <p>By default the trader will listen for multicast <tt>resolve_initial_references</tt>
 932 requests, and respond with the IOR of its <tt>Lookup</tt> inteface. For the purposes of
 933 testing federated queries, when passed the <tt>-TSfederate</tt> method, instead of
 934 becoming a bootstrappable server, the <tt>Trading_Service</tt> application will bootstrap
 935 itself to a multicast trader, link itself to that trader and every other trader accessible
 936 through that trader. This protocol will have all traders on the multicast network form a
 937 complete graph. </p>
 938
 939 <h2><a name="ColocatingtheTradingServiceinaTAOApplication">Colocating the Trading Service
 940 in a TAO Application</a></h2>
 941
 942 <p>Colocating the Trading Service in a TAO application amounts to constructing a <tt>TAO_TRADER</tt>
 943 object using the <tt>TAO_Trader_Factory::construct_trader</tt> call. The <tt>argc</tt> and
 944 <tt>argv</tt> parameters to <tt>construct_trader</tt> contain the configuration parameters
 945 described in the previous section. The trader is also configurable programatically through
 946 its attribute classes. The follow code exerpt demonstrates this. </p>
 947
 948 <p>In addition the application will need to create a service type repository
 949 implementation --- TAO's being the <tt>TAO_Service_Type_Repository</tt> --- and configure
 950 the trader with it. The service type repository is separate from the trader in this way to
 951 allow, for example, multiple traders to share the same service type repository. The
 952 following code exerpt also demontrates configuring the repository:</p>
 953
 954 <table border="1" width="100%" cellpadding="3">
 955   <tr>
 956     <td width="100%"><pre>TAO_TRADER* trader = TAO_Trader_Factory::create_trader (argc, argv);
 957 TAO_Support_Attributes_Impl&amp; sup_attr = trader-&gt;support_attributes ();
 958 TAO_Import_Attributes_Impl&amp; imp_attr = trader-&gt;trading_components ();
 959
 960 // Configure the trader with a service type repository.
 961 CORBA::Environment _env;
 962 TAO_Service_Type_Repository type_repos* type_repos = 0;
 963 ACE_NEW (type_repos, TAO_Service_Type_Repository);
 964 sup_attr.type_repos (type_repos-&gt;_this (_env));
 965 ACE_CHECK_ENV_RETURN (_env, -1);</pre>
 966     <pre>// Configure other policies, overriding the command line arguments.
 967 imp_attr.search_card (20);
 968 sup_attr.supports_dynamic_properties (CORBA::B_FALSE);</pre>
 969     </td>
 970   </tr>
 971 </table>
 972
 973 <p>The trader interfaces register themselves with the default POA during the Trading
 974 Service's construction. All that remains is to activate the POA and enter the ORB event
 975 loop. </p>
 976
 977 <hr>
 978
 979 <h1><a name="RunningtheTradingServiceTests">Running the Trading Service Tests</a></h1>
 980
 981 <p>There are two executables that test the Trading Service functionality --- one to test
 982 the exporter role, and the other, the importer role. To run the tests simply launch the <tt>Trading_Service</tt>
 983 application, then run the <tt>export_test</tt> executable found in the <tt>orbsvcs/tests/Trading</tt>
 984 directory. When the <tt>export_test</tt> ceases to output data and enters the event loop,
 985 run the <tt>import_test</tt> found in the same directory. </p>
 986
 987 <p>Also of importance: the <tt>-TSdumpior filename </tt> argument to the trader dumps
 988 its IOR to the file. You can then paste the contents on the command line to
 989 the tests with <tt>-ORBtradingserviceior IOR</tt>, or into the environment variable
 990 <tt>TradingServiceIOR</tt>.</p>
 991
 992 <p>The expected output of the tests can be found in the README file in the
 993 tests directory.</p>
 994
 995 <p>To test federated queries, run at least three copies of the <tt>Trading_Service</tt>
 996 application, each using the <tt>-TSfederate</tt> flag. The traders will form a complete
 997 graph, with each link follow policy set to <tt>CosTrading::always</tt>. When run with the <tt>-f</tt>
 998 flag, the <tt>export_test</tt> will add the service types and export offers to each of the
 999 traders in the federation. When run with the <tt>-f</tt> flag, the <tt>import_test </tt>will
1000 perform a directed query to a trader two links distant from the trader boostrapped to, in
1001 addition to performing federated queries.&nbsp;&nbsp; </p>
1002
1003 <p>By default the tests dump the contents of service types and offers to the screen so the
1004 tester can validate the results. To run the tests in quiet mode, where the results of the
1005 describe and query methods are concealed, use the <tt>-q</tt> flag.</p>
1006
1007 <hr>
1008
1009 <h1><a name="KnownBugsandWorkarounds">Known Bugs and Workarounds</a></h1>
1010
1011     <p>At this point there are no known problems with TAO that affect the
1012       Trading service.</p>
1013
1014 <hr>
1015
1016 <h1><a name="FutureWork">Future Work</a></h1>
1017
1018 <ul>
1019   <li><strong>Persistence</strong> --- Have the Trading Service offer database and service
1020     type repository survive the lifetime of a single Trading Service process. This would be
1021     accomplished by either taking advantage of the ability to serialize IDL types --- using
1022     CDR streams --- or through memory-mapped files, <em>a la </em>the ACE Naming Service.</li>
1023 </ul>
1024
1025 <ul>
1026   <li><strong>The <tt>Proxy</tt> Interface </strong>--- Should we ever feel so motivated, we
1027     might implement the <tt>Proxy</tt> interface.&nbsp; </li>
1028 </ul>
1029
1030 <hr>
1031
1032 <address>
1033   <a href="mailto:sbw1@cs.wustl.edu">Seth Benjamin Widoff</a>
1034 </address>
1035 <!-- Created: Mon Jun 29 12:26:36 CDT 1998 -->
1036 <!-- hhmts start -->
1037 </body>
1038 </html>