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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
<head>
<title>TAO Trading Service Documentation</title>
</head>
<body text="#000000" link="#0000FF" vlink="#CC0000" bgcolor="#FFFFFF">
<hr>
<h1 align="center">TAO Trading Service Documentation</h1>
<hr>
<p>The TAO transient Trading Service implements the COS TradingObject Service
specification, and conforms to the Linked Trader conformance criteria. This document
details how to use the TAO Trading Service from the following perspectives:
<ul>
<li>as an importer bootstrapping to the Trading Service;</li>
<li>as a service offer exporter;</li>
<li>as an administrator;</li>
<li>as an out-of-the-box server process; </li>
<li>as a collocated object. </li>
</ul>
<p>In addition, it covers running the Trading Service tests and discusses known bugs and
workarounds.</p>
<p>This document assumes you are familiar with Trading Service concepts, such as
"importer," "exporter", "service type", "service
offer," and "dynamic property", as well as the roles of each of the Trading
Service's interfaces --- <tt>Lookup</tt>, <tt>Register</tt>, <tt>Admin</tt>, and <tt>Link</tt>
(the TAO implementation doesn't currently support <tt>Proxy</tt>). I recommend reading the
first two sections of the <a href="ftp://www.omg.org/pub/docs/formal/97-12-23.pdf">Trading
Service specification</a>. This document has the following layout:
<ol>
<li><a href="#TheClientRole">The Client Role</a> <ul>
<li><a href="#BootstrappingtotheTradingService">Bootstrapping to the Trading Service</a> </li>
<li><a href="#The ImporterRolePerformingaQuery">The Importer Role --- Performing a Query</a><ul>
<li><a href="#Constraints">Constraints</a></li>
<li><a href="#Preferences">Preferences</a></li>
<li><a href="#Policies">Policies</a></li>
<li><a href="#FilteringProperties">Filtering Properties</a> </li>
<li><a href="#OfferIterators">Offer Iterators</a></li>
<li><a href="#PropertyEvaluation">Property Evaluation</a></li>
</ul>
</li>
<li><a href="#TheExporterRole">The Exporter Role --- Registering a Service Type and Offer</a>
<ul>
<li><a href="#TheServiceTypeRepository">The Service Type Repository</a> </li>
<li><a href="#ExportingWithdrawingandModifying">Exporting, Withdrawing, and Modifying
Service Offers</a> </li>
<li><a href="#ImplementingDynamicProperties">Implementing Dynamic Properties</a></li>
</ul>
</li>
<li><a href="#TheAdministratorRole">The Administrator Role --- Tweaking Policies and
Adjusting Links</a></li>
</ul>
</li>
<li><a href="#TheServerRole">The Server Role</a><ul>
<li><a href="#TheTAOTradingServiceApplication">The TAO <tt>Trading_Service</tt> Application</a></li>
<li><a href="#ColocatingtheTradingServiceinaTAOApplication">Colocating the Trading Service
in a TAO Application</a></li>
</ul>
</li>
<li><a href="#RunningtheTradingServiceTests">Running the Trading Service Tests</a></li>
<li><a href="#KnownBugsandWorkarounds">Known Bugs and Workarounds</a></li>
<li><a href="#FutureWork">Future Work</a></li>
</ol>
<hr>
<h1><a name="TheClientRole">The Client Role</a></h1>
<p align="left">There are three categories of operations that a client can perform on a
Trading Service instance: exporting a service offer to the Trading Service, importing a
list of Service Offers whose properties satisfy a constraint expression, and attending to
administrative duties --- tweaking policies or adjusting links. The first order of
business, of course, is obtaining a reference to a Trading Service instance, assuming that
instance is not colocated with the client. </p>
<h2 align="left"><a name="BootstrappingtotheTradingService">Bootstrapping to the Trading
Service</a></h2>
<p align="left">Like with the Naming Service, the ORB will obtain a reference to a Trading
Service instance's <tt>Lookup</tt> interface when a client invokes the <tt>CORBA::ORB::resolve_initial_references</tt>
method and passes to it the <tt>ObjectID</tt> "<tt>TradingService</tt>". The
following TAO code bootstraps to the Trading Service:</p>
<table border="1" width="100%" cellpadding="6">
<tr>
<td width="100%"><pre>TAO_TRY
{
TAO_ORB_Manager orb_manager;
orb_manager.init (argc, argv, TAO_TRY_ENV);
TAO_CHECK_ENV;
CORBA::ORB_var orb = orb_manager.orb ();
CORBA::Object_var trading_obj =
orb->resolve_initial_references ("TradingService");
CosTrading::Lookup_var lookup_if =
CosTrading::Lookup::_narrow (trading_obj.in (), TAO_TRY_ENV);
TAO_CHECK_ENV;
}
TAO_CATCHANY
{
TAO_TRY_ENV.print_exception ("Failed to bootstrap to a trader");
}
TAO_ENDTRY;</pre>
</td>
</tr>
</table>
<p>The first time <tt>resolve_initial_references</tt> is called, the ORB uses a multicast
protocol to locate an existing trader. The ORB emits a multicast packet containing a field
identifying the desired service --- Naming or Trading --- and the port number that the
client is listening on for the response (the IP address can be inferred from the packet).
When the trader receives the packet and finds that the id contained within matches its
own, it opens a socket to the client on the designated port, and sends its IOR, which the
ORB converts to an object reference that it caches. </p>
<p>If the trader IOR is known ahead of time, the string can be passed to the client in the
environment variable <tt>TradingService</tt>, or by the command line option <tt>-ORBtradingserviceior
<IOR></tt>. Likewise, if the multicast port is known ahead of time and differs from
the default port, the port number can be passed to the client in the environment variable <tt>TradingServicePort</tt>,
or by the command line option <tt>-ORBtradingserviceport <PORTNUM></tt>. </p>
<h2><a name="The ImporterRolePerformingaQuery">The Importer Role --- Performing a Query</a></h2>
<p>Once the importer has obtained a reference to a trader's <tt>Lookup</tt> interface, it
next needs to fire up a query. The query method takes nine parameters (aside from the <tt>CORBA::Environment</tt>):</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="39%"><tt>const CosTrading::ServiceTypeName</tt></td>
<td width="61%">The Trading Service will search Offers belonging to this subtype. If the <tt>exact_type_match</tt>
policy wasn't explicitly set to false, then offers belonging to subtypes of this type will
also be searched. </td>
</tr>
<tr>
<td width="39%"><tt>const CosTrading::Constraint</tt></td>
<td width="61%">An expression in the OMG standard constraint language, where each property
name is a property defined in the Service Type description of the type being searched.</td>
</tr>
<tr>
<td width="39%"><tt>const CosTrading::Preference</tt></td>
<td width="61%">An expression in the OMG standard constraint language dictating how offers
in the <tt>returned_offers</tt> sequence should be ordered.</td>
</tr>
<tr>
<td width="39%"><tt>const CosTrading::PolicySeq</tt></td>
<td width="61%">Policies governing the breadth of search and the type of permissible
offers. A policy is a name/value pair --- a string and an <tt>Any</tt> --- that affect the
search algorithm. </td>
</tr>
<tr>
<td width="39%"><tt>const CosTrading::Lookup::SpecifiedProps</tt></td>
<td width="61%">A union specifying which properties should be returned in each offer. If
the descriminator is <tt>CosTrading::Lookup::some</tt>, the union contains the list
of designated property names. Other options are <tt>all</tt>or <tt>none</tt>. </td>
</tr>
<tr>
<td width="39%"><tt>CORBA::ULong how_many</tt></td>
<td width="61%">The number of offers that should be placed in the returned sequence.</td>
</tr>
<tr>
<td width="39%"><tt>CosTrading::OfferSeq_out</tt></td>
<td width="61%">A list of ordered offers whose properties meet the constraints.</td>
</tr>
<tr>
<td width="39%"><tt>CosTrading::OfferIterator_out</tt></td>
<td width="61%">Iterator over returned offers in excess of how_many --- unordered.</td>
</tr>
<tr>
<td width="39%"><tt>CosTrading::PolicyNameSeq_out</tt></td>
<td width="61%">A sequence of policy names for policies that limited the search.</td>
</tr>
</table>
<h3><a name="Constraints">Constraints</a></h3>
<p>A constraint is a string in the OMG standard constraint language (the BNF can be found
at the end of the specification). The trader iterates over applicable offers, and for each
offer determines if its properties meet the constraints, replacing property names in the
string with their values and computing the result. If the constraint evaluates to true,
the offer is placed in the pool of matched offers. If the constraint string is
syntactically invalid, contains property names not found in the service type description
for the listed service type, or has operators with mismatched operand types, the query
method will throw an <tt>InvalidConstraint</tt> exception. </p>
<p>Operands can be of two types: property names or literals. A property name is an
unquoted string of alphanumeric characters and underscores that begins with a letter. The
service type describes the type of a property. A literal is an signed or unsigned integer,
floating point number --- scientific notation acceptable ---, single-quoted string, or
boolean --- written TRUE or FALSE. </p>
<p>The constraint language supports the following operations:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="25%">Arithmetic (+, -, *, /)</td>
<td width="34%"><tt>Disk_Space*1000 - Amount_Used/10</tt></td>
<td width="41%">Accepts two numeric operands.</td>
</tr>
<tr>
<td width="25%">Inequality (<,>,<=,>=)</td>
<td width="34%"><tt>Amount_Used < Disk_Space</tt></td>
<td width="41%">Accepts two numeric or two string operands.</td>
</tr>
<tr>
<td width="25%">Equality (==, !=)</td>
<td width="34%"><tt>Amount_Used == Disk_Space</tt></td>
<td width="41%">Accepts two numeric, two string, or two boolean operands.</td>
</tr>
<tr>
<td width="25%">Substring (~)</td>
<td width="34%"><tt>'.wustl.edu' ~ Domain_Name</tt></td>
<td width="41%">Accept two string operands. Returns true if the right string contains the
left.</td>
</tr>
<tr>
<td width="25%">Sequence inclusion (in)</td>
<td width="34%"><tt>'sbw1' in User_Queue</tt></td>
<td width="41%">Accepts an operand of a primitive CORBA type on the left, and a sequence
of the same type on the right. Returns true when the sequence contains the value in the
left operand, false otherwise.</td>
</tr>
<tr>
<td width="25%">Property existence (exist)</td>
<td width="34%"><tt>exist User_Queue</tt></td>
<td width="41%">Accepts a property name. Returns true if the property is defined in the
offer.</td>
</tr>
</table>
<h3><a name="Preferences">Preferences</a></h3>
<p>A preference is a constraint language string that determines the order of offers in the
returned offer sequence. There are five types of preferences:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="18%"><tt>min</tt> <expression></td>
<td width="82%">Offers are ordered by ascending expression value. The expression must
return a number.</td>
</tr>
<tr>
<td width="18%"><tt>max</tt> <expression> </td>
<td width="82%">Offers are ordered by descending expression value. The expression must
return a number. </td>
</tr>
<tr>
<td width="18%"><tt>with</tt> <expression></td>
<td width="82%">Offers are partitioned into two parts: those offers for which the
expression returns true are placed in the front, the rest in the back. The expression must
return a boolean value.</td>
</tr>
<tr>
<td width="18%"><tt>random</tt></td>
<td width="82%">Offers in the sequence are shuffled.</td>
</tr>
<tr>
<td width="18%"><tt>first</tt></td>
<td width="82%">Offers are placed in the sequence in the order they're evaluated.</td>
</tr>
</table>
<h3><a name="Policies">Policies</a></h3>
<p>The following import policies are descibed in the specification and supported by the
TAO Trading Service:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="22%"><tt>exact_type_match</tt></td>
<td width="18%"><tt>CORBA::Boolean</tt></td>
<td width="60%">True --- Search only considers offers belonging to the given type.<br>
False --- Search considers offers belonging to the given type or any of its subtypes.</td>
</tr>
<tr>
<td width="22%"><tt>search_card</tt></td>
<td width="18%"><tt>CORBA::ULong</tt></td>
<td width="60%">Search ceases after <tt>search_card</tt> number of offers have been
evaluated.</td>
</tr>
<tr>
<td width="22%"><tt>match_card</tt></td>
<td width="18%"><tt>CORBA::ULong</tt></td>
<td width="60%">Search ceases after <tt>search_card</tt> number of offers have been
matched.</td>
</tr>
<tr>
<td width="22%"><tt>return_card</tt></td>
<td width="18%"><tt>CORBA::ULong</tt></td>
<td width="60%">Query returns at most <tt>return_card</tt> number of offers.</td>
</tr>
<tr>
<td width="22%"><tt>support_dynamic_properties</tt></td>
<td width="18%"><tt>CORBA::Boolean</tt></td>
<td width="60%">Search considers offers with dynamic properties.</td>
</tr>
<tr>
<td width="22%"><tt>support_modifiable_properties</tt></td>
<td width="18%"><tt>CORBA::Boolean</tt></td>
<td width="60%">Search considers offers with not readonly properties.</td>
</tr>
<tr>
<td width="22%"><tt>starting_trader</tt></td>
<td width="18%"><tt>CosTrading::TraderName</tt></td>
<td width="60%">Query is forwarded across all links in the policy, and search begins at
the final trader.</td>
</tr>
<tr>
<td width="22%"><tt>hop_count</tt></td>
<td width="18%"><tt>CORBA::ULong</tt></td>
<td width="60%">Maximum depth a query should be propagated in the trader federation.</td>
</tr>
<tr>
<td width="22%"><tt>link_follow_rule</tt></td>
<td width="18%"><tt>CosTrading::FollowOption</tt></td>
<td width="60%">Query propagates to other traders if the <tt>link_follow_rule</tt> permits
it.</td>
</tr>
</table>
<p>The TAO Trading Service comes with a handy utility --- <tt>TAO_Policy_Manager</tt> ---
for creating a policy sequence to pass to the query method that won't incur any
exceptions. Use the <tt>TAO_Policy_Manager</tt> in the following way:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>TAO_Policy_Manager policies;
policies.exact_type_match (CORBA::B_FALSE);
policies.search_card (16*NUM_OFFERS);
policies.match_card (16*NUM_OFFERS);
policies.return_card (16*NUM_OFFERS);
policies.link_follow_rule (CosTrading::local_only);
const CosTrading::PolicySeq& policy_seq = policies.policy_seq ();</pre>
</td>
</tr>
</table>
<h3><a name="FilteringProperties">Filtering Properties</a></h3>
<p>If the client wants only a subset of the properties defined for a service type returned
in matching offers, it can specify those property names in the <tt>desired_properties</tt>
parameter of the query method. Pass the <tt>prop_names</tt> method of <tt>CosTrading::Lookup::SpecifiedProperties</tt>
a <tt>CosTrading::PropNameSeq</tt>:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>char* props[] = {"Name", "Description", "Location", "Host_Name" };
CosTrading::Lookup::SpecifiedProps desired_props;
CosTrading::PropertyNameSeq prop_name_seq (4, 4, props, CORBA::B_FALSE);
desired_props.prop_names (prop_name_seq);</pre>
</td>
</tr>
</table>
<h3><a name="OfferIterators">Offer Iterators</a></h3>
<p>Those offers returned from the query in excess of <tt>how_many</tt> are placed in an
offer iterator for deferred retrieval. The <tt>CosTrading::OfferIterator::next_n</tt>
method will allocate a sequence and fill it with either n offers, or if it has fewer than <tt>n</tt>
offers, the remaining offers. The <tt>next_n</tt> method returns true if the iterator
contains more offers, and false if it's been depleted. After finishing with the iterator,
invoke its <tt>destroy</tt> method to release any server-side resources.</p>
<p>The following code is an example of obtaining offers from a <tt>CosTrading::OfferIterator</tt>:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>CORBA::Boolean any_left = CORBA::B_FALSE;
CORBA::Environment _env;</pre>
<pre>do
{
CosTrading::OfferSeq_ptr iter_offers_ptr;
CosTrading::OfferSeq_out iter_offers_out (iter_offers_ptr);
any_left = offer_iterator->next_n (length,
iter_offers_out,
_env);
TAO_CHECK_ENV_RETURN (_env, 0);
CosTrading::OfferSeq_var iter_offers (iter_offers_ptr);
// Process offers...
} while (any_left);</pre>
</td>
</tr>
</table>
<h3><a name="PropertyEvaluation">Property Evaluation</a></h3>
<p>After the client completes a query that used dynamic properties, to review the property
values of the returned offers, it has to distinguish between <tt>Anys</tt> containing
static properties and <tt>Anys</tt> containing dynamic property structures. The <tt>TAO_Property_Evaluator</tt>
class is a handy utility to obtain property values that hides how it evalutes properties
for the client --- by simple <tt>Any</tt> value extraction for static properties, or by
calling back to a dynamic property interface. The <tt>TAO_Property_Evaluator</tt> caches
the value of a dynamic property, and frees the allocated <tt>Anys</tt> during its
destruction. </p>
<p>The following code demonstrates how to use the <tt>TAO_Property_Evaluator</tt> to dump
the properties of an offer to the screen. </p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>TAO_Property_Evaluator prop_eval (prop_seq);
for (int length = prop_seq.length (), k = 0; k < length; k++)
{
ACE_DEBUG ((LM_DEBUG, "%-15s: ", prop_seq[k].name.in ()));
TAO_TRY
{
CORBA::Boolean is_dynamic = prop_eval.is_dynamic_property (k);
TAO_CHECK_ENV;
value = prop_eval.property_value(k, env);
TAO_CHECK_ENV;
if (value != 0)
CORBA::Any::dump (*value);
}
TAO_CATCHANY
{
ACE_DEBUG ((LM_DEBUG, "Error retrieving property value.\n"));
}
TAO_ENDTRY;
}</pre>
</td>
</tr>
</table>
<h2><a name="TheExporterRole">The Exporter Role --- Registering a Service Type and Offer</a></h2>
<p>Before an exporting client can register a new service offer with the Trading Service,
it needs to ensure first that its service type is present in the service type repository
of the target trader. The most efficient way to do this is to first invoke the <tt>export</tt>
method on the <tt>Register</tt> interface, and if it raises an <tt>UnknownServiceType</tt>
exception, obtain a reference to the Repository, add the Service Type, and attempt the <tt>export</tt>
a second time. Here's the boilerplate code:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>CORBA::Object_var trading_obj =
orb_ptr->resolve_initial_references ("TradingService");
CosTrading::Lookup_var lookup_if =
CosTrading::Lookup::_narrow (trading_obj.in (), _env);
TAO_CHECK_ENV_RETURN (_env, -1);
CosTrading::Register_var register_if = lookup_if->register_if (_env);
TAO_CHECK_ENV_RETURN (_env, -1);
CosTrading::TypeRepository_ptr obj = this->trader_->type_repos (_env);
CosTradingRepos::ServiceTypeRepository_var str =
CosTradingRepos::ServiceTypeRepository::_narrow (obj, _env);
TAO_CHECK_ENV_RETURN (_env, -1);
TAO_TRY
{
// Attempt to export the offer.
offer_id =
register_id->export (object_ref, type, props, TAO_TRY_ENV);
TAO_CHECK_ENV;
}
TAO_CATCH (CosTrading::UnknownServiceType, excp)
{
// If the ServiceTypeName wasn't found, we'll have to add the
// type to the Service Type repository ourselves.
str->add_type (type,
object_ref->_interface_repository_id (),
prop_struct_seq,
super_type_name_seq,
_env);
TAO_CHECK_ENV_RETURN (_env, 0);
// Now we'll try again to register the offer.
offer_id = reg->export (object_ref, type, this->tprops_, _env);
TAO_CHECK_ENV_RETURN (_env, 0);
TAO_TRY_ENV.clear ();
}
TAO_CATCHANY
{
// Sigh, all our efforts were for naught.
TAO_RETHROW_RETURN (0);
}
TAO_ENDTRY;</pre>
</td>
</tr>
</table>
<h3><a name="TheServiceTypeRepository">The Service Type Repository</a></h3>
<p>Creating a service type description is simply a matter of filling in two sequences: a <tt>CosTradingRepos::ServiceTypeRepository::PropStructSeq</tt>
and a <tt>CosTradingRepos::ServiceTypeRepository::ServiceTypeNameSeq</tt>. When filling in
the <tt>value_type</tt> field, remember to up the reference count of the <tt>TypeCode</tt>,
since otherwise the <tt>TypeCode_var</tt> will sieze control of the memory and free it.
Here's a code excerpt taken from <tt>export_test</tt> showing how to build the first
couple elements of such sequences:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>this->type_structs_[TT_Info::PLOTTER].props.length (2);
this->type_structs_[TT_Info::PLOTTER].super_types.length (1);
this->type_structs_[TT_Info::PLOTTER].super_types[0] =
TT_Info::INTERFACE_NAMES[TT_Info::REMOTE_IO];
this->type_structs_[TT_Info::PLOTTER].props[0].name =
TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_NUM_COLORS];
this->type_structs_[TT_Info::PLOTTER].props[0].value_type =
CORBA::TypeCode::_duplicate (CORBA::_tc_long);
this->type_structs_[TT_Info::PLOTTER].props[0].mode =
CosTradingRepos::ServiceTypeRepository::PROP_NORMAL;
this->type_structs_[TT_Info::PLOTTER].props[1].name =
TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_AUTO_LOADING];
this->type_structs_[TT_Info::PLOTTER].props[1].value_type =
CORBA::TypeCode::_duplicate (CORBA::_tc_boolean);
this->type_structs_[TT_Info::PLOTTER].props[1].mode =
CosTradingRepos::ServiceTypeRepository::PROP_READONLY;</pre>
</td>
</tr>
</table>
<h3><a name="ExportingWithdrawingandModifying">Exporting, Withdrawing, and Modifying
Service Offers</a></h3>
<p>Like with adding a Service Type, exporting an offer is just filling in the sequences.
For offers, of course, property values are passed, so this involves employing the <tt>Any</tt>
insertion operators. Here's a code exerpt from <tt>export_test</tt>:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>CosTrading::PropertySeq prop_seq (2);
prop_seq[0].name =
TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_NUM_COLORS];
prop_seq[0].value <<= ACE_static_cast (CORBA::Long, 256);
prop_seq[1].name =
TT_Info::PLOTTER_PROPERTY_NAMES[TT_Info::PLOTTER_AUTO_LOADING];
prop_seq[1].value <<= CORBA::Any::from_boolean (CORBA::B_TRUE);</pre>
</td>
</tr>
</table>
<p>The <tt>export_test</tt> returns a <tt>CosTrading::OfferId</tt> string, which is
required to perform the <tt>withdraw</tt> and <tt>modify</tt> operations on the exported
offer. <tt>withdraw</tt> requires that you simply pass the <tt>OfferId</tt> of the offer
to be withdrawn, while <tt>modify</tt> takes two additional sequences: a <tt>CosTrading::PropertyNameSeq</tt>
of property names to be removed from the offer, and a <tt>CosTrading::PropertySeq</tt> of
offers to be added or changed in the offer. </p>
<h3><a name="ImplementingDynamicProperties">Implementing Dynamic Properties</a></h3>
<p>To export an offer with a dynamic property:
<ul>
<li>inherit from the <tt>TAO_Dynamic_Property</tt> class and implement its <tt>DP_Eval</tt>
method; </li>
<li>create a <tt>CosTradingDynamic::DynamicProperty</tt> structure using the <tt>TAO_Dynamic_Property::construct_dynamic_prop</tt>
method; </li>
<li>insert the <tt>CosTradingDynamic::DynamicProperty</tt> in the value field of the
property. </li>
</ul>
<p>The following code, taken from the <tt>export_test</tt> example, illustrates this:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>// Step 1: Write the Dynamic Property callback handler.
class Simple_DP : public TAO_Dynamic_Property
{
public:
virtual CORBA::Any* evalDP (const char* name,
CORBA::TypeCode_ptr returned_type,
const CORBA::Any& extra_info,
CORBA::Environment& _env)
TAO_THROW_SPEC ((CosTradingDynamic::DPEvalFailure));
};
CORBA::Any*
Simple_DP::evalDP (const char* name,
CORBA::TypeCode_ptr returned_type,
const CORBA::Any& extra_info,
CORBA::Environment& _env)
TAO_THROW_SPEC ((CosTradingDynamic::DPEvalFailure))
{
CORBA::Any* return_value = 0;
ACE_NEW_RETURN (return_value, CORBA::Any, 0);
(*return_value) <<= ACE_static_cast (CORBA::ULong, ACE_OS::rand ());
return return_value;
}</pre>
<pre>// Step 2: Create the Dynamic Property
Simple_DP dp;
CORBA::Any extra_info;
CosTrading::PropertySeq prop_seq (1);
CosTrading::DynamicProp* dp_struct =
dp.construct_dynamic_prop ("prop_name",
CORBA::_tc_ulong,
extra_info);</pre>
<pre>// Step 3: Turn over the dynamic property to the propery value Any.
CORBA::Environment env;
prop_seq[0].name = "prop_name";
prop_seq[0].value.replace (CosTrading::_tc_DynamicProp,
dp_struct,
CORBA::B_TRUE,
env);
TAO_CHECK_ENV_RETURN (env, -1);</pre>
</td>
</tr>
</table>
<h2><a name="TheAdministratorRole">The Administrator Role --- Tweaking Policies and
Adjusting Links</a></h2>
<p>The trader can be configured remotely through two interfaces: the <tt>Admin</tt>
interface, for tweaking global policies, enabling and disabling interfaces, and dumping
the trader contents; and the <tt>Link</tt> interface, for attaching to and detaching from
other traders. </p>
<p>Adjusting policies is straightforward. Here's an example of setting the <tt>max_search_card</tt>
policy:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>// lookup_if returned from resolve_initial_references.
CosTrading::Admin_var admin_if =
lookup_if->admin_if (TAO_TRY_ENV);
TAO_CHECK_ENV;</pre>
<pre>admin_if->set_max_match_card (200);</pre>
</td>
</tr>
</table>
<p>Here's an example of using the list_offers method on the Admin interface to remove all
offers from the Trader:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>TAO_TRY
{
CosTrading::OfferIdIterator_ptr offer_id_iter;
CosTrading::OfferIdSeq_ptr offer_id_seq;
// lookup_if returned from resolve_initial_references.
CosTrading::Admin_var admin_if =
lookup_if->admin_if (TAO_TRY_ENV);
TAO_CHECK_ENV;
CosTrading::Register_var register_if =
lookup_if->register_if (TAO_TRY_ENV);
TAO_CHECK_ENV;
admin_if->list_offers (10,
CosTrading::OfferIdSeq_out (offer_id_seq),
CosTrading::OfferIdIterator_out (offer_id_iter),
TAO_TRY_ENV);
TAO_CHECK_ENV;
if (offer_id_seq != 0)
{
CosTrading::OfferIdSeq_var offer_id_seq_var (offer_id_seq);
for (CORBA::ULong i = 0; i < offer_id_seq_var.length (); i++)
{
register_if->withdraw (offer_id_seq_var[i], TAO_TRY_ENV);
TAO_CHECK_ENV;
}
}
if (offer_id_iter != CosTrading::OfferIdIterator::_nil ())
{
CORBA::Boolean any_left = CORBA::B_FALSE;
CosTrading::OfferIdSeq_ptr id_seq = 0;
CosTrading::OfferIdIterator_var offer_id_iter_var (offer_id_iter);
do
{
any_left =
offer_id_iter->next_n (length,
CosTrading::OfferIdSeq_out (id_seq),
TAO_TRY_ENV);
TAO_CHECK_ENV;
CORBA::ULong offers = id_seq->length ();
for (CORBA::ULong i = 0; i < offers; i++)
{
register_if->withdraw (id_seq[i], TAO_TRY_ENV);
TAO_CHECK_ENV;
}
delete id_seq;
}
while (any_left);
offer_id_iter->destroy (TAO_TRY_ENV);
TAO_CHECK_ENV;
}
}
TAO_CATCHANY
{
// Handle Errors.
}
TAO_ENDTRY;</pre>
</td>
</tr>
</table>
<p>Here's an example a trader linking itself to another trader (<tt>this->trader_</tt>
is a colocated trader --- see the next section for more information): </p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>TAO_TRY
{
CosTrading::Link_var link_if = lookup_if->link_if (TAO_TRY_ENV);
TAO_CHECK_ENV;
TAO_Trading_Components_Impl& trd_comp =
this->trader_->trading_components ();
CosTrading::Lookup_ptr our_lookup = trd_comp.lookup_if ();
CosTrading::Link_ptr our_link = trd_comp.link_if ();
link_if->add_link (this->name_.in (),
our_lookup,
CosTrading::always,
CosTrading::always,
TAO_TRY_ENV);
TAO_CHECK_ENV;
our_link->add_link ("Bootstrap_Trader",
lookup_if.in (),
CosTrading::always,
CosTrading::always,
TAO_TRY_ENV);
}
TAO_CATCHANY
{
// Handle Errors.
}
TAO_ENDTRY;</pre>
</td>
</tr>
</table>
<hr>
<h1><a name="TheServerRole">The Server Role</a></h1>
<p>The TAO Trading Service comes with an out-of-the-box executable suitable for common
use. However, it can also easily be colocated with any other TAO server to add Trading
Service functionality to that server.</p>
<h2><a name="TheTAOTradingServiceApplication">The TAO Trading Service Application</a></h2>
<p>This out-of-the-box server takes a number of command line arguments:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="26%"><tt>-TSthreadsafe</tt></td>
<td width="74%">The Trader will use reader/writer locks to protect the offer database and
link collection, and normal thread mutexes for the rest of the shared state --- global
policies, support attributes, and interface accessors. (default is not thread safe; Null
Mutexes are used)</td>
</tr>
<tr>
<td width="26%"><tt>-TSconformance</tt></td>
<td width="74%">Determines which conformance category the Trading Service will meet:<br>
<table border="0" width="100%" cellpadding="3">
<tr>
<td width="18%"><ul>
<li><em>query</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt> interface only</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>simple</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt> and <tt>Register</tt>
interfaces</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>standalone</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt>, <tt>Register</tt>,
and <tt>Admin</tt> interfaces</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>linked</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Instantiates the <tt>Lookup</tt>, <tt>Register</tt>,
<tt>Admin</tt>, and <tt>Link</tt> interfaces (default)</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="26%"><tt>-TSsupports_dynamic_properties</tt></td>
<td width="74%"><table border="0" width="100%" cellpadding="3">
<tr>
<td width="18%"><ul>
<li><em>true</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Will consider offers with dynamic properties in
queries unless explicitly disabled by a policy passed to the query method. (default)</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>false</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Will not consider offers with dynamic properties
in queries, unless explicitly enabled by a policy passed to the query method.</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="26%"><tt>-TSsupports_modifiable_properties</tt></td>
<td width="74%"><table border="0" width="100%" cellpadding="3">
<tr>
<td width="18%"><ul>
<li><em>true</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Will consider offers with not explicitly
modifable properties in queries unless explicitly disabled by a policy passed to the query
method. Enables the <tt>modify</tt> method on the <tt>Register</tt> interface. (default)</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>false</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">Will not consider dynamic properties in queries,
unless explicitly overridden by a query policy. Diables <tt>modify</tt> method on the <tt>Register</tt>
interface.</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="26%"><tt>-TSdef_search_card</tt></td>
<td width="74%">Search cardinality if none is specified as a query policy. (default is
200)</td>
</tr>
<tr>
<td width="26%"><tt>-TSmax_search_card</tt></td>
<td width="74%">Upper limit on the search cardinality for a query. (default is 500)</td>
</tr>
<tr>
<td width="26%"><tt>-TSdef_match_card</tt></td>
<td width="74%">Match cardinality if none is specified as a query policy. (default is 200)</td>
</tr>
<tr>
<td width="26%"><tt>-TSmax_match_card</tt></td>
<td width="74%">Upper limit on the match cardinality for a query. (default is 500)</td>
</tr>
<tr>
<td width="26%"><tt>-TSdef_return_card</tt></td>
<td width="74%">Return cardinality if none is specified as a query policy. (default is
200)</td>
</tr>
<tr>
<td width="26%"><tt>-TSmax_return_card</tt></td>
<td width="74%">Upper limit on the return cardinality for a query. (default is 500)</td>
</tr>
<tr>
<td width="26%"><tt>-TSdef_hop_count</tt></td>
<td width="74%">The depths a federated query may go if no query policy is specified.
(default 5)</td>
</tr>
<tr>
<td width="26%"><tt>-TSmax_hop_count</tt></td>
<td width="74%">The maximum number of links a federated query can travel after it passes
through this trader. (default is 10) </td>
</tr>
<tr>
<td width="26%"><tt>-TSdef_follow_policy</tt></td>
<td width="74%"><table border="0" width="100%" cellpadding="3">
<tr>
<td width="18%"><ul>
<li><em>always</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader will always pass a query onto the
next available linked trader.</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>if_no_local</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader will pass a query onto the next
trader only if the local search produced no results. (default)</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>local_only</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader will never pass on a query.</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="26%"><tt>-TSmax_follow_policy</tt></td>
<td width="74%"><table border="0" width="100%" cellpadding="3">
<tr>
<td width="18%"><ul>
<li><em>always</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader doesn't limit the importer to the
local offer space. (default)</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>if_no_local</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader refuses to pass on queries of the
local search matched offers.</td>
</tr>
<tr>
<td width="18%"><ul>
<li><em>local_only</em></li>
</ul>
</td>
<td width="82%" valign="top" align="left">The trader will never allow federated queries.</td>
</tr>
</table>
</td>
</tr>
<tr>
<td width="26%"><tt>-ORBtradingserviceport</tt></td>
<td width="74%">Port on which to listen for multicast bootstrap requests.</td>
</tr>
</table>
<p>By default the trader will listen for multicast <tt>resolve_initial_references</tt>
requests, and respond with the IOR of its <tt>Lookup</tt> inteface. For the purposes of
testing federated queries, when passed the <tt>-TSfederate</tt> method, instead of
becoming a bootstrappable server, the <tt>Trading_Service</tt> application will bootstrap
itself to a multicast trader, link itself to that trader and every other trader accessible
through that trader. This protocol will have all traders on the multicast network form a
complete graph. </p>
<h2><a name="ColocatingtheTradingServiceinaTAOApplication">Colocating the Trading Service
in a TAO Application</a></h2>
<p>Colocating the Trading Service in a TAO application amounts to constructing a <tt>TAO_TRADER</tt>
object using the <tt>TAO_Trader_Factory::construct_trader</tt> call. The <tt>argc</tt> and
<tt>argv</tt> parameters to <tt>construct_trader</tt> contain the configuration parameters
described in the previous section. The trader is also configurable programatically through
its attribute classes. The follow code exerpt demonstrates this. </p>
<p>In addition the application will need to create a service type repository
implementation --- TAO's being the <tt>TAO_Service_Type_Repository</tt> --- and configure
the trader with it. The service type repository is separate from the trader in this way to
allow, for example, multiple traders to share the same service type repository. The
following code exerpt also demontrates configuring the repository:</p>
<table border="1" width="100%" cellpadding="3">
<tr>
<td width="100%"><pre>TAO_TRADER* trader = TAO_Trader_Factory::create_trader (argc, argv);
TAO_Support_Attributes_Impl& sup_attr = trader->support_attributes ();
TAO_Import_Attributes_Impl& imp_attr = trader->trading_components ();
// Configure the trader with a service type repository.
CORBA::Environment _env;
TAO_Service_Type_Repository type_repos* type_repos = 0;
ACE_NEW (type_repos, TAO_Service_Type_Repository);
sup_attr.type_repos (type_repos->_this (_env));
TAO_CHECK_ENV_RETURN (_env, -1);</pre>
<pre>// Configure other policies, overriding the command line arguments.
imp_attr.search_card (20);
sup_attr.supports_dynamic_properties (CORBA::B_FALSE);</pre>
</td>
</tr>
</table>
<p>The trader interfaces register themselves with the default POA during the Trading
Service's construction. All that remains is to activate the POA and enter the ORB event
loop. </p>
<hr>
<h1><a name="RunningtheTradingServiceTests">Running the Trading Service Tests</a></h1>
<p>There are two executables that test the Trading Service funtionality --- one to test
the exporter role, and the other, the importer role. To run the tests simply launch the <tt>Trading_Service</tt>
application, then run the <tt>export_test</tt> executable found in the <tt>orbsvcs/tests/Trading</tt>
directory. When the <tt>export_test</tt> ceases to output data and enters the event loop,
run the <tt>import_test</tt> found in the same directory. </p>
<p><strong>Note: </strong>The export_test and the Trading_Service executables are servers
--- the export_test is a server of dynamic properties. Hence, if you run both executables
on the same machine, you must supply them with different ports. For example, add -ORBport
0 to the export_test command line. </p>
<p>To test federated queries, run at least three copies of the <tt>Trading_Service</tt>
application, each using the <tt>-TSfederate</tt> flag. The traders will form a complete
graph, with each link follow policy set to <tt>CosTrading::always</tt>. When run with the <tt>-f</tt>
flag, the <tt>export_test</tt> will add the service types and export offers to each of the
traders in the federation. When run with the <tt>-f</tt> flag, the <tt>import_test </tt>will
perform a directed query to a trader two links distant from the trader boostrapped to, in
addition to performing federated queries. </p>
<p>By default the tests dump the contents of service types and offers to the screen so the
tester can validate the results. To run the tests in quiet mode, where the results of the
describe and query methods are concealed, use the <tt>-q</tt> flag.</p>
<hr>
<h1><a name="KnownBugsandWorkarounds">Known Bugs and Workarounds</a></h1>
<p>At this point there are no known problems with TAO that affect the
Trading service.</p>
<hr>
<h1><a name="FutureWork">Future Work</a></h1>
<ul>
<li><strong>Persistence</strong> --- Have the Trading Service offer database and service
type repository survive the lifetime of a single Trading Service process. This would be
accomplished by either taking advantage of the ability to serialize IDL types --- using
CDR streams --- or through memory-mapped files, <em>a la </em>the ACE Naming Service.</li>
</ul>
<ul>
<li><strong>The <tt>Proxy</tt> Interface </strong>--- Should we ever feel so motivated, we
might implement the <tt>Proxy</tt> interface. </li>
</ul>
<hr>
<address>
<a href="mailto:sbw1@cs.wustl.edu">Seth Benjamin Widoff</a>
</address>
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