Request-Reply Examples

Examples on how to use the request-reply API. More...

Examples on how to use the request-reply API.

Request-Reply code examples.

Request-Reply Examples

DDS Types

RTI Connext uses DDS data types for sending and receiving requests and replies. Valid types are those generated by the rtiddsgen code generator, the DDS built-in types, and DynamicData. Refer to the User's Manual and the following links for more information:

• Creating user data types using rtiddsgen,

• Using the DDS built-in types,

• Using DynamicData

Set up

• Create a DomainParticipant

• Create a requester

• Create a requester with parameters

• Create a replier

Requester: sending requests and receiving replies

• Basic Requester example

  • Correlation between requests and replies

Replier: receiving requests and sending replies

• SimpleReplier example

• Basic Replier example

Requester Creation

• Setting up a DomainParticipant

• Creating a Requester

      using namespace rti::request;
  
      dds::domain::DomainParticipant participant(domain_id);
  
      Requester<Foo, Bar> requester(participant, "TestService");
  

Creating a Requester with optional parameters

• Setting up a DomainParticipant

• Creating a Requester with additional parameters

      using namespace rti::request;
  
      // Create a DomainParticipant
      dds::domain::DomainParticipant participant(domain_id);
  
      // Create a Requester with a QoS profile (located for example in
      // USER_QOS_PROFILES.xml, in the current working directory, which the
      // default QosProvider will load)
      RequesterParams requester_params(participant);
      requester_params.service_name("TestService");
  
      dds::core::QosProvider qos_provider = dds::core::QosProvider::Default();
      requester_params.datareader_qos(
              qos_provider.datareader_qos("RequestReplyExampleProfiles::RequesterExampleProfile"));
      requester_params.datawriter_qos(
              qos_provider.datawriter_qos("RequestReplyExampleProfiles::RequesterExampleProfile"));
  
  
      Requester<Foo, Bar> requester(requester_params);
  

  See Also

  Requester Creation

  Configuring Request-Reply QoS profiles

Basic Requester example

• Requester Creation
• Creating a Requester with optional parameters

• Basic Requester example

      using namespace rti::request;
  
      // Send request
      Foo request("A Request");
      requester.send_request(request);
  
      // Receive reply (wait for it and get the sample)
      auto replies = requester.receive_replies(MAX_WAIT);
  
      if (replies.length() == 0) {
          std::cout << "Reply not received\n";
      }
  
      for (const auto& reply : replies) {
          if (reply.info().valid()) {
              std::cout << "Received reply: " << reply.data() << std::endl;
          } else {
              std::cout << "Received invalid reply\n";
          }
      }
  

  See Also

  Basic Replier example

  SimpleReplier example

Correlating requests and replies

• Requester Creation

• Example 1) Waiting for a reply to a specific request

  
      using namespace rti::request;
  
      // Create requests
      Foo request1("Request 1"), request2("Request 2");
  
      // Send requests and save request ID
      rti::core::SampleIdentity request_id1 = requester.send_request(request1);
      rti::core::SampleIdentity request_id2 = requester.send_request(request2);
  
      // Wait for a reply to the second request
      bool received = requester.wait_for_replies(1, MAX_WAIT, request_id2);
  
      if (!received) {
          std::cout << "Did not receive reply for request 2" << std::endl;
          return;
      }
  
      // Take that reply
      dds::sub::LoanedSamples<Bar> replies = requester.take_replies(request_id2);
      if (replies.length() == 0) {
          throw std::runtime_error("did not receive any replies");
      }
  
      // This postcondition should always be true
      if (replies[0].info()->related_original_publication_virtual_sample_identity()
              != request_id2) {
          throw std::runtime_error("postcondition failed");
      }
  
      if (replies[0].info().valid()) {
          std::cout << "Received reply for request 2: "
                    << replies[0].data() << std::endl;
      }
  
      // Wait for a reply to the first request
      received = requester.wait_for_replies(1, MAX_WAIT, request_id1);
  
      if (!received) {
          std::cout << "Did not receive reply for request 1" << std::endl;
          return;
      }
  
      // Take that reply
      replies = requester.take_replies(request_id1);
      if (replies.length() == 0) {
          throw std::runtime_error("did not receive any replies");
      }
  
      // This postcondition should always be true
      if (replies[0].info()->related_original_publication_virtual_sample_identity()
              != request_id1) {
          throw std::runtime_error("postcondition failed");
      }
  
      if (replies[0].info().valid()) {
          std::cout << "Received reply for request 1: "
                    << replies[0].data() << std::endl;
      }
  

• Example 2) Correlating a reply after receiving it

  
      using namespace rti::request;
  
      // Create requests
      Foo request1("Request 1"), request2("Request 2");
  
      // Send requests and save request ID
      rti::core::SampleIdentity request_id1 = requester.send_request(request1);
      rti::core::SampleIdentity request_id2 = requester.send_request(request2);
  
      // Wait for two replies. In this case we don't mind the
      // reception order
      bool received = requester.wait_for_replies(2, MAX_WAIT);
      if (!received) {
          std::cout << "Replies not received" << std::endl;
          return;
      }
  
      // Get all the replies
      auto replies = requester.take_replies();
  
      // Find the reply for request 1.
      //
      // We search using the STL find_if algorithm. The search range is all
      // the elements in the replies container (from beginning to end).
      // We use a predicate included in the API that evaluates to
      // true when a Sample's related_identity equals the identity that
      // is passed to the constructor (request_id1, in this case)
      auto it = std::find_if(
              replies.begin(),
              replies.end(),
              IsReplyRelatedPredicate<Bar>(request_id1));
  
      if (it != replies.end()) {
          std::cout << "Received reply for request 1: "
                    << it->data() << std::endl;
      }
  
      // Find the reply for request 2
      it = std::find_if(
              replies.begin(),
              replies.end(),
              IsReplyRelatedPredicate<Bar>(request_id2));
  
      if (it != replies.end()) {
          std::cout << "Received reply for request 2: "
                    << it->data() << std::endl;
      }
  

  See Also

  Basic Requester example

  Basic Replier example

Creating a Replier

• Setting up a DomainParticipant

• Create a Replier

      using namespace rti::request;
  
      dds::domain::DomainParticipant participant(domain_id);
  
      // Use the same service name as the Requester's
      Replier<Foo, Bar> replier(participant, "TestService");
  

Basic Replier example

• Creating a Replier

• Basic Replier example

  
      using namespace rti::request;
  
      // Receive requests
      dds::sub::LoanedSamples<Foo> requests = replier.receive_requests(MAX_WAIT);
      for (const auto& request : requests) {
          if (!request.info().valid()) {
              continue;
          }
  
          Bar reply("Reply for " + request.data().message());
  
          // Send a reply for this request, identified by the ID in
          // request.info()
          replier.send_reply(reply, request.info());
  
          // Note: a replier can send more than one reply for the same request
          // replier.send_reply(Bar("Another reply"), request.info());
      }
  

  See Also

  Basic Requester example

SimpleReplier example

    using namespace rti::request;

    SimpleReplier<Foo, Bar> replier(
        participant,
        "TestService",
        [](const Foo& request)
        {
            return Bar(std::string("Simple reply for ") + request.message());
        }
    );

    // After creation the SimpleReplier is already active and the functor will
    // be called upon receiving a request.

See Also

Basic Requester example

Configuring Request-Reply QoS profiles

If you do not specify your own QoS parameters (in RequesterParams and ReplierParams), a rti::request::Requester and rti::request::Replier are created using a default configuration. That configuration is equivalent to the one in the following QoS profile called "default":

<?xml version="1.0"?>
<!-- 
Description
XML QoS Profile for ExampleRequest

The QoS configuration of the DDS entities in the generated example is loaded 
from this file.

This file is used only when it is in the current working directory or when the
environment variable NDDS_QOS_PROFILES is defined and points to this file.

The profile in this file inherits from the builtin QoS profile 
BuiltinQosLib::Generic.StrictReliable. That profile, along with all of the 
other built-in QoS profiles can be found in the 
BuiltinProfiles.documentationONLY.xml file located in the 
$NDDSHOME/resource/xml/ directory.

You may use any of these QoS configurations in your application simply by 
referring to them by the name shown in the 
BuiltinProfiles.documentationONLY.xml file and listed below: 

* In library "BuiltinQosLib":
** Baseline
** Baseline.5.0.0
** Baseline.5.1.0
** Baseline.5.2.0
** Generic.Common
** Generic.510TransportCompatibility
** Generic.Monitoring.Common
** Generic.ConnextMicroCompatibility
** Generic.OtherDDSVendorCompatibility

* In library "BuiltinQosLibExp":
** Generic.StrictReliable
** Generic.KeepLastReliable
** Generic.BestEffort
** Generic.StrictReliable.HighThroughput
** Generic.StrictReliable.LowLatency
** Generic.Participant.LargeData
** Generic.Participant.LargeData.Monitoring
** Generic.StrictReliable.LargeData
** Generic.KeepLastReliable.LargeData
** Generic.StrictReliable.LargeData.FastFlow
** Generic.StrictReliable.LargeData.MediumFlow
** Generic.StrictReliable.LargeData.SlowFlow
** Generic.KeepLastReliable.LargeData.FastFlow
** Generic.KeepLastReliable.LargeData.MediumFlow
** Generic.KeepLastReliable.LargeData.SlowFlow
** Generic.KeepLastReliable.TransientLocal
** Generic.KeepLastReliable.Transient
** Generic.KeepLastReliable.Persistent
** Generic.AutoTuning
** Pattern.PeriodicData
** Pattern.Streaming
** Pattern.ReliableStreaming
** Pattern.Event
** Pattern.AlarmEvent
** Pattern.Status
** Pattern.AlarmStatus
** Pattern.LastValueCache

You should not edit the file BuiltinProfiles.documentationONLY.xml directly.
However, if you wish to modify any of the values in a built-in profile, the
recommendation is to create a profile of your own and inherit from the built-in
profile you wish to modify. The NDDS_QOS_PROFILES.example.xml file (contained in 
the same directory as the BuiltinProfiles.documentationONLY.xml file) shows how
to inherit from the built-in profiles. 

For more information about XML QoS Profiles see Chapter 17 in the 
RTI Connext user manual.
-->
<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="/home/build3/rti/waveworks/ndds531/connextdds/ndds.4.1/resource/schema/rti_dds_qos_profiles.xsd"
     version="5.3.1">
    <!-- QoS Library containing the QoS profile used in the generated example.

        A QoS library is a named set of QoS profiles.
    -->
    <qos_library name="ExampleRequest_Library">

        <!-- QoS profile used to configure reliable communication between the DataWriter 
             and DataReader created in the example code.

             A QoS profile groups a set of related QoS.
        -->
        <qos_profile name="ExampleRequest_Profile" base_name="BuiltinQosLibExp::Generic.StrictReliable" is_default_qos="true">
            <!-- QoS used to configure the data writer created in the example code -->                
            <datawriter_qos>
                <publication_name>
                    <name>ExampleRequestDataWriter</name>
                </publication_name>
                <!-- This property is needed when using -unboundedSupport command-line option
                 in order to configure the memory allocation policy for the buffers that are
                 used to serialize the samples -->                
                <property>
                    <value>
                        <element>
                           <name>
                           dds.data_writer.history.memory_manager.fast_pool.pool_buffer_max_size
                           </name>
                           <value>4096</value>
                        </element>
                    </value>
                </property>
            </datawriter_qos>

            <!-- QoS used to configure the data reader created in the example code -->                
            <datareader_qos>
                <subscription_name>
                    <name>ExampleRequestDataReader</name>
                </subscription_name>
                <!-- This property is needed when using -unboundedSupport command-line option
                in order to configure the memory allocation policy for the buffers that are 
                used to keep the serialized keys for the instances -->        
                <property>
                    <value>
                        <element>
                            <name>
                            dds.data_reader.history.memory_manager.fast_pool.pool_buffer_max_size
                            </name>
                            <value>4096</value>
                        </element>
                    </value>
               </property>
            </datareader_qos>
            <participant_qos>
                <!--
                The participant name, if it is set, will be displayed in the
                RTI tools, making it easier for you to tell one
                application from another when you're debugging.
                -->
                <participant_name>
                    <name>ExampleRequestParticipant</name>
                    <role_name>ExampleRequestParticipantRole</role_name>
                </participant_name>

            </participant_qos>
        </qos_profile>

    </qos_library>
</dds>

You can use the profile called "RequesterExampleProfile", which modifies some parameters from the default. The example Creating a Requester with optional parameters shows how to create a rti::request::Requester using this profile.

See Also

Creating a Requester with optional parameters

Configuring QoS Profiles with XML