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

• Taking loaned samples

• Taking samples by copy

• Correlation between requests and replies

Replier: receiving requests and sending replies

• SimpleReplier example

• Basic Replier example

• Taking loaned samples

• Taking samples by copy

Error handling

• Error handling example

Creating a Requester

• Setting up a participant

• Creating a Requester

  
              // Note: error checking omitted for simplicity
  
              // Create a DomainParticipant
              DomainParticipant participant =
                  DomainParticipantFactory.get_instance().create_participant(
                      domainId, DomainParticipantFactory.PARTICIPANT_QOS_DEFAULT,
                      null, StatusMask.STATUS_MASK_NONE);
  
              // Create a Requester (if creation fails an exception is thrown)
              // Foo is the request type and FooTypeSupport is its DDS TypeSupport
              // Bar is the reply type and BarTypeSupport is its DDS TypeSupport
              Requester<Foo, Bar> requester =
                  new Requester<Foo, Bar>(
                          participant, "TestService",
                          FooTypeSupport.get_instance(),
                          BarTypeSupport.get_instance());
  

• Finalizing a Requester

              // A Requester is IDisposable
              requester.Dispose();

  See Also

  Creating a Requester with optional parameters

  Configuring Request-Reply QoS profiles

Creating a Requester with optional parameters

• Setting up a participant

• Creating a Requester with optional parameters

  
              // Note: error checking omitted for simplicity
  
              // Create a DomainParticipant
              DomainParticipant participant =
                  DomainParticipantFactory.get_instance().create_participant(
                          0, DomainParticipantFactory.PARTICIPANT_QOS_DEFAULT,
                          null, StatusMask.STATUS_MASK_NONE);
  
              // Create a Requester with a QoS profile (located for example in
              // USER_QOS_PROFILES.xml, in the current working directory)
              Requester<Foo, Bar> requester =
                  new Requester<Foo, Bar>(
                      new RequesterParams(
                          participant,
                          FooTypeSupport.get_instance(),
                          BarTypeSupport.get_instance())
                      .SetServiceName("TestService")
                      .SetQosProfile("RequestReplyExampleProfiles",
                                     "RequesterExampleProfile"));
  

  See Also

  Creating a Requester

Basic Requester example

• Creating a Requester
• Creating a Requester with optional parameters

• Basic Requester example

  
              // Send request
              Foo request = new Foo();
              request.message = "A request";
              requester.SendRequest(request);
  
              // Create reply Sample
              Sample<Bar> reply = requester.CreateReplySample();
  
              // Receive reply (wait for it and get the sample)
              bool received = requester.ReceiveReply(reply, MAX_WAIT);
  
              if (received)
              {
                  if (reply.Info.valid_data)
                  {
                      Console.WriteLine("Received reply: " + reply.Data.message);
                  }
                  else
                  {
                      Console.WriteLine("Received invalid reply");
                  }
              }
              else
              {
                  Console.WriteLine("Reply not received");
              }
  

• Basic Requester example using the String built-in type

  
              // Create a requester using the String 
              // type with the DDS StringTypeSupport. The actual
              // type is StringWrapper
              Requester<StringWrapper, StringWrapper> requester =
                  new Requester<StringWrapper, StringWrapper>(
                      participant, "TestServiceString",
                      StringTypeSupport.get_instance(),
                      StringTypeSupport.get_instance());
  
              // Send request
              // Conversions between StringWrapper and String are supported
              requester.SendRequest("A request");
  
              // Create reply Sample
              Sample<StringWrapper> reply = requester.CreateReplySample();
  
              // Receive reply (wait for it and get the sample)
              bool received = requester.ReceiveReply(reply, MAX_WAIT);
  
              if (received && reply.Info.valid_data)
              {
                  Console.WriteLine("Received reply: " + reply.Data);
              }
  

• Basic Requester example using DynamicData.

  
              // Instantiate DynamicData type support. For simplicity we create them
              // from existing, generated TypeCode objects (Foo and Bar)
              DynamicDataTypeSupport fooDynamicTypeSupport =
                  new DynamicDataTypeSupport(
                      Foo.get_typecode(), new DynamicDataTypeProperty_t());
              DynamicDataTypeSupport barDynamicTypeSupport =
                  new DynamicDataTypeSupport(
                      Bar.get_typecode(), new DynamicDataTypeProperty_t());
  
              // Create a requester using a DynamicData type support
              Requester<DynamicData, DynamicData> requester =
                  new Requester<DynamicData, DynamicData>(
                      participant, "TestService",
                      fooDynamicTypeSupport,
                      barDynamicTypeSupport);
  
              // Create a Foo instance
              DynamicData foo = (DynamicData)fooDynamicTypeSupport.create_data();
              foo.set_string("message", DynamicData.MEMBER_ID_UNSPECIFIED,
                      "A dynamic request");
  
              // Send request
              requester.SendRequest(foo);
  
              // Create reply Sample
              Sample<DynamicData> reply = requester.CreateReplySample();
  
              // Receive reply (wait for it and get the sample)
              bool received = requester.ReceiveReply(reply, MAX_WAIT);
  
              if (received && reply.Info.valid_data)
              {
                  Console.WriteLine("Received reply: " +
                      reply.Data.get_string("message",
                          DynamicData.MEMBER_ID_UNSPECIFIED));
              }
  

  See Also

  Basic Replier example

Taking loaned samples

• Get iterator to loaned replies (no copies)

  
              // Take loaned samples
              // Unlike ReceiveReplies(), TakeReplies()  doesn't block. It returns an
              // empty collection if there are no replies at that moment.
              // (before that we can call requester.wait_for_replies)
              //
              // LoanedSamples is IDisposable, so the loan is automatically returned
              // to the middleware when the application exits the using block.
              using (LoanedSamples<Bar> replies = requester.TakeReplies())
              {
                  foreach (Sample<Bar> reply in replies)
                  {
                      Console.WriteLine("Received: " + reply.Data.message);
                  }
              }
  

  See Also

  Basic Requester example

  Basic Replier example

  Taking samples by copy

Taking samples by copy

• Get copies of the replies:

  
              List<Sample<Bar>> replies = new List<Sample<Bar>>();
  
              // Add to existing list, reusing and overwriting any existing elements
              requester.TakeReplies(replies, 10);
  
  
              foreach (Sample<Bar> reply in replies)
              {
                  Console.WriteLine("Received: " + reply.Data.message);
              }
  
              // Get replies in a newly created IList
              IList<Sample<Bar>> newList = requester.TakeReplies(null, 10);
              foreach (Sample<Bar> reply in newList)
              {
                  Console.WriteLine("Received: " + reply.Data.message);
              }
  

  See Also

  Basic Replier example

  Taking loaned samples

Correlating requests and replies

• Creating a Requester

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

  
              // Create requests
              WriteSample<Foo> request1 = requester.CreateRequestSample();
              request1.Data.message = "Request 1";
              WriteSample<Foo> request2 = requester.CreateRequestSample();
              request2.Data.message = "Request 2";
  
              // Send requests using WriteSample
              requester.SendRequest(request1);
              requester.SendRequest(request2);
  
              // Wait for a reply to the second request
              Console.WriteLine("Waiting for reply to request2");
              Sample<Bar> reply = requester.CreateReplySample();
              requester.WaitForReplies(1, MAX_WAIT, request2.Identity);
              requester.TakeReply(reply, request2.Identity);
  
              Debug.Assert(
                  reply.RelatedIdentity.Equals(request2.Identity));
              Console.WriteLine("Received reply: " + reply.Data.message);
  
              // Wait for a reply to the first request
              Console.WriteLine("Waiting for reply to request1");
              requester.WaitForReplies(1, MAX_WAIT, request1.Identity);
              requester.TakeReply(reply, request1.Identity);
  
              Debug.Assert(
                  reply.RelatedIdentity.Equals(request1.Identity));
              Console.WriteLine("Received reply: " + reply.Data.message);
  

• Example 2) Correlate reply after receiving it

  
              // Create requests
              WriteSample<Foo> request1 = requester.CreateRequestSample();
              request1.Data.message = "Request 1";
              WriteSample<Foo> request2 = requester.CreateRequestSample();
              request2.Data.message = "Request 2";
  
              // Send requests using WriteSample
              requester.SendRequest(request1);
              requester.SendRequest(request2);
  
              // Wait for two replies
              bool received = requester.WaitForReplies(2, MAX_WAIT);
              if (!received)
              {
                  Console.WriteLine("Replies not received");
                  return;
              }
  
  
              using (LoanedSamples<Bar> replies = requester.TakeReplies())
              {
                  foreach (Sample<Bar> reply in replies)
                  {
                      if (reply.RelatedIdentity.Equals(request1.Identity))
                      {
                          Console.WriteLine(
                              "Received reply for request 1: " + reply.Data.message);
                      }
                      else if (reply.RelatedIdentity.Equals(request2.Identity))
                      {
                          Console.WriteLine(
                              "Received reply for request 2: " + reply.Data.message);
                      }
                      else
                      {
                          // Should not happen
                          Console.WriteLine("Received unexpected reply");
                      }
                  }
              }
  

  See Also

  Basic Requester example

  Basic Replier example

Creating a Replier

• Setting up a participant

• Creating a Replier

  
              // Create a DomainParticipant
              DomainParticipant participant =
                  DomainParticipantFactory.get_instance().create_participant(
                      domain_id, DomainParticipantFactory.PARTICIPANT_QOS_DEFAULT,
                      null, StatusMask.STATUS_MASK_NONE);
  
              // Create a Requester
              Replier<Foo, Bar> replier = new Replier<Foo, Bar>(
                  participant, "TestService",
                  FooTypeSupport.get_instance(),
                  BarTypeSupport.get_instance());
  

• Finalizing a Replier

              // A Replier is IDisposable
              replier.Dispose();

Basic Replier example

• Creating a Replier

• Basic Replier example

  
              // Create a Sample for reading
              Sample<Foo> request = replier.CreateRequestSample();
  
              // Receive one request
              bool received = replier.ReceiveRequest(request, MAX_WAIT);
  
              if (!received)
              {
                  Console.WriteLine("Request not received");
                  return false;
              }
  
              if (request.Info.valid_data)
              {
                  // Send a reply for that request
                  Bar reply = new Bar();
                  reply.message = "Reply for " + request.Data.message;
                  replier.SendReply(reply, request.Identity);
              }
  
              // Note: a replier can send more than one reply for the same request
  

  See Also

  Basic Requester example

SimpleReplier example

• Implement a listener

          class MySimpleReplierListener : SimpleReplierListener<Foo, Bar>
          {
  
              private Bar reply = new Bar();
  
              public Bar OnRequestAvailable(Sample<Foo> request)
              {
                  if (request.Info.valid_data)
                  {
                      // Return a reply
                      reply.message = "Simple reply for " + request.Data.message;
                      return reply;
                  }
                  else
                  {
                      // Do not reply to dispose/unregister samples
                      return null;
                  }
              }
  
              public void ReturnLoan(Bar reply)
              {
                  // nothing to do
              }
  
          }

• And create a SimpleReplier with the listener:

  
              // Create a SimpleReplier using a DomainParticipant, service name and
              // the a SimpleReplierListener implementation
              SimpleReplier<Foo, Bar> replier =
                  new SimpleReplier<Foo, Bar>(
                      participant, "TestService",
                      new MySimpleReplierListener(),
                      FooTypeSupport.get_instance(),
                      BarTypeSupport.get_instance());
  
              // After creation the SimpleReplier is already active and may call
              // the listener
  

  See Also

  Basic Requester example

Error handling example

• Catching an exception from the request-reply API

  
              // All the operations in the request-reply API
              // throw exceptions in case of error.
  
              // You can also set the verbosity level to warning for
              // additional information
              NDDS.ConfigLogger.get_instance().set_verbosity(
                  NDDS.LogVerbosity.NDDS_CONFIG_LOG_VERBOSITY_WARNING);
  
  
              //
              // For example, this replier is sending a reply for a nonexistent request
              //
              WriteSample<Bar> reply = replier.CreateReplySample();
              SampleIdentity_t invalidRequestId = new SampleIdentity_t();
  
  
              try
              {
                  replier.SendReply(reply, invalidRequestId);
              }
              catch (Retcode_BadParameter ex)
              {
                  // You can also catch Retcode_Error, which is more generic
                  Console.WriteLine("Exception while sending reply: " + ex);
              }
  

Configuring Request-Reply QoS profiles

If you do not specify your own quality of service parameters (in RTI::Connext::RequestReply::RequesterParams and RTI::Connext::RequestReply::ReplierParams<TReq,TRep>), a RTI::Connext::RequestReply::Requester<TReq,TRep> and RTI::Connext::RequestReply::Replier<TReq,TRep> are created using a default configuration. That configuration is equivalent to the one in the following QoS profile called "default":

<?xml version="1.0"?>

<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="../../../resource/schema/rti_dds_qos_profiles.xsd"
    version="5.2.0">

    <qos_library name="RequestReplyExampleProfiles">
    
        <!-- Default QoS:
             
             This profile contains the QoS that Requesters and Repliers 
             would use by default. We can use it as a base profile to inherit
             from and override some parameters 
         -->
        <qos_profile name="default">
            <datawriter_qos>
            
                <!-- Strict reliable -->
                <reliability>
                    <kind>RELIABLE_RELIABILITY_QOS</kind>
                    <max_blocking_time>
                        <sec>10</sec>
                        <nanosec>0</nanosec>
                    </max_blocking_time>
                </reliability>
                
                <history>
                    <kind>KEEP_ALL_HISTORY_QOS</kind>
                </history>
                
                <!-- These are typical protocol parameters for a reliable
                     DataWriter -->
                <protocol>
                    <rtps_reliable_writer>
                        <max_heartbeat_retries>
                            LENGTH_UNLIMITED
                        </max_heartbeat_retries>
                        <heartbeats_per_max_samples>
                            2
                        </heartbeats_per_max_samples>
                        <heartbeat_period>
                            <sec>0</sec>
                            <nanosec>100000000</nanosec> <!--100ms -->
                        </heartbeat_period>
                        <fast_heartbeat_period>
                            <sec>0</sec>
                            <nanosec>10000000</nanosec> <!--10ms -->
                        </fast_heartbeat_period>
                        <late_joiner_heartbeat_period>
                            <sec>0</sec>
                            <nanosec>10000000</nanosec> <!--10ms -->
                        </late_joiner_heartbeat_period>
                        <max_nack_response_delay>
                            <sec>0</sec>
                            <nanosec>0</nanosec>
                        </max_nack_response_delay>
                        <min_nack_response_delay>
                            <sec>0</sec>
                            <nanosec>0</nanosec>
                        </min_nack_response_delay>
                        <max_send_window_size>32</max_send_window_size>
                        <min_send_window_size>32</min_send_window_size>
                    </rtps_reliable_writer>
                </protocol>
                
                <writer_resource_limits>
                    <!-- This setting enables efficient communication
                         between a replier and an arbitrary number of requesters 
                     -->
                    <max_remote_reader_filters>
                        LENGTH_UNLIMITED
                    </max_remote_reader_filters>
                </writer_resource_limits>
            </datawriter_qos>
            
            <datareader_qos>
                <!-- Strict reliable -->
                <reliability>
                    <kind>RELIABLE_RELIABILITY_QOS</kind>
                    <max_blocking_time>
                        <sec>10</sec>
                        <nanosec>0</nanosec>
                    </max_blocking_time>
                </reliability>
                
                <history>
                    <kind>KEEP_ALL_HISTORY_QOS</kind>
                </history>
                
                <!-- These are typical protocol parameters for a reliable
                     DataReader -->
                <protocol>
                    <rtps_reliable_reader>
                        <max_heartbeat_response_delay>
                            <sec>0</sec>
                            <nanosec>0</nanosec>
                        </max_heartbeat_response_delay>
                        <min_heartbeat_response_delay>
                            <sec>0</sec>
                            <nanosec>0</nanosec>
                        </min_heartbeat_response_delay>
                    </rtps_reliable_reader>
                </protocol>
                
            </datareader_qos>
            
        </qos_profile>
    
        <!-- This is the profile used by the Requester. 
             It inherits from "default", defined above, 
             and overrides some QoS -->
        <qos_profile name="RequesterExampleProfile" 
                     base_name="default">

            <!-- QoS for the data writer that sends requests -->
            <datawriter_qos>
                <durability>
                    <kind>TRANSIENT_LOCAL_DURABILITY_QOS</kind>
                </durability>
            </datawriter_qos>

            <!-- QoS for the data reader that receives replies -->
            <datareader_qos>
                <durability>
                    <kind>VOLATILE_DURABILITY_QOS</kind>
                </durability>
            </datareader_qos>
        </qos_profile>

        <!-- This is the profile used by the Replier. 
             It inherits from "default", defined above, 
             and overrides some QoS -->
        <qos_profile name="ReplierExampleProfile"
                     base_name="default">
        
            <!-- QoS for the data writer that sends replies -->
            <datawriter_qos>
                <durability>
                    <kind>VOLATILE_DURABILITY_QOS</kind>
                </durability>
            </datawriter_qos>

            <!-- QoS for the data reader that receives requests -->
            <datareader_qos>
                <durability>
                    <kind>TRANSIENT_LOCAL_DURABILITY_QOS</kind>
                </durability>
            </datareader_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::Connext::RequestReply::Requester<TReq,TRep> using this profile.

See Also

Creating a Requester with optional parameters

Configuring QoS Profiles with XML