FastDDS 源码解析（二十三）创建User的DataReader（上）

sequenceDiagram participant Application participant DomainParticipantFactory participant DomainParticipant participant DomainParticipantImpl participant TypeSupport participant Subscriber Application ->> DomainParticipantFactory:1.get_instance DomainParticipantFactory ->> DomainParticipantFactory: 2.create_participant DomainParticipantFactory ->> DomainParticipant: 3.new DomainParticipant DomainParticipantFactory ->> DomainParticipantImpl: 4.new DomainParticipantImpl DomainParticipantImpl ->> DomainParticipantFactory: return DomainParticipantImpl DomainParticipantFactory ->> DomainParticipant: 5.enable Application ->> TypeSupport:6.register_type Application ->> DomainParticipantImpl: 7.create_subscriber Application ->> DomainParticipantImpl: 8.create_topic Application ->> Subscriber: 9.create_dataReader

DomainParticipantFactory::get_instance() 获取一个DomainParticipantFactory的对象
DomainParticipantFactory 调用create_participant主要干了三件事情：

a.new DomainParticipant() 见步骤3

b.new DomainParticipantImpl() 在这里DomainParticipant 和DomainParticipantImpl对象是一一对应关系见步骤4

c.调用DomainParticipant对象的enable函数，最终会调用到 DomainParticipantImpl对象的enable函数，就是启动participant 见步骤5
new 了一个DomainParticipant
new了一个 DomainParticipantImpl()
调用DomainParticipant对象的enable函数
注册type，这个type 和 topic 是关联关系
只有同一个topic的2个participant 才能互相通信，通信内容的解析需要使用type解析
调用DomainParticipantImpl的create_subscriber函数，配置qos
调用DomainParticipantImpl的create_topic函数，配置qos
调用Publihser的create_datawriter函数，配置qos，发送消息就是由这个datawriter执行的

1.2源码

不再展开

参考第一篇车载消息中间件FastDDS 源码解析（一）FastDDS 介绍和使用接收端代码示例部分

2.创建Subscriber

sequenceDiagram participant User participant DomainParticipant participant DomainParticipantImpl participant Subscriber participant SubscriberImpl User ->> DomainParticipant: 1.create_subscriber DomainParticipant ->> DomainParticipantImpl: 2.create_subscriber DomainParticipantImpl ->> DomainParticipantImpl: 3.create_subscriber_impl DomainParticipantImpl ->> SubscriberImpl: 4.new DomainParticipantImpl ->> Subscriber: 5.new DomainParticipantImpl ->> Subscriber: 6.enable Subscriber ->> SubscriberImpl: 7.enable

1.用户程序调用DomainParticipant的create_subscriber函数，这个函数调用的是DomainParticipantImpl的create_subscriber函数

2.DomainParticipantImpl的create_subscriber函数主要干了4件事

a.创建SubscriberImpl对象见3

b.在SubscriberImpl对象的基础上创建Subscriber 见4

c.给SubscriberImpl对象分配instance_handle（guid）见5

d.调用Subscriber对象的enable函数见6

3.create_subscriber_impl 创建SubscriberImpl对象

4.创建SubscriberImpl对象

5.在SubscriberImpl的基础上创建Subscriber

6.调用Subscriber的enable函数

7.调用SubscriberImpl对象的enable函数

步骤1:

rust 复制代码

 Subscriber* DomainParticipant::create_subscriber(
         const SubscriberQos& qos,
         SubscriberListener* listener,
         const StatusMask& mask)
     return impl_->create_subscriber(qos, listener, mask);
 }

调用DomainParticipantImpl的create_subscriber

步骤2:

perl 复制代码

 Subscriber* DomainParticipantImpl::create_subscriber(
         const SubscriberQos& qos,
         SubscriberListener* listener,
         const StatusMask& mask)
 {
     if (!SubscriberImpl::check_qos(qos))
     {
         // The SubscriberImpl::check_qos() function is not yet implemented and always returns ReturnCode_t::RETCODE_OK.
         // It will be implemented in future releases of Fast DDS.
         // EPROSIMA_LOG_ERROR(PARTICIPANT, "SubscriberQos inconsistent or not supported");
         // return nullptr;
     }
 
     //TODO CONSTRUIR LA IMPLEMENTACION DENTRO DEL OBJETO DEL USUARIO.
     SubscriberImpl* subimpl = create_subscriber_impl(qos, listener);
     Subscriber* sub = new Subscriber(subimpl, mask);
     subimpl->user_subscriber_ = sub;
     subimpl->rtps_participant_ = get_rtps_participant();
 
     // Create InstanceHandle for the new subscriber
     InstanceHandle_t sub_handle;
     bool enabled = get_rtps_participant() != nullptr;
 
     // Create InstanceHandle for the new subscriber
     create_instance_handle(sub_handle);
     subimpl->handle_ = sub_handle;
 
     //SAVE THE PUBLISHER INTO MAPS
     std::lock_guard<std::mutex> lock(mtx_subs_);
     subscribers_by_handle_[sub_handle] = sub;
     subscribers_[sub] = subimpl;
 
     // Enable subscriber if appropriate
     if (enabled && qos_.entity_factory().autoenable_created_entities)
     {
         ReturnCode_t ret_subscriber_enable = sub->enable();
         assert(ReturnCode_t::RETCODE_OK == ret_subscriber_enable);
         (void)ret_subscriber_enable;
     }
 
     return sub;
 }

主要干了4件事

1.创建SubscriberImpl对象见步骤3

2.在SubscriberImpl对象的基础上创建Subscriber 见步骤4

3.给SubscriberImpl对象分配instance_handle（guid）见步骤5

4.调用Subscriber对象的enable函数见步骤6

步骤3:

javascript 复制代码

 SubscriberImpl* DomainParticipantImpl::create_subscriber_impl(
         const SubscriberQos& qos,
         SubscriberListener* listener)
 {
     return new SubscriberImpl(this, qos, listener);
 }

步骤4-5没啥关键信息

步骤6:

ini 复制代码

 ReturnCode_t Subscriber::enable()
 {
     if (enable_)
     {
         return ReturnCode_t::RETCODE_OK;
     }
 
     if (false == impl_->get_participant()->is_enabled())
     {
         return ReturnCode_t::RETCODE_PRECONDITION_NOT_MET;
     }
 
     enable_ = true;
     ReturnCode_t ret_code = impl_->enable();
     enable_ = ReturnCode_t::RETCODE_OK == ret_code;
     return ret_code;
 }

主要是调用了SubscriberImpl的enable函数见步骤7:

步骤7:

css 复制代码

 ReturnCode_t SubscriberImpl::enable()
 {
     if (qos_.entity_factory().autoenable_created_entities)
     {
         std::lock_guard<std::mutex> lock(mtx_readers_);
         for (auto topic_readers : readers_)
         {
             for (DataReaderImpl* dr : topic_readers.second)
             {
                 dr->user_datareader_->enable();
             }
         }
     }
 
     return ReturnCode_t::RETCODE_OK;
 }

调用SubscriberImpl中的DataReaderImpl的DataReader的enable函数

3.创建DataReader

sequenceDiagram participant User participant Subscriber participant SubscriberImpl participant DataReaderImpl participant DataReader participant RTPSDomainImpl participant RTPSParticipantImpl User ->> Subscriber:1.create_datareader Subscriber ->> SubscriberImpl:2.create_datareader SubscriberImpl ->> SubscriberImpl:3.create_datareader_impl SubscriberImpl ->> DataReaderImpl:4.new SubscriberImpl ->> DataReader:5.new SubscriberImpl ->> DataReader:6.enable DataReader ->> DataReaderImpl:7.enable DataReaderImpl ->> RTPSDomainImpl:8.create_rtps_reader RTPSDomainImpl ->> RTPSParticipantImpl:9.create_reader DataReaderImpl ->> RTPSParticipantImpl:10.registerReader

可以参考FastDDS 源码解析（二十一）创建User的DataWriter（上）创建DataWriter，这里介绍的是创建DataReader，基本是类似的。

1.Subscriber的create_datareader函数调用的是SubscriberImpl的create_datareader函数

2.SubscriberImpl的create_datareader函数最终干了3件事

a.获取TypeSupport

b.调用create_datareader_impl函数来创建DataReaderImpl对象，传入参数TypeSupport对象见步骤3

c.调用create_datareader创建 DataReader对象，传入参数DataReaderImpl对象见步骤 5

d.调用DataReader的enable函数见步骤6

3.SubscriberImpl的create_datareader_impl函数，调用了DataReaderImpl的初始化函数创建了一个DataReaderImpl的对象

4.new 了一个DataReaderImpl对象

5.new 了一个DataReader对象

6.DataReader对象的enable函数调用的是DataReaderImpl对象的enable函数

7.DataReaderImpl对象的enable函数主要干了2件事

a.调用RTPSDomainImpl的create_rtps_reader函数见 8

b.调用RTPSParticipantImpl的registerReader函数见 10

8.RTPSDomainImpl的create_rtps_reader函数主要是调用了RTPSParticipantImpl的create_reader函数

9.RTPSParticipantImpl的create_reader函数主要是创建了RTPSReader

10.RTPSParticipantImpl的registerReader函数主要是将reader的信息，存入PDP信息中，同时和writer进行匹配

步骤1:

javascript 复制代码

 DataReader* Subscriber::create_datareader(
         TopicDescription* topic,
         const DataReaderQos& reader_qos,
         DataReaderListener* listener,
         const StatusMask& mask)
 {
     return impl_->create_datareader(topic, reader_qos, listener, mask);
 }

调用的是SubscriberImpl的create_datareader函数

步骤2:

rust 复制代码

 DataReader* SubscriberImpl::create_datareader(
         TopicDescription* topic,
         const DataReaderQos& qos,
         DataReaderListener* listener,
         const StatusMask& mask)
 {
     EPROSIMA_LOG_INFO(SUBSCRIBER, "CREATING SUBSCRIBER IN TOPIC: " << topic->get_name());
     //Look for the correct type registration
     TypeSupport type_support = participant_->find_type(topic->get_type_name());
 
     /// Preconditions
     // Check the type was registered.
     if (type_support.empty())
     {
         EPROSIMA_LOG_ERROR(SUBSCRIBER, "Type : " << topic->get_type_name() << " Not Registered");
         return nullptr;
     }
 
     if (!DataReaderImpl::check_qos_including_resource_limits(qos, type_support))
     {
         return nullptr;
     }
 
     topic->get_impl()->reference();
 
     DataReaderImpl* impl = create_datareader_impl(type_support, topic, qos, listener);
     DataReader* reader = new DataReader(impl, mask);
     impl->user_datareader_ = reader;
 
     {
         std::lock_guard<std::mutex> lock(mtx_readers_);
         readers_[topic->get_name()].push_back(impl);
     }
 
     if (user_subscriber_->is_enabled() && qos_.entity_factory().autoenable_created_entities)
     {
         if (ReturnCode_t::RETCODE_OK != reader->enable())
         {
             delete_datareader(reader);
             return nullptr;
         }
     }
 
     return reader;
 }

主要干了3件事

1.获取TypeSupport

2.调用create_datareader_impl函数来创建DataReaderImpl对象，传入参数TypeSupport对象见步骤3

3.new了一个DataReader对象，传入参数DataReaderImpl对象

4.DataReader对象的enable函数见步骤6

步骤3:

typescript 复制代码

 DataReaderImpl* SubscriberImpl::create_datareader_impl(
         const TypeSupport& type,
         TopicDescription* topic,
         const DataReaderQos& qos,
         DataReaderListener* listener)
 {
     return new DataReaderImpl(this, type, topic, qos, listener);
 }

步骤4 new DataReaderImpl 没什么关键代码

步骤5 new DataReader 没什么关键代码

步骤6

ini 复制代码

 ReturnCode_t DataReader::enable()
 {
     if (enable_)
     {
         return ReturnCode_t::RETCODE_OK;
     }
 
     if (false == impl_->get_subscriber()->is_enabled())
     {
         return ReturnCode_t::RETCODE_PRECONDITION_NOT_MET;
     }
 
     ReturnCode_t ret_code = impl_->enable();
     enable_ = ReturnCode_t::RETCODE_OK == ret_code;
     return ret_code;
 }

主要调用了DataReaderImpl的enable函数

步骤7

ini 复制代码

 ReturnCode_t DataReaderImpl::enable()
 {
     assert(reader_ == nullptr);
 
     ReaderAttributes att;
 
     att.endpoint.durabilityKind = qos_.durability().durabilityKind();
     att.endpoint.endpointKind = READER;
     att.endpoint.reliabilityKind = qos_.reliability().kind == RELIABLE_RELIABILITY_QOS ? RELIABLE : BEST_EFFORT;
     att.endpoint.topicKind = type_->m_isGetKeyDefined ? WITH_KEY : NO_KEY;
     att.endpoint.multicastLocatorList = qos_.endpoint().multicast_locator_list;
     att.endpoint.unicastLocatorList = qos_.endpoint().unicast_locator_list;
     att.endpoint.remoteLocatorList = qos_.endpoint().remote_locator_list;
     att.endpoint.external_unicast_locators = qos_.endpoint().external_unicast_locators;
     att.endpoint.ignore_non_matching_locators = qos_.endpoint().ignore_non_matching_locators;
     att.endpoint.properties = qos_.properties();
     att.endpoint.ownershipKind = qos_.ownership().kind;
     att.endpoint.setEntityID(qos_.endpoint().entity_id);
     att.endpoint.setUserDefinedID(qos_.endpoint().user_defined_id);
     att.times = qos_.reliable_reader_qos().times;
     att.liveliness_lease_duration = qos_.liveliness().lease_duration;
     att.liveliness_kind_ = qos_.liveliness().kind;
     att.matched_writers_allocation = qos_.reader_resource_limits().matched_publisher_allocation;
     att.expectsInlineQos = qos_.expects_inline_qos();
     att.disable_positive_acks = qos_.reliable_reader_qos().disable_positive_ACKs.enabled;
 
 
     // TODO(Ricardo) Remove in future
     // Insert topic_name and partitions
     Property property;
     property.name("topic_name");
     property.value(topic_->get_impl()->get_rtps_topic_name().c_str());
     att.endpoint.properties.properties().push_back(std::move(property));
 
     std::string* endpoint_partitions = PropertyPolicyHelper::find_property(qos_.properties(), "partitions");
 
     if (endpoint_partitions)
     {
         property.name("partitions");
         property.value(*endpoint_partitions);
         att.endpoint.properties.properties().push_back(std::move(property));
     }
     else if (subscriber_->get_qos().partition().names().size() > 0)
     {
         property.name("partitions");
         std::string partitions;
         bool is_first_partition = true;
         for (auto partition : subscriber_->get_qos().partition().names())
         {
             partitions += (is_first_partition ? "" : ";") + partition;
             is_first_partition = false;
         }
         property.value(std::move(partitions));
         att.endpoint.properties.properties().push_back(std::move(property));
     }
 
     bool is_datasharing_compatible = false;
     ReturnCode_t ret_code = check_datasharing_compatible(att, is_datasharing_compatible);
     if (ret_code != ReturnCode_t::RETCODE_OK)
     {
         return ret_code;
     }
     if (is_datasharing_compatible)
     {
         DataSharingQosPolicy datasharing(qos_.data_sharing());
         if (datasharing.domain_ids().empty())
         {
             datasharing.add_domain_id(utils::default_domain_id());
         }
         att.endpoint.set_data_sharing_configuration(datasharing);
     }
     else
     {
         DataSharingQosPolicy datasharing;
         datasharing.off();
         att.endpoint.set_data_sharing_configuration(datasharing);
     }
 
     std::shared_ptr<IPayloadPool> pool = get_payload_pool();
     RTPSReader* reader = RTPSDomain::createRTPSReader(
         subscriber_->rtps_participant(),
         guid_.entityId,
         att, pool,
         static_cast<ReaderHistory*>(&history_),
         static_cast<ReaderListener*>(&reader_listener_));
 
     if (reader == nullptr)
     {
         release_payload_pool();
         EPROSIMA_LOG_ERROR(DATA_READER, "Problem creating associated Reader");
         return ReturnCode_t::RETCODE_ERROR;
     }
 
     auto content_topic = dynamic_cast<ContentFilteredTopicImpl*>(topic_->get_impl());
     if (nullptr != content_topic)
     {
         reader->set_content_filter(content_topic);
         content_topic->add_reader(this);
     }
 
     reader_ = reader;
 
     deadline_timer_ = new TimedEvent(subscriber_->get_participant()->get_resource_event(),
                     [&]() -> bool
                     {
                         return deadline_missed();
                     },
                     qos_.deadline().period.to_ns() * 1e-6);
 
     lifespan_timer_ = new TimedEvent(subscriber_->get_participant()->get_resource_event(),
                     [&]() -> bool
                     {
                         return lifespan_expired();
                     },
                     qos_.lifespan().duration.to_ns() * 1e-6);
 
     // Register the reader
     ReaderQos rqos = qos_.get_readerqos(subscriber_->get_qos());
     if (!is_datasharing_compatible)
     {
         rqos.data_sharing.off();
     }
     if (endpoint_partitions)
     {
         std::istringstream partition_string(*endpoint_partitions);
         std::string partition_name;
         rqos.m_partition.clear();
 
         while (std::getline(partition_string, partition_name, ';'))
         {
             rqos.m_partition.push_back(partition_name.c_str());
         }
     }
 
     rtps::ContentFilterProperty* filter_property = nullptr;
     if (nullptr != content_topic && !content_topic->filter_property.filter_expression.empty())
     {
         filter_property = &content_topic->filter_property;
     }
     if (!subscriber_->rtps_participant()->registerReader(reader_, topic_attributes(), rqos, filter_property))
     {
         EPROSIMA_LOG_ERROR(DATA_READER, "Could not register reader on discovery protocols");
 
         reader_->setListener(nullptr);
         stop();
 
         return ReturnCode_t::RETCODE_ERROR;
     }
 
     return ReturnCode_t::RETCODE_OK;
 }

主要干了这几件事情

1.调用RTPSDomainImpl::create_rtps_reader创建了一个RTPSReader，这是真正发送消息的对象见步骤8

RTPSReader的ReaderHistory和DataReaderImpl的DataReaderHistory是共用的，DataReaderHistory是ReaderHistory的子类

2.创建了2个TimedEvent

deadline_timer_

fastdds 有个qos 叫deadlineqos ，这个qos的参数一般是个周期性的时间，规定了在周期性的时间内，发送端必须发送一个消息出来。

在接收端在这个周期性的时间内需要收到一个消息。

lifespan_timer_

fastdds有个qos 叫lifespanqos，这个qos规定了，一个消息的存活时间，超过时间，会在发送端将消息移除，这个默认设置，会把存货时间设置为无限。

3.调用RTPSParticipant::registerReader，注册这个RTPSReader 见步骤10

步骤8:

rust 复制代码

 RTPSReader* RTPSDomain::createRTPSReader(
         RTPSParticipant* p,
         const EntityId_t& entity_id,
         ReaderAttributes& ratt,
         const std::shared_ptr<IPayloadPool>& payload_pool,
         ReaderHistory* rhist,
         ReaderListener* rlisten)
 {
     RTPSParticipantImpl* impl = p->mp_impl;
     if (impl)
     {
         RTPSReader* reader;
         if (impl->createReader(&reader, ratt, payload_pool, rhist, rlisten, entity_id))
         {
             return reader;
         }
     }
     return nullptr;
 }

调用RTPSParticipantImpl对象的create_reader，来创建RTPSReader对象，如果是reliable的RTPSReader，就是StatefulReader，如果是besteffort的RTPSReader，就是StatlessReader。

这个函数我们在之前介绍过，创建RTPSReader，创建ReceiverResources，将ReceiverResources的MessageReceiver 与RTPSReader关联，当MessageReceiver收到消息后，将会分配给相应的RTPSWriter或RTPSReader，让他们进行消息处理

步骤10:

这块内容，我们在下一篇介绍

总结：我们看到，创建DataReader的过程和之前创建DataWriter的过程基本是一致的，略有不同

2.3类图

classDiagram DomainParticipantImpl *-- SubscriberImpl DomainParticipantImpl *-- Subscriber Subscriber *-- SubscriberImpl SubscriberImpl *-- DataReaderImpl DataReaderImpl *-- RTPSReader class DomainParticipantImpl { +PublisherQos default_pub_qos_ +std::map publishers_ +SubscriberQos default_sub_qos_ +std::map subscribers_ } class SubscriberImpl { +std::map> readers_ } class Subscriber { +SubscriberImpl* mp_impl } class DataReaderImpl { +RTPSReader reader_ }

DomainParticipantImpl管理所有的Subscriber对象

Subscriber 和 SubscriberImpl 存储在一个map中（ std::map<Subscriber, SubscriberImpl> publishers_ ）
Subscriber 类似于 SubscriberImpl的代理类，Subscriber 和 SubscriberImpl 是一一对应的。
SubscriberImpl管理着DataReaderImpl对象。
DataReader 和 RTPSReader 是一一对应的。

这块代码我理解有些部分是有点冗余的，Subscriber 和 SubscriberImpl，DataReader和DataReaderImpl没必要分成2个类。