FASTRTPS(publisher-subscriber)实践及问题

Fast-RTPS 提供了两个层次的 API

	· publisher-Subscriber层：RTPS 上的简化抽象
	· Writer-Reader层，对于RTPS端点的直接控制(更底层）

Publisher-Subscriber层为大多数开发者提供了一个方便的抽象。允许定义与topic关联的发布者和订阅者，以及传输topic数据的简单方法。
Writer-Reader层更接近于RTPS标准中定义的概念，并且可以进行更精准的控制，但是要求开发者直接与每个端点的历史记录缓存进行交互。

这篇文章是基于 Publisher-Subscriber层 进行记录的，如果文中的问题有道友知道解决方法，劳烦指出，谢谢。

首先安装就不说了，包括 fastrtpsgen 的安装，现在这个工具叫 fastddsgen，是一样的。看别的博客，也有人自己改用的 protobuf 做序列化，这个我还没研究，不太清除。

先编写好 msg.idl 文件，里面是定义的通讯格式，比如一个结构体，如下

struct MSG
{
    unsigned long index;
    string rbuf;
};

然后使用 fastddsgen 工具，使用命令fastddsgen msg.idl
就会生成四个文件 xxx.cxx、 xxx.h、xxxPubSubTypes.cxx、 xxxPubSubTypes.h
如果需要例程文件，也可以使用命令 fastrtpsgen -example CMake msg.idl
就会生成几个 .cxx .h 文件，不过这里的 publihser.cpp subscriber.cpp我是自己写的

然后再找个例程，把cmakelists.txt 拷贝一下，然后修改一下
我这里简单贴一下，省得找

# Copyright 2016 Proyectos y Sistemas de Mantenimiento SL (eProsima).
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

cmake_minimum_required(VERSION 2.8.12)

if(NOT CMAKE_VERSION VERSION_LESS 3.0)
    cmake_policy(SET CMP0048 NEW)
endif()

project("DDSTCP")

# Find requirements
if(NOT fastcdr_FOUND)
    find_package(fastcdr REQUIRED)
endif()

if(NOT foonathan_memory_FOUND)
    find_package(foonathan_memory REQUIRED)
endif()

if(NOT fastrtps_FOUND)
    find_package(fastrtps REQUIRED)
endif()

#Check C++11
include(CheckCXXCompilerFlag)
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_CLANG OR
        CMAKE_CXX_COMPILER_ID MATCHES "Clang")
    check_cxx_compiler_flag(-std=c++11 SUPPORTS_CXX11)
    if(NOT SUPPORTS_CXX11)
        message(FATAL_ERROR "Compiler doesn't support C++11")
    endif()
endif()

message(STATUS "Configuring DDSTCP example...")
file(GLOB HELLOWORLD_EXAMPLE_SOURCES_CXX "*.cxx")
file(GLOB HELLOWORLD_EXAMPLE_SOURCES_CPP "*.cpp")
#file(GLOB XML_CONFIG_FILES "*.xml")
#message(STATUS "XML Files: " ${XML_CONFIG_FILES})
# configure_file("HelloWorldSubscriber.xml" "HelloWorldSubscriber.xml" COPYONLY)
# configure_file("HelloWorldPublisher.xml" "HelloWorldPublisher.xml" COPYONLY)
# configure_file("dh2048.pem" "dh2048.pem" COPYONLY)
# configure_file("server.pem" "server.pem" COPYONLY)
# configure_file("ca.pem" "ca.pem" COPYONLY)


add_executable(ddstcp ${HELLOWORLD_EXAMPLE_SOURCES_CXX} ${HELLOWORLD_EXAMPLE_SOURCES_CPP})
target_compile_definitions(ddstcp PRIVATE
    $<$<AND:$<NOT:$<BOOL:${WIN32}>>,$<STREQUAL:"${CMAKE_BUILD_TYPE}","Debug">>:__DEBUG>
    $<$<BOOL:${INTERNAL_DEBUG}>:__INTERNALDEBUG> # Internal debug activated.
)
target_link_libraries(ddstcp fastrtps fastcdr foonathan_memory fastdds::optionparser)
#install(TARGETS ddstcp
#    RUNTIME DESTINATION examples/C++/ddstcp/${BIN_INSTALL_DIR})

现在说一下publisher里面

/**
 * @file msgPublisher.h
 *
 */
#ifndef MSGPUBLISHER_H_
#define MSGPUBLISHER_H_

#include 
#include 
#include 

#include "messagePubSubTypes.h"
#include "message.h"
#include 

class MsgPublisher
{
    class PubListener : public eprosima::fastrtps::PublisherListener
    {
    public:
        PubListener() : n_matched(0), firstConnected(false){};

        ~PubListener(){};

        // 回调实现。每当发布者在网络上找到侦听同一主题的订阅者时，就会调用此函数
        void onPublicationMatched(eprosima::fastrtps::Publisher *pub, eprosima::fastrtps::rtps::MatchingInfo &info);
        // 回调函数，错过截止日期时调用的方法
        void on_offered_deadline_missed(eprosima::fastrtps::Publisher *pub, const eprosima::fastrtps::OfferedDeadlineMissedStatus &status);
        // 回调函数，当发布者的活力丧失时调用的方法
        void on_liveliness_lost(eprosima::fastrtps::Publisher *pub, const eprosima::fastrtps::LivelinessLostStatus &status);

        int n_matched;
        bool firstConnected;
    } listener_;

    DDSTCP message_;
    eprosima::fastrtps::Participant *participant_;
    eprosima::fastrtps::Publisher *publisher_;
    DDSTCPPubSubType type_;

    void runThread(uint32_t number, long sleep_ms);

public:
    MsgPublisher();

    virtual ~MsgPublisher();

    //! Initialize
    bool init(const std::string &wan_ip, unsigned short port, std::string topicDataType, std::string topicName);

    // fill publisher buff
    bool getPublishMsg(char *p);

    //! Publish a sample
    bool publish(bool waitForListener = true);

    //! Run for number samples
    void run(uint32_t number, long sleep_ms);
};

#endif /* MSGPUBLISHER_H_ */

这里面的三个回调函数，都是基于父类里面找出来的，就只有 onPublicationMatched 这个函数，在找到订阅者的时候会调用一下，然后订阅者丢失，不会再次调用，就是这个坑。其他两个函数基本不会调用。

所以就会导致问题，n_matched 匹配的个数只会增长，不会下降。

void MsgPublisher::PubListener::onPublicationMatched(Publisher *, MatchingInfo &info)
{
    printf("发现回调函数........\n ");
    if (info.status == MATCHED_MATCHING)
    {
        n_matched++;
        firstConnected = true;
        // logError(HW, "Matched");
        std::cout << "Publisher matched, online num = " << n_matched << std::endl;
    }
    else
    {
        n_matched--;
        std::cout << "Publisher unmatched, online num = " << n_matched << std::endl;
    }
}

就这样，记录完毕，下次记录 reader-writer层