C++11 使用boost::signals2库信号槽机制实现责任链

这个其实就是使用C++传统的信号槽机制实现责任链。类似事件处理机制。其中connect函数所在的线程和程序原线程在不同的线程。信号槽机制也不改变原creature对象的值。它只是在信号槽的系统中记录一个当前值而已。在本例中creature对象的值被记录在Query对象的result字段中。
程序目录结构如下，

程序代码如下，
test/CMakeLists.txt

cmake_minimum_required(VERSION 2.6)

if(APPLE)
    message(STATUS "This is Apple, do nothing.")
    set(CMAKE_MACOSX_RPATH 1)
    set(CMAKE_PREFIX_PATH /Users/aabjfzhu/software/vcpkg/ports/cppwork/vcpkg_installed/x64-osx/share )
elseif(UNIX)
    message(STATUS "This is linux, set CMAKE_PREFIX_PATH.")
    set(CMAKE_PREFIX_PATH /vcpkg/ports/cppwork/vcpkg_installed/x64-linux/share)
endif(APPLE)

project(broken_chain)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-narrowing")

add_definitions(-g)

find_package(ZLIB)

find_package(OpenCV REQUIRED )
find_package(Arrow CONFIG REQUIRED)

find_package(unofficial-brotli REQUIRED)
find_package(unofficial-utf8proc CONFIG REQUIRED)
find_package(Thrift CONFIG REQUIRED)

find_package(glog REQUIRED)

find_package(OpenSSL REQUIRED)

find_package(Boost REQUIRED COMPONENTS
    system
    filesystem
    serialization
    program_options
    thread
    )

find_package(DataFrame REQUIRED)

if(APPLE)
    MESSAGE(STATUS "This is APPLE, set INCLUDE_DIRS")
set(INCLUDE_DIRS ${Boost_INCLUDE_DIRS} /usr/local/include /usr/local/iODBC/include /opt/snowflake/snowflakeodbc/include/ ${CMAKE_CURRENT_SOURCE_DIR}/../include/ ${CMAKE_CURRENT_SOURCE_DIR}/../../../include)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set INCLUDE_DIRS")
    set(INCLUDE_DIRS ${Boost_INCLUDE_DIRS} /usr/local/include ${CMAKE_CURRENT_SOURCE_DIR}/../include/   ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/)
endif(APPLE)


if(APPLE)
    MESSAGE(STATUS "This is APPLE, set LINK_DIRS")
    set(LINK_DIRS /usr/local/lib /usr/local/iODBC/lib /opt/snowflake/snowflakeodbc/lib/universal)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set LINK_DIRS")
    set(LINK_DIRS ${Boost_INCLUDE_DIRS} /usr/local/lib /vcpkg/ports/cppwork/vcpkg_installed/x64-linux/lib)
endif(APPLE)

if(APPLE)
    MESSAGE(STATUS "This is APPLE, set ODBC_LIBS")
    set(ODBC_LIBS iodbc iodbcinst)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set LINK_DIRS")
    set(ODBC_LIBS odbc odbcinst ltdl)
endif(APPLE)

include_directories(${INCLUDE_DIRS})
LINK_DIRECTORIES(${LINK_DIRS})

file( GLOB test_file_list ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp) 

file( GLOB APP_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/../impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../include/*.h ${CMAKE_CURRENT_SOURCE_DIR}/../include/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/arr_/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/http/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/yaml/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/df/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/death_handler/impl/*.cpp)

add_library(${PROJECT_NAME}_lib SHARED ${APP_SOURCES} ${test_file})
target_link_libraries(${PROJECT_NAME}_lib ${Boost_LIBRARIES} ZLIB::ZLIB glog::glog DataFrame::DataFrame ${OpenCV_LIBS})
target_link_libraries(${PROJECT_NAME}_lib OpenSSL::SSL OpenSSL::Crypto libgtest.a pystring libyaml-cpp.a libgmock.a ${ODBC_LIBS} libnanodbc.a pthread dl backtrace libzstd.a libbz2.a libsnappy.a re2::re2 parquet lz4 unofficial::brotli::brotlidec-static unofficial::brotli::brotlienc-static unofficial::brotli::brotlicommon-static utf8proc thrift::thrift  arrow arrow_dataset)

foreach( test_file ${test_file_list} )
    file(RELATIVE_PATH filename ${CMAKE_CURRENT_SOURCE_DIR} ${test_file})
    string(REPLACE ".cpp" "" file ${filename})
    add_executable(${file}  ${test_file})
    target_link_libraries(${file} ${PROJECT_NAME}_lib)
endforeach( test_file ${test_file_list})

test/broken_chain_test.cpp

#include "death_handler/death_handler.h"
#include 
#include "broken_chain.hpp"

#include "http/http_util.h"
#include 
#include 



int main(int argc, char** argv) {
    FLAGS_log_dir = "./";
    FLAGS_alsologtostderr = true;
    // 日志级别 INFO, WARNING, ERROR, FATAL 的值分别为0、1、2、3
    FLAGS_minloglevel = 0;

    Debug::DeathHandler dh;

    google::InitGoogleLogging("./logs.log");
    testing::InitGoogleTest(&argc, argv);
    int ret = RUN_ALL_TESTS();
    return ret;
}

GTEST_TEST(PointerChainTests, PointerChainAllChain) {

    Game game;
    Creature goblin {game, 1, 1,  "Goblin"};
    DoubleAttackModifier r1 {game, goblin};
    std::cout << goblin << "n"; 
    IncreaseDefenseModifier i1 {game, goblin};
    std::cout << goblin << "n";
    IncreaseDefenseModifier i2 {game, goblin};
    std::cout << goblin << "n";

    DoubleAttackModifier r2 {game, goblin};
    std::cout << goblin << "n";
    IncreaseDefenseModifier i3 {game, goblin};
    std::cout << goblin << "n"; 
} 

include/broken_chain.hpp

#ifndef _FREDRIC_BROKEN_CHAIN_HPP_
#define _FREDRIC_BROKEN_CHAIN_HPP_

#include 
#include 
#include 
#include 
#include 

struct Query {
    std::string creature_name;
    enum Argument {attack, defense} argument;
    int result;

    Query(std::string const& creature_name_, Argument argument_, int result_): argument{argument_}, result{result_}, creature_name{creature_name_}  {}
};

// mediator
struct Game {
    boost::signals2::signal queries;
};

struct Creature {
    Game& game;
    int attack, defense;
    std::string name;
public:
    Creature(Game& game_, int attack_, int defense_, std::string const& name_): game{game_}, attack{attack_}, defense{defense_}, name{name_} {}

    int get_attack() const {
        Query q {name, Query::Argument::attack, attack};
        game.queries(q);
        return q.result;
    }

    int get_defense() const {
        Query q {name, Query::Argument::defense, defense};
        game.queries(q);
        return q.result;
    }

    friend std::ostream& operator<<(std::ostream& os, Creature const& c) {
        os << "attack: " << c.get_attack() << " defense: " << c.get_defense() << " name: " << c.name;
        return os;
    }
};

class CreatureModifier {
protected:
    Game& game;
    Creature& creature;
public:
    CreatureModifier(Game& game_, Creature& creature_): game{game_}, creature{creature_} {

    }

    virtual ~CreatureModifier() = default;
};

class DoubleAttackModifier: public CreatureModifier {
    boost::signals2::connection conn;
public:
    DoubleAttackModifier(Game& game_, Creature& creature_): CreatureModifier(game_, creature_){
        conn = game.queries.connect([&](Query& q){
            if(q.creature_name == creature.name && q.argument == Query::Argument::attack) {
                q.result *= 2;
            }
        });
    }
};


class IncreaseDefenseModifier: public CreatureModifier {
    boost::signals2::connection conn;
    int attack{0};
public:
    IncreaseDefenseModifier(Game& game_, Creature& creature_): CreatureModifier(game_, creature_){
        attack = creature.get_attack();
        conn = game.queries.connect([&](Query& q){
            if(attack <= 2) {
                if(q.creature_name == creature.name && q.argument == Query::Argument::defense) {
                    q.result += 1; 
                }
            }
        });
    }
};

#endif

程序输出如下，