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【已上线】C++ mysql连接池

article 2025/2/28 2:58:58

目录

  • 1 为什么需要链接池
  • 2 实现原理
  • 3 代码
  • 4 编译
  • 5 参考

1 为什么需要链接池

  1. 可以复用已经建立好的链接，节约数据库建立链接的时间。原理上，和线程池类似。
  2. 我们项目中的一个实际需求，同时可能有多个线程同时访问数据库。这样每个线程都需要和数据库建立链接才能保证线程安全。有了链接池，即可以复用已有的链接，有保证的线程安全。

2 实现原理

db_connection.h和 db_connection.cpp是对数据库链接的封装
db_connection_pool.h和db_connection_pool.cpp是链接池的实现。在初始化的时候，会提前构造一些链接放到容器中，当池子空了之后，采用生产者-消费者模式构造链接。如果构造的链接个数到达指定上限，从链接池里获取链接的时候，就会失败。另外，我们也会有一个单独的线程，删除长时间不用的链接，让链接池的大小保持在初始大小。

3 代码

// db_connection.h

#pragma once

#include <string>
#include <chrono>
#include "mysql/mysql.h"

class DBConnection {
public:
    DBConnection();
    ~DBConnection();
    bool connect(std::string host, int port, std::string user, std::string password, std::string dbname);
    bool update(std::string sql);
    MYSQL_RES* query(std::string sql);
    // 如果这个链接被使用了，就刷新一下时间。因为链接池会把好久不用的多于链接删除
    void refreshAliveTime() { m_alivetime = std::chrono::system_clock::now(); }
    int getAliveeTime() const { return std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now() - m_alivetime).count(); }

private:
    MYSQL* m_conn;
    std::chrono::system_clock::time_point m_alivetime;
};

// db_connection.cpp

#include "db_connection.h"

DBConnection::DBConnection() {
    m_conn = mysql_init(nullptr);
}

DBConnection::~DBConnection() {
    if (m_conn != nullptr)
        mysql_close(m_conn);
}

bool DBConnection::connect(std::string host, int port, std::string user, std::string password, std::string dbname) {
    if (mysql_real_connect(m_conn, host.c_str(), user.c_str(), password.c_str(), dbname.c_str(), port, nullptr, 0) == nullptr) {
        return false;
    }
    // mysql_query(m_conn, "set names utf8mb4");
    mysql_set_character_set(m_conn, "utf8");
    return true;
}

bool DBConnection::update(std::string sql) {
    if (mysql_query(m_conn, sql.c_str())) {
        return false;
    }
    return true;
}

MYSQL_RES* DBConnection::query(std::string sql) {
    if (mysql_query(m_conn, sql.c_str())) {
        return nullptr;
    }
    return mysql_use_result(m_conn);
}

// db_connection_pool.h

#pragma once

#include "db_connection.h"

#include <queue>
#include <mutex>
#include <thread>
#include <atomic>
#include <functional>
#include <condition_variable>

class DBConnectionPool {
public:
    static DBConnectionPool* getInstance();
    bool init(const std::string& config);
    std::shared_ptr<DBConnection> getConnection();

    std::string getTable() const { return m_table; }
    
private:
    DBConnectionPool() = default;
    bool loadConfigFile(const std::string& config);
    void produceConnectionTask();
    void scannerConnectionTask();
    bool createTable();

private:
    std::string m_host;         // 数据库ip
    int m_port;                 // 数据端口号
    std::string m_user;         // 用户名
    std::string m_password;     // 密码
    std::string m_database;     // 数据库名
    std::string m_table;        // 表名
    
    int m_initSize;              // 初始链接数
    int m_maxSize;               // 最大链接数
    int m_maxIdleTime;           // 单位: s
    int m_connectionTimeout;     // 单位: s
    
    std::queue<DBConnection*> m_connectionQueue;    // 存放链接的容器
    std::mutex m_connectionQueueMutex;              // 保证容器操作线程安全
    std::atomic_int m_connectionCnt;                // 容器大小
    std::condition_variable m_cv;                   // 用作线程通讯的信号
};

// db_connection_pool.cpp

#include "db_connection_pool.h"

#include <thread>

#include "rapidjson/document.h"             // 用来解析json
#include "rapidjson/filereadstream.h"
#include "rapidjson/error/en.h"

namespace handler_process {

DBConnectionPool* DBConnectionPool::getInstance() {
    static DBConnectionPool pool;
    return &pool;
}

bool DBConnectionPool::init(const std::string& config) {
    if (!loadConfigFile(config)) {
        ASYNC_LOG_ERROR("[DBConnectionPool::init] loadConfigFile failure");
        return false;
    }

    ASYNC_LOG_INFO("[DBConnectionPool::init] init success, create db connection pool, size: {}", m_initSize);
    m_connectionCnt = 0;
    for (int i = 0; i < m_initSize; ++i) {
        DBConnection* conn = new DBConnection();
        if (!conn->connect(m_host, m_port, m_user, m_password, m_database)) {
            ASYNC_LOG_ERROR("[DBConnectionPool::init] connect failure, host: {}, port: {}, user: {}, dbname: {}", m_host, m_port, m_user, m_database);
            delete conn;
            continue;
        }

        conn->refreshAliveTime();
        m_connectionQueue.push(conn);
        m_connectionCnt++;
    }

    if (m_connectionCnt.load() == 0) {
        ASYNC_LOG_ERROR("[DBConnectionPool::init] init failure, create db connection pool failure");
        return false;
    }
    ASYNC_LOG_INFO("[DBConnectionPool::init] init success, create db connection pool succ, size: {}", m_connectionCnt.load());

	// 如果池子空了，这个线程负责构造新的链接
    std::thread produce(std::bind(&DBConnectionPool::produceConnectionTask, this));
    produce.detach();

	// 这个线程负责删除多于的链接
    std::thread scanner(std::bind(&DBConnectionPool::scannerConnectionTask, this));
    scanner.detach();

    if (!createTable()) {
        ASYNC_LOG_ERROR("[DBConnectionPool::init] create table failure");
        return false;
    }

    return true;
}

bool DBConnectionPool::loadConfigFile(const std::string& config) {
    ASYNC_LOG_INFO("[DBConnectionPool::loadConfigFile] config_file: {}", config);
    
    FILE* fp = fopen(config.c_str(), "r");
    if (!fp) {
        ASYNC_LOG_ERROR("[DBConnectionPool::loadConfigFile] unable to open file: {}", config);
        return false;
    }

    // 创建文件读取流
    char readBuffer[65536];
    rapidjson::FileReadStream is(fp, readBuffer, sizeof(readBuffer));

    // 解析JSON数据
    rapidjson::Document document;
    if (document.ParseStream(is).HasParseError()) {
        ASYNC_LOG_ERROR("[DBConnectionPool::loadConfigFile] parse error");
        fclose(fp);
        return false;
    }
    fclose(fp);
    
	m_table = std::string(document["table"].GetString());
	m_host = std::string(document["host"].GetString());
	m_user = std::string(document["user"].GetString());
	m_password = std::string(document["password"].GetString());
	m_database = std::string(document["database"].GetString());
	m_port = document["port"].GetInt();

    m_initSize = document["connection_pool_init_size"].GetInt();
    m_maxSize = document["connection_pool_max_size"].GetInt();
    m_maxIdleTime = document["connection_pool_max_idle_time"].GetInt();
    m_connectionTimeout = document["connection_pool_max_wait_time"].GetInt();

    ASYNC_LOG_INFO("[DBConnectionPool::loadConfigFile] m_manualInterventionInfoTableName: {}, m_dynamicDBInfoTableName: {}, " \
            "m_host: {}, m_user: {}, m_database: {}, m_port: {}, m_initSize: {}, m_maxSize: {}, m_maxIdleTime: {}, m_connectionTimeout: {}",
            m_manualInterventionInfoTableName, m_dynamicDBInfoTableName,
            m_host, m_user, m_database, m_port, m_initSize, m_maxSize, m_maxIdleTime, m_connectionTimeout);

    return true;
}

bool DBConnectionPool::createTable() {
    std::shared_ptr<DBConnection> dbConnection = getConnection();
    if (!dbConnection) {
        ASYNC_LOG_ERROR("[DBConnectionPool::createTable] get connection failure");
        return false;
    }

    std::string create_table_query_1 = "CREATE TABLE IF NOT EXISTS " + m_table + 
        "(id INT AUTO_INCREMENT PRIMARY KEY)";

    return dbConnection->update(create_table_query_1);
}

void DBConnectionPool::produceConnectionTask() {
    while (true) {
        std::unique_lock<std::mutex> lock(m_connectionQueueMutex);
        while (!m_connectionQueue.empty()) {
            m_cv.wait(lock);
        }

        if (m_connectionCnt.load() < m_maxSize) {
            DBConnection* conn = new DBConnection();
            if (!conn->connect(m_host, m_port, m_user, m_password, m_database)) {
                ASYNC_LOG_ERROR("[DBConnectionPool::produceConnectionTask] connect failure, host: {}, port: {}, user: {}, dbname: {}", m_host, m_port, m_user, m_database);
                delete conn;

                std::this_thread::sleep_for(std::chrono::seconds(3));
                continue;
            }

            conn->refreshAliveTime();
            m_connectionQueue.push(conn);
            m_connectionCnt++;
            ASYNC_LOG_INFO("[DBConnectionPool::produceConnectionTask] produce connection succ, m_connectionCnt: {}", m_connectionCnt.load());
        }

        m_cv.notify_all();
    }
}

void DBConnectionPool::scannerConnectionTask() {
    while (true) {
        ASYNC_LOG_INFO("[DBConnectionPool::scannerConnectionTask] scanner connection, m_connectionCnt: {}, m_maxIdleTime: {}s", m_connectionCnt.load(), m_maxIdleTime);
        std::this_thread::sleep_for(std::chrono::seconds(m_maxIdleTime));

        std::unique_lock<std::mutex> lock(m_connectionQueueMutex);
        while (m_connectionCnt.load() > m_initSize) {
            DBConnection* conn = m_connectionQueue.front();
            if (conn->getAliveeTime() >= m_maxIdleTime) {
                m_connectionQueue.pop();
                m_connectionCnt--;
                delete conn;
            } else {
                break;  // 队头的连接没有超过m_maxIdleTime，其它连接肯定没有
            }
        }
    }
}

std::shared_ptr<DBConnection> DBConnectionPool::getConnection() {
    std::unique_lock<std::mutex> lock(m_connectionQueueMutex);
    while (m_connectionQueue.empty()) {
        if (m_cv.wait_for(lock, std::chrono::seconds(m_connectionTimeout)) == std::cv_status::timeout) {
            if (m_connectionQueue.empty()) {
                ASYNC_LOG_ERROR("[DBConnectionPool::getConnection] get connection timeout: {}", m_connectionTimeout);
                return nullptr;
            }
        }
    }
    
    std::shared_ptr<DBConnection> conn(m_connectionQueue.front(), [&](DBConnection* pconn) {
        std::unique_lock<std::mutex> lock(m_connectionQueueMutex);
        pconn->refreshAliveTime();
        m_connectionQueue.push(pconn);
        m_connectionCnt++;
    });

    m_connectionQueue.pop();
    m_connectionCnt--;
    m_cv.notify_all();
    ASYNC_LOG_INFO("[DBConnectionPool::getConnection] get connection success, residue m_connectionCnt: {}", m_connectionCnt.load());
    return conn;
}

配置文件：

// db_conf.json
{
    "table": "test_table",
    "host": "10.10.10.123",
    "user": "root",
    "password": "123456",
    "database": "test_db",
    "port": 3306,
    "connection_pool_init_size": 5,
    "connection_pool_max_size" : 50,
    "connection_pool_max_idle_time": 600,
    "connection_pool_max_wait_time": 5
}

使用方式：

// main.cpp

#include <iostream>
#include "db_connection_pool.h"

int main(int argc, char** argv) {
	if (!handler_process::DBConnectionPool::getInstance()->init("db_conf.json")) {
		std::cerr << "init db connection pool failure" << std::endl;
		return -1;
	}

	std::shared_ptr<DBConnection> dbConnection = DBConnectionPool::getInstance()->getConnection();
	std::string  querySql = "SELECT * FROM " + DBConnectionPool::getInstance()->getTable() + " WHERE id = 1"; 
	MYSQL_RES* res = dbConnection->query(querySql);
    if (res == nullptr) {
    	std::cerr << "query err" << std::endl;
        return -1;
    }

	MYSQL_ROW column;
	while((column = mysql_fetch_row(res)) != NULL) {
		try {
			int id = std::stoi(column[0]);
		} catch (const std::exception& e) {
			std::cerr << "exception: " << e.what() << std::endl;
			continue;
		}
	}
	mysql_free_result(res);
	return 0;
}

4 编译

如果是centos，使用yum安装mysql客户端

yum install -y mysql-devel mysql

CMakeLists.txt

...
link_directories("/usr/lib64/mysql")
set(MYSQL_LIBS mysqlclient)
add_executable(main main.cpp db_connection.cpp db_connection_pool.cpp)
target_link_libraries(main pthread ${MYSQL_LIBS})

5 参考

C++ mysql连接池 附带讲解与详细注释源码


http://www.kler.cn/a/280937.html

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