实现数据库连接池

文章目录

1. 1. 单例模式创建连接池
2. 2. 初始化
3. 3. 获取&释放连接
4. 4. 销毁连接池
5. 5. RAII 释放数据库连接
6. 6. 参考资料

数据库连接池采用单例模式创建，使用 RAII 机制释放数据库连接。

单例模式创建连接池

class connection_pool
{
public:
     //局部静态变量单例模式
    static connection_pool *GetInstance();

private:
    connection_pool();
    ~connection_pool();
}

connection_pool *connection_pool::GetInstance()
{
    static connection_pool connPool;
    return &connPool;
}

初始化

connection_pool::connection_pool()
{
	m_CurConn = 0;
	m_FreeConn = 0;
}

//构造初始化
void connection_pool::init(string url, string User, string PassWord, string DBName, int Port, int MaxConn, int close_log)
{
	m_url = url;
	m_Port = Port;
	m_User = User;
	m_PassWord = PassWord;
	m_DatabaseName = DBName;
	m_close_log = close_log;

	for (int i = 0; i < MaxConn; i++)
	{
		MYSQL *con = NULL;
		con = mysql_init(con);

		if (con == NULL)
		{
			LOG_ERROR("MySQL Error");
			exit(1);
		}
		con = mysql_real_connect(con, url.c_str(), User.c_str(), PassWord.c_str(), DBName.c_str(), Port, NULL, 0);

		if (con == NULL)
		{
			LOG_ERROR("MySQL Error");
			exit(1);
		}
		connList.push_back(con);
		++m_FreeConn;
	}

	reserve = sem(m_FreeConn);

	m_MaxConn = m_FreeConn;
}

获取&释放连接

//当有请求时，从数据库连接池中返回一个可用连接，更新使用和空闲连接数
MYSQL *connection_pool::GetConnection()
{
	MYSQL *con = NULL;

	if (0 == connList.size())
		return NULL;

	reserve.wait();  // 取出连接，信号量原子 -1， 为0则等待
	
	lock.lock();

	con = connList.front();
	connList.pop_front();

	--m_FreeConn;
	++m_CurConn;

	lock.unlock();
	return con;
}

//释放当前使用的连接
bool connection_pool::ReleaseConnection(MYSQL *con)
{
	if (NULL == con)
		return false;

	lock.lock();

	connList.push_back(con);
	++m_FreeConn;
	--m_CurConn;

	lock.unlock();

	reserve.post();  // 释放连接 原子+1
	return true;
}

销毁连接池

//销毁数据库连接池
void connection_pool::DestroyPool()
{

	lock.lock();
	if (connList.size() > 0)
	{
		list<MYSQL *>::iterator it;
		for (it = connList.begin(); it != connList.end(); ++it)
		{
			MYSQL *con = *it;
			mysql_close(con);
		}
		m_CurConn = 0;
		m_FreeConn = 0;
		connList.clear();
	}

	lock.unlock();
}

RAII 释放数据库连接

class connectionRAII{

public:
    //双指针对MYSQL *con修改
    connectionRAII(MYSQL **con, connection_pool *connPool);
    ~connectionRAII();

private:
    MYSQL *conRAII;
    connection_pool *poolRAII;
};

不直接调用获取和释放连接的接口，将其封装起来，通过RAII机制进行获取和释放。

connectionRAII::connectionRAII(MYSQL **SQL, connection_pool *connPool){
	*SQL = connPool->GetConnection();
	
	conRAII = *SQL;
	poolRAII = connPool;
}

connectionRAII::~connectionRAII(){
	poolRAII->ReleaseConnection(conRAII);
}

参考资料

• sql_connection_pool
• 11 数据库连接池