php代码实现mysql连接池效果

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循环从mysql连接池中获取连接，不需要重复创建新的连接。
参考配置修改：http://www.thinkphp.cn/topic/26541.html
防止访问量过大，把连接数占满了

<?php/** * @author xuleyan * @title mysql类 */class DbHelper{    //连接池    private $_pools = [];    //连接池大小    const POOLSIZE = 5;    const USERNAME = "root";    const PASSWORD = "root";    const HOST = "127.0.0.1";    const DB = "test";    public function __construct()        {        $db = self::DB;        $username = self::USERNAME;        $password = self::PASSWORD;        $host = self::HOST;        //持久化连接        $presistent = array(PDO::ATTR_PERSISTENT => true);        for ($i=0; $i < self::POOLSIZE; $i++) {             $connection = new PDO("mysql:dbname=$db;host=$host", $username, $password);            // sleep(3);            array_push($this->_pools, $connection);        }    }    //从数据库连接池中获取一个数据库链接资源    public function getConnection()    {        echo 'get' . count($this->_pools) . "<br>";        if (count($this->_pools) > 0) {            $one =  array_pop($this->_pools);            echo 'getAfter' . count($this->_pools) . "<br>";            return $one;        } else {            throw new ErrorException ( "<mark>数据库连接池中已无链接资源，请稍后重试!</mark>" );        }    }    //将用完的数据库链接资源放回到数据库连接池    public function release($conn)    {        echo 'release' . count($this->_pools) . "<br>";        if (count($this->_pools) >= self::POOLSIZE) {            throw new ErrorException ( "<mark>数据库连接池已满!</mark>" );        } else {            array_push($this->_pools, $conn);            // $conn = null;            echo 'releaseAfter' . count($this->_pools) . "<br>";        }    }    public function query($sql)    {        try {            $conn = $this->getConnection();            $res = $conn->query($sql);            $this->release($conn);            return $res;        } catch (ErrorException $e) {            print 'error:' . $e->getMessage();            die;        }    }    public function queryAll($sql)    {        try {            $conn = $this->getConnection();            $sth = $conn->prepare($sql);            $sth->execute();            $result = $sth->fetchAll();            return $result;        } catch (PDOException $e) {            print 'error:' . $e->getMessage();            die;        }    }}

在另外的文件这样调用

<?php require_once 'db.php';$sql = 'select * from user';$dbhelper = new DbHelper;for ($i=0; $i < 10; $i++) {     $res = $dbhelper->query($sql);    // var_dump($res) . PHP_EOL;}

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