mysql连接池php

class MySQLConnectionPool {
    private $pool = [];
    private $minConnections = 5;
    private $maxConnections = 10;
    private $connectionParams;

    public function __construct($host, $dbname, $user, $password) {
        $this->connectionParams = [
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8mb4',
        ];
        $this->connectionParams[PDO::ATTR_EMULATE_PREPARES] = false;
        $this->connectionParams[PDO::ATTR_STRINGIFY_FETCHES] = false;
        $this->connectionParams[PDO::ATTR_ERRMODE] = PDO::ERRMODE_EXCEPTION;
        $this->connectionParams[PDO::ATTR_DEFAULT_FETCH_MODE] = PDO::FETCH_ASSOC;
        $this->connectionParams[PDO::MYSQL_ATTR_INIT_COMMAND] = 'SET NAMES utf8mb4';

        for ($i = 0; $i < $this->minConnections; $i++) {
            $this->pool[] = new PDO("mysql:host=$host;dbname=$dbname;charset=utf8mb4", $user, $password, $this->connectionParams);
        }
    }

    public function getConnection() {
        if (empty($this->pool)) {
            if (count($this->pool) < $this->maxConnections) {
                $this->pool[] = new PDO("mysql:host={$this->connectionParams['host']};dbname={$this->connectionParams['dbname']};charset=utf8mb4", $this->connectionParams['user'], $this->connectionParams['password'], $this->connectionParams);
            } else {
                throw new Exception('No available connections in the pool.');
            }
        }
        return array_pop($this->pool);
    }

    public function releaseConnection(PDO $connection) {
        $this->pool[] = $connection;
    }
}

// 使用示例
$pool = new MySQLConnectionPool('localhost', 'testdb', 'user', 'password');
$dbh = $pool->getConnection();
try {
    $stmt = $dbh->prepare('SELECT * FROM users WHERE id = :id');
    $stmt->execute(['id' => 1]);
    $result = $stmt->fetch();
    print_r($result);
} catch (Exception $e) {
    echo 'Error: ' . $e->getMessage();
} finally {
    $pool->releaseConnection($dbh);
}