How Many Connections are crating here

[Abdullah Rashid]

Below are some file structure of my website. I have removed unnecessary codes from these example codes in order to avoid confusions and larger code chunk.

class: connection.php (collected from internet)

<?php
class connection {
private $_connection;
private static $_instance; //The single instance
private $_host = "localhost";
private $_username = "username";
private $_password = "password";
private $_database = "database";

/*
Get an instance of the Database
@return Instance
*/
public static function getInstance() {
if(!self::$_instance) { // If no instance then make one
self::$_instance = new self();
}
return self::$_instance;
}

// Constructor
private function __construct() {
$this->_connection = new mysqli($this->_host, $this->_username,
$this->_password, $this->_database);
}

// Magic method clone is empty to prevent duplication of connection
private function __clone() { }

// Get mysqli connection
public function getConnection() {
return $this->_connection;
}
}
?>

class: login.php (this class authorize users in the website)

class login extends connection{
private $conn;
private $userid;
public $loggedin;

function __construct($id){
$this->userid = $id;
$this->set_login();
}

private function set_login(){
$this->connect();
$result = $this->conn->query("SELECT status FROM users WHERE userid='".$this->userid.'"');
if($result){
$this->loggedin = true;
}else{
$this->loggedin = false;
}
}

private function connect(){
$this->conn = parent::getInstance()->getConnection();
}
}


phppage: index.php (this page is for testing number of connection)

<?php
spl_autoload_register(function ($class) {
include '../classes/' . $class . '.php';
});
$user = new login("75");
if($user->logged_in){
$db = connection::getInstance();
$conn = $db->getConnection();
$query = 'SHOW STATUS WHERE variable_name LIKE "Threads_%" OR variable_name = "Connections"';
$result = $conn->query($query);
while($row=$result->fetch_assoc()){
echo $row['Variable_name'].' - '.$row['Value'].'<br />';
}
}
?>

the index.php will show the following information about connection:

Connections - 1026572
Threads_cached - 7
Threads_connected - 9
Threads_created - 42943
Threads_running - 2

I am referencing two `$conn` in the above examples, one is inside `login.php` class and the another is in `index.php` page, but from the same `connection.php` class.

I can know the total active connection from `Threads_running` value. But sometimes I can see that the `Threads_running - 2` and sometimes it becomes `Threads_running - 1` while I reload the page.

So, my question to expert is, according to the classes above, is there any possibility to have more than one database connection at a time?

If no, why it is showing `Threads_running - 2` sometimes?