mysqli_multi_query 是异步的吗?

$databases = array();
$path = '/Path/To/Directory';
$main_link = mysqli_connect('localhost', 'USERNAME', 'PASSWORD');
$files = scandir($path);
$ignore_files = array();

foreach($files as $file)
{
    if (!in_array($file, $ignore_files))
    {
        $database = substr($file, 0, strpos($file,'.'));
        $databases[] = $database;
        mysqli_query($main_link, "DROP DATABASE IF EXISTS $database") or die ("$database 1" . mysqli_error($main_link));
        mysqli_query($main_link, "CREATE DATABASE $database") or die ("$database 2" .mysqli_error($main_link));
        $db_link = mysqli_connect('localhost', 'USERNAME', 'PASSWORD', $database);
        //In here a whole database dump with scheam + data is executed. 
        mysqli_multi_query($db_link, file_get_contents($path.'/'.$file)) or die ("$database 4" .mysqli_error($db_link));        
    }   
}

当运行这个脚本时，它完成得非常快(返回浏览器)，但在浏览器说它完成后它仍在运行查询.这是为什么?

mysqli_multi_query($db_link, file_get_contents($path.'/'.$file)) or die ("$database 4" .mysqli_error($db_link)); 

do {
    if($result = mysqli_store_result($db_link)){
        mysqli_free_result($result);
    }
} while(mysqli_next_result($db_link));

if(mysqli_error($db_link)) {
    die(mysqli_error($db_link));
}