On AJAX call session is destroying WordPress plugin - php

Question

I am calling an AJAX function from WordPress plugin through admin-ajax.php. But when the request is send, its destroying the session.
I have an array where data is saved on every request, but on every request previous data is destroyed.
AJAX code i am calling:
function cartbox()
{
var url = {
'action':'my_cart_action',
'rnd':Math.random(),
};
$.ajax({
type:'POST',
data:url,
url: "http://localhost/vmlogic/wp-admin/admin-ajax.php",
success : function(response)
{
$("#cartdiv").html(response);
}
});
}
On plugin index file i am calling this:
class cloud_calculator{
// Call a cation on link click
function cloud_calculator()
{
add_action('init' , array($this,'cloud_init'));
}
public function cloud_init()
{
add_action('wp_head' , array($this, 'plugin_jquery_func'));
add_action('admin_menu', array($this,'my_menu'));
add_shortcode('cloud_calculator', array($this,'my_calculator'));
add_action('the_content', array($this,'the_content_action'));
add_action( 'wp_ajax_my_unique_action', array($this,'my_unique_action_callback'));
add_action( 'wp_ajax_nopriv_my_unique_action', array($this,'my_unique_action_callback'));
add_action( 'wp_ajax_my_cart_action', array($this,'my_cart_action_callback'));
add_action( 'wp_ajax_nopriv_my_cart_action', array($this,'my_cart_action_callback'));
}
public function plugin_jquery_func()
{
$plugins_url = plugins_url().'/cloud-calculaor/';
?>
<script type="application/javascript">
var PluginUrlJs = '<?php echo $plugins_url ;?>';
</script>
<?php }
public function the_content_action($content)
{
$content = str_replace('[cloud_calculator]',do_shortcode('[cloud_calculator]') ,$content );
return $content;
}
// Menu call function
public function my_menu() {
add_menu_page('Cloud Calculator', 'Cloud Calculator', 'manage_options', 'cloud-calculaor/cloud-calculaor.php', array($this, 'my_function'));
}
// action to call on admin menu
public function my_function() {
wp_enqueue_style('style', '/wp-content/plugins/cloud-calculaor/style/admincalculator.css');
echo
'<div class="wrap">
<h2>Cloud Calculator</h2>
<div class="plugincode">
<div style=" padding:10px 10px 10px 50px;">
<p style="margin:5px 0px">
To Insert <strong>CLOUD CALCULATOR</strong> shortcode inside a page or post:<br>
<br>
Use: <code><strong>[cloud_calculator]</strong></code><br>
<br>
For more queries contact the administrator!<br>
</p>
</div>
</div>
</div>
';
}