Ajax resetting my global variable

Question

I am wondering why I can't read the updated value of $_TEST. It seems that $_TEST is being reset with each Ajax call.

// functions.php
$_TEST = 0; // the variable I want to update  with each Ajax call
if ( is_admin() ) {
add_action( 'wp_ajax_get_global_val', 'get_global_val');
add_action( 'wp_ajax_nopriv_get_global_val', 'get_global_val');
}
function get_global_val() // my Ajax function
{ 
  global $_TEST;    // the value I want to update
  echo $_TEST; // displaying 0 instead of 1
  $_TEST = 1; // update my variable
}

Answer 1

Each time you're making an ajax call, $_TEST = 0; is being evaluated again. You use the options API to manipulate your variable.

function get_global_val() 
{
   $count = get_option( 'mycount' );
   $count++; //or whatever you want to do with it
   update_option( 'mycount', $count );
   die("New value is $count");
}