My AJAX calls are not running simultaneously

Question

When I click button 1 it starts the Python file. When I click button 2 it waits for button 1's AJAX call to complete its execution. I don't want that.

Button 2 creates a text file to kill that infinite Python program (which checks for the existence of that text file at regular intervals).

In short, I am not able to create a text file (button 2's AJAX) when my Python file is running (button1's AJAX)

$(document).ready(function() {
  $("#s1").on("click", function(e) {
    console.log("hi s1");
    e.preventDefault();

    $.ajax({
      async: true,
      url: "file1.php",
      type: "GET",
      data: {
        action: "start"
      },
      success: function(response) {
        console.log("The ajax request succeeded!");
      }
    });
  });

  $("#s2").on("click", function(e) {
    console.log("hi s2");
    e.preventDefault();

    $.ajax({
      async: true,
      url: "file1.php",
      type: "GET",
      data: {
        action: "start2"
      },
      success: function(response) {
        console.log("The ajax request succeeded!");
      }
    });
  });
});

// php code for button1 
if (isset($_GET['action']) && strcasecmp($_GET['action'], "start1") == 0)
{
  $command = escapeshellcmd("python demo.py");
  // python file is a infite loop always running program
  $output = shell_exec($command);
  // echo $output;
}

// php code for button2
if (isset($_GET['action']) && strcasecmp($_GET['action'], "start2") == 0)
{
  echo "Activity stopped";
  $myfile = fopen("demo.txt", "w");
  $txt = "Example\n";
  fwrite($myfile, $txt);
  fclose($myfile);
}