session_abort

To better understand this function you should execute this code first :

<?php
    // First of all choose your path , For e.g. C:/session
    session_save_path('Your Path here !');
    
    session_start();
    
    // Define a Session Variable
    $_SESSION['Key'] = 'value' ;
    
    Var_dump(session_status() == PHP_SESSION_ACTIVE);
    
    // Output : bool(True) , it means you have an open session !
?>

Then you should execute this code :

<?php
    // Choose the path that you used it in first part  
    session_save_path('Your path here');
    
    session_start();
    
    // If you want to close session and keep your original data in your path , you should use session_abort()
    session_abort();
    
    var_dump(session_status()== PHP_SESSION_ACTIVE);
    
    // Output : bool(False) , it means your session closed .
?>

So if you have an open session , session_abort() will simply close it without effecting the external session data , so you can reload your data again from your path that you chose .

session_abort()  closes the current session and discards the changes applied to Session array in the current page  , it doesn't delete the session file 
let me explain with one example. 
page 1.php :
<?php
session_start();
$_SESSION['city']="Sydney";
echo "<a href=\"2.php\"> page2</a>";
?>
when you open this page , a session file is created on the server (to find out where session files are saved run "echo session_save_path()" )  with the name of session_id  and the content of  the variable :

  sess_o22iabs75j93uhc7i4jf1lecjk  (file name)
  city|s:6:"Sydney";               (content)

if we go to 2.php containing this code :

<?php
session_start();
$_SESSION['country']="Australia";
echo session_encode();
session_abort();
session_start();
echo "<br>".session_encode();
?>

when session_abort is executed , the session is closed and the change which here is the 'country' element of Session array is discarded . 

Output : 
city|s:6:"Sydney";country|s:9:"Australia";
city|s:6:"Sydney";