通过AJAX发布并保存php会话

Question

I'm trying to save value to php session using post into jquery. Below jquery code:

$.ajax({
    url: callPHPFuncURL,
    type: 'POST',
    async: false,
    timeout: 30000,
    data: {methodName: 'moveschedulerhorizont',
        forward: forward
    },
    dataType: 'json'
}).done(function (data) {
    if (data.success === true) {
        isOK = data.success;
    }
    isOK = true;
});

Below moveschedulerhorizont method:

$forward = $_POST['forward'];

$scheduler = new Scheduler();
$isOK = $scheduler->set_firstDate($forward);

And below set_firstDate method:

$dt = new DateTime($this->firstDateTime);
$dt->add(new DateInterval('P' . ($this->skipHorizont * 7) . 'D'));
$_SESSION['StartDate'] = $dt->format('Y-m-d');

The part that calculates date returns the correct value. But value isn't save to session. Session_start() is called in other part of code.

The strangest this is that i save startDate to session, but when page is generated. But later when i use jquery it doesn't work :(