Description:
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We have a web page that refresh 3 images every seconds, we use javascript + dhtml to accomplish this. 

We use a timeout to call the UpdateImage function every second for each of the three images. Since there was a security risk in enabling sending cookies when changing the src attribute of an image, we need to send the Session ID as a GET request because we need our Session variables in test.php to select the right image to send back to the browser.

The calls to change the 3 images are made very close to one another, maybe even at the same time (but it sure is within a few milliseconds). Here's what happen :

1. Call to change the first image - Ok
2. Call to change the second image - Ok, but php change the Session ID after session_start() (why ???).
3. Call to change the third image - Fail, because the Session ID is not good anymore.

What happen is that the third call to the function is made <-before-> the Session ID is changed in the browser cookie, kind of a race condition.


Reproduce code:
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function UpdateImage(IdImage)
{
    var phpsessionid = GetSessionID(); //Get the PHPSESSID value from the cookie.

    document.getElementById(IdImage).src = "http://example.com/test.php?PHPSESSID=" + phpsessionid + "xxxxxxxxx&idimage=id";
}

Expected result:
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We would expect the Session ID not to change between those calls, unless someone can explain why it is changed like that.