Change SESSION variable to stop "while loop"

Question

I'm new to php and I want to control a php while loop script, using buttons (start/stop), the start button make an ajax call to the start.php script that define $_SESSION['loop'] = TRUE and execute the loop, the stop button make an ajax call to the stop.php script that just change $_SESSION['loop'] to FALSE.

Below is my code so far, but when I hit the stop button I became the alert (success stop) only after the while loop finish looping, which mean the loop didn't break as I was assuming.

I think it's something with the session that is locked while the loop is executing. If so, how to change the $_SESSION['loop'] value and make the loop read that value each time?

index.php

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
    $(document).ready(function(){
        $('#start').click(function(){
            $.ajax({
                url: "start.php"
            });
        });

        $('#stop').click(function(){
            $.ajax({
                url: "stop.php",
                success: function(){
                    alert('success stop');
                },
                error: function(){
                    alert('failure stop');
                }
            });
        });
    });
</script>

<button id="start">Start</button>
<button id="stop">Stop</button>

start.php

<?php
    session_start();
    $_SESSION['loop'] = TRUE;

    ini_set('max_execution_time', 300);
    $i = 0;
    while($i < 100) {

        if ($_SESSION['loop'] == TRUE) {

            //query to save some variables

            // Pause 10s after saving 2
            if ($i != 0 && $i%2 == 0) {
                sleep(10);
            }

            $i++;

        } else {
            break;
        }
    }
?>

stop.php

<?php
    session_start();

    if(isset($_SESSION['loop'])) {
        $_SESSION['loop'] = FALSE;
    }
?>

yes, your loop will not stop after it complete or till the PHP execution time ends, also, the new SESSION value will not be available to the page in the middle of the process... therefore, you can't do something like that — user1646111
– user1646111, Commented Mar 25, 2013 at 13:23
Use a database storage system instead, and keep re-checking inside the loop. IE every if($_SESSION['loop'].. should be a sql select query and $_SESSION['loop']=.. should be an sql update query — Waygood
– Waygood, Commented Mar 25, 2013 at 13:34

grahamj42 · Accepted Answer · 2013-03-25 13:23:55Z

1

Your start and stop operations are in two different sessions, so changing $SESSION in one makes no difference to the other.

answered Mar 25, 2013 at 13:23

grahamj42

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3 Comments

thesubroot Over a year ago

Can I use something like cookies to access the same session so I can change its variable?

grahamj42 Over a year ago

Cookies live in the browser and are exchanged when a page is loaded, so your loop will never see any changes.

Salman Virk Over a year ago

@grahamj42: How do you know they are in two different sessions?

A human being · Accepted Answer · 2013-03-25 13:26:01Z

0

I think, you should use multi-threading for doing such things.

answered Mar 25, 2013 at 13:26

A human being

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Comments

Salman Virk · Accepted Answer · 2013-03-25 13:52:55Z

0

Please take some time to read it:

"Session data is usually stored after your script terminated without the need to call session_write_close(), but as session data is locked to prevent concurrent writes only one script may operate on a session at any time."

http://php.net/manual/en/function.session-write-close.php

Hence, it appears that $_SESSION['loop'] is written to session file at the end.

If you want to explicitly write data to session file, add session_write_close after $_SESSION['loop'] = TRUE. Note, if you need to read/write some session data again in the same script, you need to start the session and then read/write data.

edited Mar 25, 2013 at 13:52

answered Mar 25, 2013 at 13:31

Salman Virk

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