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PODead Man's Switch in PHP/Python
 

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    <p>So this is as much a theoretical question as a language-specific one, but consider this:</p> <p>I need PHP to execute a rather system-intensive process (using PHP <code>exec();</code>) that will be running in the background, but then when a user leaves that specific page, the process will be killed. </p> <p>I quickly realized that a dead man's switch would be an easy way to implement this since I'm not making use of any session variables or other server-side variables, which could end up looking like:</p> <pre><code>if($_SERVER['REQUEST_URI'] !== 'page_with_session.php'){ //Instead of 'session_destroy();' this would be used to kill said process } </code></pre> <p>In any case, a while loop in PHP, resetting a timer in a Python script or re-calling said script every 15 seconds so that it doesn't get to the end and kill the process. However, when the user leaves the page, the script will have been called but not able to reset before killing the process.</p> <p>Are there any gaping holes in this idea? If not, how would the implementation in PHP/JS look? The order I see it working in would be:</p> <ol> <li>Page is hit by user</li> <li><code>&lt;?php exec('killer.py') ?&gt;</code></li> <li>killer.py: <ol> <li>Listen for 20 seconds - If no response...</li> <li><code>os.system('pkill process')</code></li> </ol></li> <li><code>&lt;?php while(true){sleep(15); exec('killer.py no_wait_dont');} ?&gt;</code></li> </ol> <p>Any thoughts you guys have would be greatly appreciated!</p> <p>Mason</p>
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    1. COHow do you plan to detect that the user left the page? Obviously they might leave the page AND your site altogether - your `if` statement isn't going to do you much good in that case.
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    2. CO@Madbreaks was typing at the same time as me ... Anyway, I'd think you would need some Javascript to ping the server every 15 seconds (maybe less to allow for lag), but then what happens if the connection goes down temporarily, but the user is still on the page? Then, if the connection comes up before the user leaves, your process will have been killed, but from the user's perspective they never left.
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    3. CO@Madbreaks - This is a way to circumvent detecting users leaving the page by setting script that will kill the process if it isn't pinged within a certain amount of time. Even then, if they were to leave both, the server would complete the requested script and exit normally.
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