can cron job be used to show notification in php web

Question

I have following scenario. When any complaint opened for job isn't completed within 48 hours and if that complaint is nearing 48 hours without completion, popup or notification should be there in backend before the time limit(say 1 hour before). I am thinking of doing cron job(run every hour).My problem is how to do the notification in cron job. Any suggestion will be welcome.

Answer 1

The cron job should not be connecting to the pages; it should be the reverse: use the backend pages themselves to check for job completion. You can use Server-Sent Events (SSE) for this. The process would be:

1 Backend pages (Javascript) subscribe to an SSE channel and show a popup when the PHP script emits an event

var source = new EventSource("job_checker.php");
source.onmessage = function(event) {
    //event contains the job info and deadline. you can display it
    var jobDetails = JSON.parse(event);
    ...
};

2 The PHP job_checker.php can run through a loop for a set amount of time, checking for job completion:

<?php
$time_limit = 300; //300 seconds
$time_spent = 0;
while($time_spent < $time_limit){
    sleep(30); //sleep for 30 seconds
    $time_spent += 30;
    //check DB for job completion and deadline.
    //if you find a job, emit an SSE to the browser
    if($event_found){
        header('Content-Type: text/event-stream');
        header('Cache-Control: no-cache'); 
        echo "data: ". json_encode($event_found)."\n\n";
        flush();
    }
}

The PHP script will keep working for 300 seconds. If it finds an event, it will emit data and the browser will get it. After 300 seconds, the script will die. If the user still has the admin page open, the browser will automatically reconnect. If the user has closed the page, the resources will be freed.

More docs from Mozilla: (thanks to Alok Patel for the link)