creating schedule task without Cron job

Question

Scheduled task needs to be created but its not possible to use Cron job (there is a warning from hosting provider that \"running the cron Job more than once within a 45-minu

Answer 1

Option A

An easy way to realize it would be to create a file/database entry containing the execution time of your php script:

 1507979485,
    'sendnewsletter.php' => 1507999485
];
?>

And on every request made through your visitors you check the current time and if its higher you include your php script:

 $time) {
    if ($time < time()) {
        // create lock to avoid race conditions
        $lock = 'cache/' . md5($script) . '.lock';
        if (file_exists($lock) || !mkdir($lock)) {
            continue;
        }
        // start your php script
        include($script);
        // now update crons.php
        $crons[ $script ] += 86400; // tomorrow
        file_put_contents('cache/crons.php', '')
        // finally delete lock
        rmdir($lock);
    }
}
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
// image data
$im = imagecreate(1, 1);
$blk = imagecolorallocate($im, 0, 0, 0);
imagecolortransparent($im, $blk);
// image output
header("Content-type: image/gif");
imagegif($im);
// free memory
imagedestroy($im);
?>

Note: It will be rarily called on the exact second, because you do not know when your visitor will open your page (maybe 2 seconds later). So it makes sense to set the new time for the next day not through adding 86400 seconds. Instead use mktime.

Option B

This is a little project I realized in the past, that is similar to @r3wt 's idea, but covers race conditions and works on exact times like a cronjob would do in a scheduler without hitting the max_execution_time. And it works most of the time without the need to resurrect it (as done through visitors in Option A).

Explanation: The script writes a lock file (to avoid race conditions) for the 15th, 30th, 45th and 60th second of a minute:

// cron monitoring
foreach ($allowed_crons as $cron_second) {
    $cron_filename = 'cache/' . $cron_second . '_crnsec_lock';
    // start missing cron requests
    if (!file_exists($cron_filename)) {
        cron_request($cron_second);
    }
    // restart interrupted cron requests
    else if (filemtime($cron_filename) + 90 < time()) {
        rmdir($cron_filename);
        cron_request($cron_second);
    }
}

Every time a lock file is missing the script creates it and uses sleep() to reach the exact second:

if (file_exists($cron_filename) || !mkdir($cron_filename)) {
    return;
}
// add one minute if necessary
$date = new DateTime();
$cron_date = new DateTime();
$cron_date->setTime($cron_date->format('H'), $cron_date->format('i'), $sec);
$diff = $date->diff($cron_date);
if ($diff->invert && $diff->s > 0) {
    $cron_date->setTime($cron_date->format('H'), $cron_date->format('i') + 1, $sec);
}
$diff = $date->diff($cron_date);
// we use sleep() as time_sleep_until() starts one second to early (https://bugs.php.net/bug.php?id=69044)
sleep($diff->s);

After waking up again, it sends a request to itself through fopen():

// note: filter_input returns the unchanged SERVER var (http://php.net/manual/de/function.filter-input.php#99124)
// note: filter_var is unsecure (http://www.d-mueller.de/blog/why-url-validation-with-filter_var-might-not-be-a-good-idea/)
$url = 'http' . isSecure() . '://' . filter_input(INPUT_SERVER, 'HTTP_HOST', FILTER_SANITIZE_URL) . htmlspecialchars($request_uri, ENT_QUOTES, 'UTF-8');
$context = stream_context_create(array(
    'http' => array(
        'timeout' => 1.0
    )
));
// note: return "failed to open stream: HTTP request failed!" because timeout < time_sleep_until
if ($fp = @fopen($url, 'r', false, $context)) {
    fclose($fp);
}
rmdir($cron_filename);

By that it calls itself infinitely and you are able to define different starting times:

if (isset($_GET['cron_second'])) {
    if ($cron_second === 0 && !(date('i') % 15)) {
        mycron('every 15 minutes');
    }
    if ($cron_second === 0 && !(date('i') % 60)) {
        mycron('every hour');
    }
}

Note: It produces 5760 requests per day (4 per minute). Not much, but a cronjob uses much less ressources. If your max_execution_time is high enough you could change it to calling itself only once per minute (1440 requests/day).