Implement catch-up behavior for cron jobs

[intersel]

Why it is needed

When there is a server downtime or when the system cron (calling cron.php) is stopped for any reason, scheduled jobs may accumulate delay.

In the current implementation, the next run (nextrun) is always calculated based on the previous nextrun value. If this value is already in the past, the new nextrun can also remain in the past.

This can lead to repeated immediate executions ("catch-up loops") until the scheduler catches up with the current time. In some cases, this may cause unnecessary load or unexpected behavior, especially for jobs that are not designed to run multiple times in quick succession.

This change introduces an option to control this behavior:

• either keep the existing catch-up mechanism,
• or reschedule jobs from the current time, avoiding execution of missed runs.

This provides safer and more predictable behavior for most use cases while preserving backward compatibility.

What this PR does

Add a cron_catchup system option to control how missed executions are handled.

When disabled, cronjobs are always rescheduled from the current time, avoiding catch-up loops after downtime.

When enabled, the existing behavior is preserved, with a safeguard against outdated nextrun values to prevent infinite execution loops.

[Jako]

Maybe it is better to calculate the nextrun with a do/while loop until the nextrun is in the future. Then the additional option is not needed.

[intersel]

I get the idea, but wouldn’t this risk shortening the effective interval between runs compared to the configured delay?

[Jako]

Something like this:

            if ($this->cronmanager->getOption('daylight_saving') && $cronjob->get('minutes') > 60) {
                do {
                    $rundatetime = date('Y-m-d H:i:s', strtotime($cronjob->get('minutes') . ' minutes', (strtotime($rundatetime))));
                } while (strtotime($rundatetime) < time());
                $cronjob->set('nextrun', $rundatetime);
            } else {
                do {
                    $rundatetime = date('Y-m-d H:i:s', (strtotime($rundatetime) + ($cronjob->get('minutes') * 60)));
                } while (strtotime($rundatetime) < time());
                $cronjob->set('nextrun', $rundatetime);
            }

Then the interval between two runs remains the same and just some runs are not executed.

[Jako]

Is this code right for you?

[intersel]

sounds good... not tested yet
Do you want me to redo the PR?

[Jako]

It would be nice, if you have time to test the suggested code.

[intersel]

I'll do my best to give you feedback in the next days...