reset next job execution if the system time has been moved backwards

[drakkan]

Suppose you have a job scheduled every minute.

The current time is 15:00:00 and for reasons outside our control it is set to 17:00:00, the job runs as expected and "Next" will be set to 17:01:00.
If the system clock returns to the correct time and so now is, for example, 15:01:00, when we calculate the duration of the timer here

cron/cron.go

Line 259 in bc59245

timer = time.NewTimer(c.entries[0].Next.Sub(now))

we will have something like 2 hours and then no job runs for 2 hours.

This patch fixes the issue. Thank you

[CybotTM]

Solution available in maintained fork

This feature has been implemented in netresearch/go-cron, a maintained fork of this library.

Implementation: The scheduler now gracefully handles system time moving backwards (e.g., NTP corrections, manual clock adjustments). When time goes backwards, entries are re-evaluated against the new time to ensure correct scheduling.

How to migrate:

// Change import from:
import "github.com/robfig/cron/v3"

// To:
import cron "github.com/netresearch/go-cron"

The API is 100% backward compatible. See the migration guide for details.

Related: netresearch#52