cron

DRAFT - Upgrading to v3

cron v3 is a major upgrade to the library that addresses all outstanding bugs, feature requests, and clarifications around usage. It is based on a merge of master which contains various fixes to issues found over the years and the v2 branch which contains some backwards-incompatible features like the ability to remove cron jobs. In addition, v3 adds support for Go Modules and cleans up rough edges like the timezone support.

It is currently IN DEVELOPMENT and will be considered released once a 3.0 version is tagged. It is backwards INCOMPATIBLE with both the v1 and v2 branches.

Updates required:

• The v1 branch accepted an optional seconds field at the beginning of the cron spec. This is non-standard and has led to a lot of confusion. The new default parser conforms to the standard as described by the Cron wikipedia page.

  UPDATING: To retain the old behavior, construct your Cron with a custom parser:

  // Seconds field, required
  cron.New(cron.WithSeconds())
  
  // Seconds field, optional
  cron.New(
      cron.WithParser(
          cron.SecondOptional | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor))
  

• The Cron type now accepts functional options on construction rather than the ad-hoc behavior modification mechanisms before (setting a field, calling a setter).

  UPDATING: Code that sets Cron.ErrorLogger or calls Cron.SetLocation must be updated to provide those values on construction.

• CRON_TZ is now the recommended way to specify the timezone of a single schedule, which is sanctioned by the specification. The legacy "TZ=" prefix will continue to be supported since it is unambiguous and easy to do so.

  UPDATING: No update is required.

Planned updates before calling v3 done:

• Job "Interceptors" (name tbd), which make it easy for callers to mix desired behavior like the following:

  • Recover any panics from jobs
  • Block this job if the previous run hasn't completed yet
  • Logging job invocations
  • Notification when jobs are completed

• Fix all open bugs

Background - Cron spec format

There are two cron spec formats in common usage:

• The "standard" cron format, described on the Cron wikipedia page and used by the cron Linux system utility.

• The cron format used by the Quartz Scheduler, commonly used for scheduled jobs in Java software

The original version of this package included an optional "seconds" field, which made it incompatible with both of these formats. Instead, the schedule parser has been extended to support both types.