robfig_cron

cron

Upgrading to v3 (June 2019)

cron v3 is a major upgrade to the library that addresses all outstanding bugs, feature requests, and rough edges. 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.

New features:

• Extensible, key/value logging via an interface that complies with the github.com/go-logr/logr project.

• The new Chain & JobWrapper types allow you to install "interceptors" to add cross-cutting behavior like the following:

  • Recover any panics from jobs (activated by default)
  • Delay a job's execution if the previous run hasn't completed yet
  • Skip a job's execution if the previous run hasn't completed yet
  • Log each job's invocations
  • Notification when jobs are completed

To avoid breaking backward compatibility, Entry.Job continues to be the value that was submitted, and Entry has a new WrappedJob property which is the one that is actually run.

It is backwards incompatible with both v1 and v2. These updates are 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.

• By default, cron will no longer recover panics in jobs that it runs. Recovering can be surprising (see issue #192) and seems to be at odds with typical behavior of libraries. Relatedly, the cron.WithPanicLogger option has been removed to accommodate the more general JobWrapper type.

UPDATING: To opt into panic recovery and configure the panic logger:

  cron.New(cron.WithChain(
      cron.Recover(logger),  // or use cron.DefaultLogger
  ))

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. Now, the "standard" format is the default format accepted, and the Quartz format is opt-in.