go-quartz

A minimalistic and zero-dependency scheduling library for Go.

About

The implementation is inspired by the design of the Quartz Java scheduler.

The core scheduler component can be used to manage scheduled jobs (tasks) using triggers. The implementation of the cron trigger fully supports the Quartz cron expression format and can be used independently to calculate a future time given the previous execution time.

If you need to run multiple instances of the scheduler, see the distributed mode section for guidance.

Library building blocks

Scheduler interface

type Scheduler interface {
	// Start starts the scheduler. The scheduler will run until
	// the Stop method is called or the context is canceled. Use
	// the Wait method to block until all running jobs have completed.
	Start(context.Context)

	// IsStarted determines whether the scheduler has been started.
	IsStarted() bool

	// ScheduleJob schedules a job using the provided Trigger.
	ScheduleJob(jobDetail *JobDetail, trigger Trigger) error

	// GetJobKeys returns the keys of scheduled jobs.
	// For a job key to be returned, the job must satisfy all of the
	// matchers specified.
	// Given no matchers, it returns the keys of all scheduled jobs.
	GetJobKeys(...Matcher[ScheduledJob]) ([]*JobKey, error)

	// GetScheduledJob returns the scheduled job with the specified key.
	GetScheduledJob(jobKey *JobKey) (ScheduledJob, error)

	// DeleteJob removes the job with the specified key from the
	// scheduler's execution queue.
	DeleteJob(jobKey *JobKey) error

	// PauseJob suspends the job with the specified key from being
	// executed by the scheduler.
	PauseJob(jobKey *JobKey) error

	// ResumeJob restarts the suspended job with the specified key.
	ResumeJob(jobKey *JobKey) error

	// Clear removes all of the scheduled jobs.
	Clear() error

	// Wait blocks until the scheduler stops running and all jobs
	// have returned. Wait will return when the context passed to
	// it has expired. Until the context passed to start is
	// cancelled or Stop is called directly.
	Wait(context.Context)

	// Stop shutdowns the scheduler.
	Stop()
}

Implemented Schedulers

• StdScheduler

Trigger interface

type Trigger interface {
	// NextFireTime returns the next time at which the Trigger is scheduled to fire.
	NextFireTime(prev int64) (int64, error)

	// Description returns the description of the Trigger.
	Description() string
}

Implemented Triggers

• CronTrigger
• SimpleTrigger
• RunOnceTrigger

Job interface

Any type that implements it can be scheduled.

type Job interface {
	// Execute is called by a Scheduler when the Trigger associated with this job fires.
	Execute(context.Context) error

	// Description returns the description of the Job.
	Description() string
}

Several common Job implementations can be found in the job package.

Cron expression format

Field Name	Mandatory	Allowed Values	Allowed Special Characters
Seconds	YES	0-59	, - * /
Minutes	YES	0-59	, - * /
Hours	YES	0-23	, - * /
Day of month	YES	1-31	, - * ? / L W
Month	YES	1-12 or JAN-DEC	, - * /
Day of week	YES	1-7 or SUN-SAT	, - * ? / L #
Year	NO	empty, 1970-	, - * /

Special characters

• *: All values in a field (e.g., * in minutes = "every minute").
• ?: No specific value; use when specifying one of two related fields (e.g., "10" in day-of- month, ? in day-of-week).
• -: Range of values (e.g., 10-12 in hour = "hours 10, 11, and 12").
• ,: List of values (e.g., MON,WED,FRI in day-of-week = "Monday, Wednesday, Friday").
• /: Increments (e.g., 0/15 in seconds = "0, 15, 30, 45"; 1/3 in day-of-month = "every 3 days from the 1st").
• L: Last day; meaning varies by field. Ranges or lists are not allowed with L.
  • Day-of-month: Last day of the month (e.g, L-3 is the third to last day of the month).
  • Day-of-week: Last day of the week (7 or SAT) when alone; "last xxx day" when used after another value (e.g., 6L = "last Friday").
• W: Nearest weekday in the month to the given day (e.g., 15W = "nearest weekday to the 15th"). If 1W on Saturday, it fires Monday the 3rd. W only applies to a single day, not ranges or lists.
• #: Nth weekday of the month (e.g., 6#3 = "third Friday"; 2#1 = "first Monday"). Firing does not occur if that nth weekday does not exist in the month.

¹ The L and W characters can also be combined in the day-of-month field to yield LW, which translates to "last weekday of the month".

² The names of months and days of the week are not case-sensitive. MON is the same as mon.

Distributed mode

The scheduler can use its own implementation of quartz.JobQueue to allow state sharing.
An example implementation of the job queue using the file system as a persistence layer can be found here.

Usage example

package main

import (
	"context"
	"log/slog"
	"net/http"
	"os"
	"time"

	"github.com/reugn/go-quartz/job"
	"github.com/reugn/go-quartz/logger"
	"github.com/reugn/go-quartz/quartz"
)

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	// create a scheduler using the logger configuration option
	slogLogger := slog.New(slog.NewTextHandler(os.Stdout, nil))
	scheduler, _ := quartz.NewStdScheduler(quartz.WithLogger(logger.NewSlogLogger(ctx, slogLogger)))

	// start the scheduler
	scheduler.Start(ctx)

	// create jobs
	cronTrigger, _ := quartz.NewCronTrigger("1/5 * * * * *")
	shellJob := job.NewShellJob("ls -la")

	request, _ := http.NewRequest(http.MethodGet, "https://worldtimeapi.org/api/timezone/utc", nil)
	curlJob := job.NewCurlJob(request)

	functionJob := job.NewFunctionJob(func(_ context.Context) (int, error) { return 1, nil })

	// register the jobs with the scheduler
	_ = scheduler.ScheduleJob(quartz.NewJobDetail(shellJob, quartz.NewJobKey("shellJob")),
		cronTrigger)
	_ = scheduler.ScheduleJob(quartz.NewJobDetail(curlJob, quartz.NewJobKey("curlJob")),
		quartz.NewSimpleTrigger(7*time.Second))
	_ = scheduler.ScheduleJob(quartz.NewJobDetail(functionJob, quartz.NewJobKey("functionJob")),
		quartz.NewSimpleTrigger(5*time.Second))

	// stop the scheduler
	scheduler.Stop()

	// wait for all workers to exit
	scheduler.Wait(ctx)
}

See the examples directory for additional code samples.

License

Licensed under the MIT License.