Schedly: A job scheduling library for Golang applications

What is it?

Very light weight and flexible task scheduling library for Golang applications without extra dependencies.

Usage

Install

go get github.com/justpresident/schedly

Examples

package main

import (

"fmt"
"github.com/justpresident/schedly"
"time"

)

func main() {
  // Create a scheduler with a tick = second
  sched := schedly.NewScheduler(time.Second).
    SetAligned(true) // start launching tasks at the beginning of their period - e.g.
                     // minutely tasks at the beginning of every minute.
  
   // Print current time every 5 seconds
  sched.Schedule(5*time.Second, "print time", func() {fmt.Print(time.Now())})

  sched.Start()

  sched.WaitUntilStopped() // to wait indefinitely until program exits or someone calls Stop()
}

schedly doesn't take any assumptions and allows you to implement any schedule easily.

Let's define a schedule for our job - every minute of NASDAQ trading time.

  nasdaqTimeSchedule := sched.NewSchedule(time.Minute). // execute tasks minutely
	SetConstraintFunc(isNasdaqTime) // where isNasdaqTime := func(moment time.Time) bool {...} 
  
  sched.AddJob(
    nasdaqTimeSchedule,
    "download TSLA stock price",
    func() { updateQuote("TSLA") },
  )

To stop scheduler from running new tasks:

  ... // do whatever your application needs to do and then call
  sched.Stop() // to stop scheduling new tasks
  // and optionally
  sched.WaitForRunningTasks() // to gracefully wait for all the running tasks to finish

Schedule

Schedule have following configuration options:

SetConstraintFunc() to set up an extra constraint. Example:

sched.NewSchedule(time.Minute).
  SetConstraintFunc(func (t time.Time) {
    return t.Weekday() != time.Sunday
  })

SetAligned(true) to set up aligned feature of the schedule. It is automatically set to true if Aligned property has already been set for scheduler itself. You can enable/disable this property individually per job.

Schedule has following accessors:

schedule.IntervalMode() // returns interval mode setting (read above)
schedule.Aligned() // returns aligned setting (read above)
schedule.Every() // returns launch interval

SetIntervalMode() When IntervalMode is set to false then next job launch time is calculated as 'last job start time' + configured interval. When set to true the interval for launching the job is measured from the finish time of previous launch.

Jobs

The job returned by AddJob or Schedule methods can be further configured:

myJob := sched.Schedule(5*time.Second, "print time", func() {fmt.Print(time.Now())})

/* Avoid parallel runs. If previous run of the job has not finished yet,
 next run will be blocked until it finishes. It simply locks a mutex before starting.
More options of controlling this behaviour will be introduced in next releases.
*/ 
myJob.SetExclusive(true)

// You don't need to assign a job to a variable to configure it. You can do it in one line:
sched.Schedule(...).SetExclusive(true)

Also job has following accessors:

myJob.Name() // returns the name of the job
myJob.LastRun() // returns previous start time. Returns 0 if the job has not been launched yet
myJob.LastFinish() // returns finish time of previous launch. Returns 0 if job has not been launched yet or has not finished yet.
myJob.Exclusive() // returns exclusive launch setting (read above)

How to contribute

Please refer to the contribution guidelines here: /docs/CONTRIBUTING.md

justpresident / schedly