聊聊dkron的Scheduler

序

本文主要研究一下dkron的Scheduler

Scheduler

// Scheduler represents a dkron scheduler instance, it stores the cron engine
// and the related parameters.
type Scheduler struct {
    Cron        *cron.Cron
    Started     bool
    EntryJobMap sync.Map
}

// NewScheduler creates a new Scheduler instance
func NewScheduler() *Scheduler {
    schedulerStarted.Set(0)
    return &Scheduler{
        Cron:        nil,
        Started:     false,
        EntryJobMap: sync.Map{},
    }
}

// Start the cron scheduler, adding its corresponding jobs and
// executing them on time.
func (s *Scheduler) Start(jobs []*Job, agent *Agent) error {
    s.Cron = cron.New(cron.WithParser(extcron.NewParser()))

    metrics.IncrCounter([]string{"scheduler", "start"}, 1)
    for _, job := range jobs {
        job.Agent = agent
        s.AddJob(job)
    }
    s.Cron.Start()
    s.Started = true
    schedulerStarted.Set(1)

    return nil
}

// Stop stops the scheduler effectively not running any job.
func (s *Scheduler) Stop() {
    if s.Started {
        log.Debug("scheduler: Stopping scheduler")
        s.Cron.Stop()
        s.Started = false
        // Keep Cron exists and let the jobs which have been scheduled can continue to finish,
        // even the node's leadership will be revoked.
        // Ignore the running jobs and make s.Cron to nil may cause whole process crashed.
        //s.Cron = nil

        // expvars
        cronInspect.Do(func(kv expvar.KeyValue) {
            kv.Value = nil
        })
    }
    schedulerStarted.Set(0)
}

// Restart the scheduler
func (s *Scheduler) Restart(jobs []*Job, agent *Agent) {
    s.Stop()
    s.ClearCron()
    s.Start(jobs, agent)
}

// Clear cron separately, this can only be called when agent will be stop.
func (s *Scheduler) ClearCron() {
    s.Cron = nil
}

Scheduler定义了Cron、Started、EntryJobMap属性；NewScheduler方法创建默认的Scheduler；Start方法遍历jobs，挨个设置job.Agent，然后添加到Scheduler中，之后执行Scheduler.Cron.Start()；Stop方法执行Scheduler.Cron.Stop()；Restart方法执行Stop、ClearCron、Start方法；ClearCron设置Cron为nil

AddJob

// AddJob Adds a job to the cron scheduler
func (s *Scheduler) AddJob(job *Job) error {
    // Check if the job is already set and remove it if exists
    if _, ok := s.EntryJobMap.Load(job.Name); ok {
        s.RemoveJob(job)
    }

    if job.Disabled || job.ParentJob != "" {
        return nil
    }

    log.WithFields(logrus.Fields{
        "job": job.Name,
    }).Debug("scheduler: Adding job to cron")

    // If Timezone is set on the job, and not explicitly in its schedule,
    // AND its not a descriptor (that don't support timezones), add the
    // timezone to the schedule so robfig/cron knows about it.
    schedule := job.Schedule
    if job.Timezone != "" &&
        !strings.HasPrefix(schedule, "@") &&
        !strings.HasPrefix(schedule, "TZ=") &&
        !strings.HasPrefix(schedule, "CRON_TZ=") {
        schedule = "CRON_TZ=" + job.Timezone + " " + schedule
    }

    id, err := s.Cron.AddJob(schedule, job)
    if err != nil {
        return err
    }
    s.EntryJobMap.Store(job.Name, id)

    cronInspect.Set(job.Name, job)
    metrics.IncrCounterWithLabels([]string{"scheduler", "job_add"}, 1, []metrics.Label{{Name: "job", Value: job.Name}})

    return nil
}

AddJob方法先移除EntryJobMap中的同名job，然后执行Cron.AddJob(schedule, job)，最后存储到EntryJobMap

RemoveJob

// RemoveJob removes a job from the cron scheduler
func (s *Scheduler) RemoveJob(job *Job) {
    log.WithFields(logrus.Fields{
        "job": job.Name,
    }).Debug("scheduler: Removing job from cron")
    if v, ok := s.EntryJobMap.Load(job.Name); ok {
        s.Cron.Remove(v.(cron.EntryID))
        s.EntryJobMap.Delete(job.Name)

        cronInspect.Delete(job.Name)
        metrics.IncrCounterWithLabels([]string{"scheduler", "job_delete"}, 1, []metrics.Label{{Name: "job", Value: job.Name}})
    }
}

RemoveJob方法先从EntryJobMap移除同名job，然后执行cronInspect.Delete(job.Name)

小结

dkron的Scheduler定义了Cron、Started、EntryJobMap属性；NewScheduler方法创建默认的Scheduler；它提供了Start、Stop、Restart、ClearCron、AddJob、RemoveJob方法。

doc

• dkron