golang的cron实现

smart_yh · · 978 次点击 · · 开始浏览    
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cron定时计划任务,golang的cron开源项目代码分析:https://github.com/robfig/cron

package cron

import (
	"log"
	"runtime"
	"sort"
	"time"
)

// Cron keeps track of any number of entries, invoking the associated func as
// specified by the schedule. It may be started, stopped, and the entries may
// be inspected while running.
type Cron struct {
	entries  []*Entry //Entry是所有任务封装的结构
	stop     chan struct{} //关闭flag的channel
	add      chan *Entry   //新增的Entry
	snapshot chan []*Entry //Entry的备份
	running  bool //开启flag
	ErrorLog *log.Logger
	location *time.Location
}

// Job is an interface for submitted cron jobs.
type Job interface {
	Run() //Job只有一个Run方法
}

// The Schedule describes a job's duty cycle.
type Schedule interface {
	// Return the next activation time, later than the given time.
	// Next is invoked initially, and then each time the job is run.
	Next(time.Time) time.Time //调度选取下一次执行的时候,整个流程执行非常关键不住
}

// Entry consists of a schedule and the func to execute on that schedule.
type Entry struct {
	// The schedule on which this job should be run.
	Schedule Schedule

	// The next time the job will run. This is the zero time if Cron has not been
	// started or this entry's schedule is unsatisfiable
	Next time.Time //下一次运行的时间

	// The last time this job was run. This is the zero time if the job has never
	// been run.
	Prev time.Time //上一次运行的时间

	// The Job to run.
	Job Job
}

// byTime is a wrapper for sorting the entry array by time
// (with zero time at the end).
type byTime []*Entry

func (s byTime) Len() int      { return len(s) }
func (s byTime) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s byTime) Less(i, j int) bool {
	// 比较时间,两个都是0的时候直接返回false,0比任何时间优先级高
	if s[i].Next.IsZero() {
		return false
	}
	if s[j].Next.IsZero() {
		return true
	}
	return s[i].Next.Before(s[j].Next)
}

// New returns a new Cron job runner, in the Local time zone.
func New() *Cron {
	return NewWithLocation(time.Now().Location())
}

// NewWithLocation returns a new Cron job runner.
func NewWithLocation(location *time.Location) *Cron {
	return &Cron{
		entries:  nil,
		add:      make(chan *Entry), //新增entry的channel
		stop:     make(chan struct{}),
		snapshot: make(chan []*Entry),
		running:  false,
		ErrorLog: nil,
		location: location, //时间
	}
}

// A wrapper that turns a func() into a cron.Job
type FuncJob func()

func (f FuncJob) Run() { f() }

// AddFunc adds a func to the Cron to be run on the given schedule.
func (c *Cron) AddFunc(spec string, cmd func()) error {
	return c.AddJob(spec, FuncJob(cmd))
}

// AddJob adds a Job to the Cron to be run on the given schedule.
func (c *Cron) AddJob(spec string, cmd Job) error {
	schedule, err := Parse(spec)
	if err != nil {
		return err
	}
	c.Schedule(schedule, cmd)
	return nil
}

// Schedule adds a Job to the Cron to be run on the given schedule.
func (c *Cron) Schedule(schedule Schedule, cmd Job) {
	entry := &Entry{
		Schedule: schedule,
		Job:      cmd,
	}
	if !c.running {
		c.entries = append(c.entries, entry)
		return
	}

	c.add <- entry
}

//当前运行的所有Entry的一份拷贝,方便测试和跟踪
func (c *Cron) Entries() []*Entry {
	if c.running {
		//先传一个nil,触发channel的读时间,run的协程复制entry,然后读取出所有的entry
		c.snapshot <- nil
		x := <-c.snapshot
		return x
	}
	return c.entrySnapshot()
}

// Location gets the time zone location
func (c *Cron) Location() *time.Location {
	return c.location
}

//Start方法和Run方法的区别就是在不在单独的go-routine里面运行
// Start the cron scheduler in its own go-routine, or no-op if already started.
func (c *Cron) Start() {
	if c.running {
		return
	}
	c.running = true
	go c.run()
}

// Run the cron scheduler, or no-op if already running.
func (c *Cron) Run() {
	if c.running {
		return
	}
	//开始cron的运行
	c.running = true
	c.run()
}

func (c *Cron) runWithRecovery(j Job) {
	defer func() {
		//运行job panic的时候日志记录栈信息
		if r := recover(); r != nil {
			const size = 64 << 10
			buf := make([]byte, size)
			buf = buf[:runtime.Stack(buf, false)]
			c.logf("cron: panic running job: %v\n%s", r, buf)
		}
	}()
	j.Run()
}

// Run the scheduler. this is private just due to the need to synchronize
// access to the 'running' state variable.
func (c *Cron) run() {
	// Figure out the next activation times for each entry.
	now := c.now()
	for _, entry := range c.entries {
		entry.Next = entry.Schedule.Next(now)
	}

	for {
		// 从小到大的排序entry
		sort.Sort(byTime(c.entries))

		var timer *time.Timer
		if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
			// 没有entry的时候设置超大的timer,依然可以处理stop
			timer = time.NewTimer(100000 * time.Hour)
		} else {
			timer = time.NewTimer(c.entries[0].Next.Sub(now))
		}

		for {
			select {
			case now = <-timer.C:
				now = now.In(c.location)
				// 运行比now时间小的entry
				for _, e := range c.entries {
					if e.Next.After(now) || e.Next.IsZero() {
						break
					}
					//执行任务Job
					go c.runWithRecovery(e.Job)
					e.Prev = e.Next
					e.Next = e.Schedule.Next(now)
				}

			case newEntry := <-c.add:
				//新增entry时候,停掉上一次的timer,
				timer.Stop()
				now = c.now()
				newEntry.Next = newEntry.Schedule.Next(now)
				c.entries = append(c.entries, newEntry)

			case <-c.snapshot:
				c.snapshot <- c.entrySnapshot()
				continue

			case <-c.stop:
				timer.Stop()
				return
			}

			break
		}
	}
}

// Logs an error to stderr or to the configured error log
func (c *Cron) logf(format string, args ...interface{}) {
	if c.ErrorLog != nil {
		c.ErrorLog.Printf(format, args...)
	} else {
		log.Printf(format, args...)
	}
}

// Stop stops the cron scheduler if it is running; otherwise it does nothing.
func (c *Cron) Stop() {
	if !c.running {
		return
	}
	c.stop <- struct{}{}
	c.running = false
}

// entrySnapshot returns a copy of the current cron entry list.
func (c *Cron) entrySnapshot() []*Entry {
	entries := []*Entry{}
	for _, e := range c.entries {
		entries = append(entries, &Entry{
			Schedule: e.Schedule,
			Next:     e.Next,
			Prev:     e.Prev,
			Job:      e.Job,
		})
	}
	return entries
}

// now returns current time in c location
func (c *Cron) now() time.Time {
	return time.Now().In(c.location)
}

其实关键就是Schedule的Next的方法的具体实现


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本文来自:开源中国博客

感谢作者:smart_yh

查看原文:golang的cron实现

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