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
