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package cron
import (
"context"
"sort"
"sync"
"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
chain Chain
stop chan struct{}
add chan *Entry
remove chan EntryID
snapshot chan chan []Entry
running bool
logger Logger
runningMu sync.Mutex
location *time.Location
parser ScheduleParser
nextID EntryID
jobWaiter sync.WaitGroup
}
// ScheduleParser is an interface for schedule spec parsers that return a Schedule
type ScheduleParser interface {
Parse(spec string) (Schedule, error)
}
// Job is an interface for submitted cron jobs.
type Job interface {
Run()
}
// Schedule describes a job's duty cycle.
type Schedule interface {
// Next returns 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
}
// EntryID identifies an entry within a Cron instance
type EntryID int
// Entry consists of a schedule and the func to execute on that schedule.
type Entry struct {
// ID is the cron-assigned ID of this entry, which may be used to look up a
// snapshot or remove it.
ID EntryID
// Schedule on which this job should be run.
Schedule Schedule
// Next time the job will run, or the zero time if Cron has not been
// started or this entry's schedule is unsatisfiable
Next time.Time
// Prev is the last time this job was run, or the zero time if never.
Prev time.Time
// WrappedJob is the thing to run when the Schedule is activated.
WrappedJob Job
// Job is the thing that was submitted to cron.
// It is kept around so that user code that needs to get at the job later,
// e.g. via Entries() can do so.
Job Job
}
// Valid returns true if this is not the zero entry.
func (e Entry) Valid() bool { return e.ID != 0 }
// 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 {
// Two zero times should return false.
// Otherwise, zero is "greater" than any other time.
// (To sort it at the end of the list.)
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, modified by the given options.
//
// Available Settings
//
// Time Zone
// Description: The time zone in which schedules are interpreted
// Default: time.Local
//
// Parser
// Description: Parser converts cron spec strings into cron.Schedules.
// Default: Accepts this spec: https://en.wikipedia.org/wiki/Cron
//
// Chain
// Description: Wrap submitted jobs to customize behavior.
// Default: A chain that recovers panics and logs them to stderr.
//
// See "cron.With*" to modify the default behavior.
func New(opts ...Option) *Cron {
c := &Cron{
entries: nil,
chain: NewChain(),
add: make(chan *Entry),
stop: make(chan struct{}),
snapshot: make(chan chan []Entry),
remove: make(chan EntryID),
running: false,
runningMu: sync.Mutex{},
logger: DefaultLogger,
location: time.Local,
parser: standardParser,
}
for _, opt := range opts {
opt(c)
}
return c
}
// FuncJob is 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.
// The spec is parsed using the time zone of this Cron instance as the default.
// An opaque ID is returned that can be used to later remove it.
func (c *Cron) AddFunc(spec string, cmd func()) (EntryID, error) {
return c.AddJob(spec, FuncJob(cmd))
}
// AddJob adds a Job to the Cron to be run on the given schedule.
// The spec is parsed using the time zone of this Cron instance as the default.
// An opaque ID is returned that can be used to later remove it.
func (c *Cron) AddJob(spec string, cmd Job) (EntryID, error) {
schedule, err := c.parser.Parse(spec)
if err != nil {
return 0, err
}
return c.Schedule(schedule, cmd), nil
}
// Schedule adds a Job to the Cron to be run on the given schedule.
// The job is wrapped with the configured Chain.
func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
c.runningMu.Lock()
defer c.runningMu.Unlock()
c.nextID++
entry := &Entry{
ID: c.nextID,
Schedule: schedule,
WrappedJob: c.chain.Then(cmd),
Job: cmd,
}
if !c.running {
c.entries = append(c.entries, entry)
} else {
c.add <- entry
}
return entry.ID
}
// Entries returns a snapshot of the cron entries.
func (c *Cron) Entries() []Entry {
c.runningMu.Lock()
defer c.runningMu.Unlock()
if c.running {
replyChan := make(chan []Entry, 1)
c.snapshot <- replyChan
return <-replyChan
}
return c.entrySnapshot()
}
// Location gets the time zone location
func (c *Cron) Location() *time.Location {
return c.location
}
// Entry returns a snapshot of the given entry, or nil if it couldn't be found.
func (c *Cron) Entry(id EntryID) Entry {
for _, entry := range c.Entries() {
if id == entry.ID {
return entry
}
}
return Entry{}
}
// Remove an entry from being run in the future.
func (c *Cron) Remove(id EntryID) {
c.runningMu.Lock()
defer c.runningMu.Unlock()
if c.running {
c.remove <- id
} else {
c.removeEntry(id)
}
}
// Start the cron scheduler in its own goroutine, or no-op if already started.
func (c *Cron) Start() {
c.runningMu.Lock()
defer c.runningMu.Unlock()
if c.running {
return
}
c.running = true
go c.run()
}
// Run the cron scheduler, or no-op if already running.
func (c *Cron) Run() {
c.runningMu.Lock()
if c.running {
c.runningMu.Unlock()
return
}
c.running = true
c.runningMu.Unlock()
c.run()
}
// run the scheduler.. this is private just due to the need to synchronize
// access to the 'running' state variable.
func (c *Cron) run() {
c.logger.Info("start")
// Figure out the next activation times for each entry.
now := c.now()
for _, entry := range c.entries {
entry.Next = entry.Schedule.Next(now)
c.logger.Info("schedule", "now", now, "entry", entry.ID, "next", entry.Next)
}
for {
// Determine the next entry to run.
sort.Sort(byTime(c.entries))
var timer *time.Timer
if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
// If there are no entries yet, just sleep - it still handles new entries
// and stop requests.
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)
c.logger.Info("wake", "now", now)
// Run every entry whose next time was less than now
for _, e := range c.entries {
if e.Next.After(now) || e.Next.IsZero() {
break
}
c.startJob(e.WrappedJob)
e.Prev = e.Next
e.Next = e.Schedule.Next(now)
c.logger.Info("run", "now", now, "entry", e.ID, "next", e.Next)
}
case newEntry := <-c.add:
timer.Stop()
now = c.now()
newEntry.Next = newEntry.Schedule.Next(now)
c.entries = append(c.entries, newEntry)
c.logger.Info("added", "now", now, "entry", newEntry.ID, "next", newEntry.Next)
case replyChan := <-c.snapshot:
replyChan <- c.entrySnapshot()
continue
case <-c.stop:
timer.Stop()
c.logger.Info("stop")
return
case id := <-c.remove:
timer.Stop()
now = c.now()
c.removeEntry(id)
c.logger.Info("removed", "entry", id)
}
break
}
}
}
// startJob runs the given job in a new goroutine.
func (c *Cron) startJob(j Job) {
c.jobWaiter.Add(1)
go func() {
defer c.jobWaiter.Done()
j.Run()
}()
}
// now returns current time in c location
func (c *Cron) now() time.Time {
return time.Now().In(c.location)
}
// Stop stops the cron scheduler if it is running; otherwise it does nothing.
// A context is returned so the caller can wait for running jobs to complete.
func (c *Cron) Stop() context.Context {
c.runningMu.Lock()
defer c.runningMu.Unlock()
if c.running {
c.stop <- struct{}{}
c.running = false
}
ctx, cancel := context.WithCancel(context.Background())
go func() {
c.jobWaiter.Wait()
cancel()
}()
return ctx
}
// entrySnapshot returns a copy of the current cron entry list.
func (c *Cron) entrySnapshot() []Entry {
var entries = make([]Entry, len(c.entries))
for i, e := range c.entries {
entries[i] = *e
}
return entries
}
func (c *Cron) removeEntry(id EntryID) {
var entries []*Entry
for _, e := range c.entries {
if e.ID != id {
entries = append(entries, e)
}
}
c.entries = entries
}
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