355 lines
8.6 KiB
Go
355 lines
8.6 KiB
Go
package cron
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import (
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"context"
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"sort"
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"sync"
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"time"
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)
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// Cron keeps track of any number of entries, invoking the associated func as
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// specified by the schedule. It may be started, stopped, and the entries may
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// be inspected while running.
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type Cron struct {
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entries []*Entry
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chain Chain
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stop chan struct{}
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add chan *Entry
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remove chan EntryID
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snapshot chan chan []Entry
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running bool
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logger Logger
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runningMu sync.Mutex
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location *time.Location
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parser ScheduleParser
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nextID EntryID
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jobWaiter sync.WaitGroup
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}
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// ScheduleParser is an interface for schedule spec parsers that return a Schedule
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type ScheduleParser interface {
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Parse(spec string) (Schedule, error)
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}
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// Job is an interface for submitted cron jobs.
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type Job interface {
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Run()
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}
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// Schedule describes a job's duty cycle.
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type Schedule interface {
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// Next returns the next activation time, later than the given time.
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// Next is invoked initially, and then each time the job is run.
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Next(time.Time) time.Time
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}
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// EntryID identifies an entry within a Cron instance
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type EntryID int
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// Entry consists of a schedule and the func to execute on that schedule.
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type Entry struct {
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// ID is the cron-assigned ID of this entry, which may be used to look up a
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// snapshot or remove it.
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ID EntryID
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// Schedule on which this job should be run.
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Schedule Schedule
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// Next time the job will run, or the zero time if Cron has not been
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// started or this entry's schedule is unsatisfiable
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Next time.Time
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// Prev is the last time this job was run, or the zero time if never.
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Prev time.Time
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// WrappedJob is the thing to run when the Schedule is activated.
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WrappedJob Job
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// Job is the thing that was submitted to cron.
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// It is kept around so that user code that needs to get at the job later,
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// e.g. via Entries() can do so.
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Job Job
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}
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// Valid returns true if this is not the zero entry.
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func (e Entry) Valid() bool { return e.ID != 0 }
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// byTime is a wrapper for sorting the entry array by time
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// (with zero time at the end).
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type byTime []*Entry
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func (s byTime) Len() int { return len(s) }
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func (s byTime) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
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func (s byTime) Less(i, j int) bool {
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// Two zero times should return false.
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// Otherwise, zero is "greater" than any other time.
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// (To sort it at the end of the list.)
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if s[i].Next.IsZero() {
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return false
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}
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if s[j].Next.IsZero() {
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return true
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}
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return s[i].Next.Before(s[j].Next)
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}
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// New returns a new Cron job runner, modified by the given options.
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//
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// Available Settings
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//
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// Time Zone
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// Description: The time zone in which schedules are interpreted
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// Default: time.Local
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//
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// Parser
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// Description: Parser converts cron spec strings into cron.Schedules.
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// Default: Accepts this spec: https://en.wikipedia.org/wiki/Cron
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//
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// Chain
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// Description: Wrap submitted jobs to customize behavior.
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// Default: A chain that recovers panics and logs them to stderr.
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//
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// See "cron.With*" to modify the default behavior.
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func New(opts ...Option) *Cron {
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c := &Cron{
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entries: nil,
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chain: NewChain(),
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add: make(chan *Entry),
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stop: make(chan struct{}),
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snapshot: make(chan chan []Entry),
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remove: make(chan EntryID),
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running: false,
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runningMu: sync.Mutex{},
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logger: DefaultLogger,
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location: time.Local,
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parser: standardParser,
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}
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for _, opt := range opts {
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opt(c)
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}
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return c
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}
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// FuncJob is a wrapper that turns a func() into a cron.Job
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type FuncJob func()
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func (f FuncJob) Run() { f() }
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// AddFunc adds a func to the Cron to be run on the given schedule.
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// The spec is parsed using the time zone of this Cron instance as the default.
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// An opaque ID is returned that can be used to later remove it.
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func (c *Cron) AddFunc(spec string, cmd func()) (EntryID, error) {
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return c.AddJob(spec, FuncJob(cmd))
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}
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// AddJob adds a Job to the Cron to be run on the given schedule.
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// The spec is parsed using the time zone of this Cron instance as the default.
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// An opaque ID is returned that can be used to later remove it.
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func (c *Cron) AddJob(spec string, cmd Job) (EntryID, error) {
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schedule, err := c.parser.Parse(spec)
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if err != nil {
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return 0, err
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}
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return c.Schedule(schedule, cmd), nil
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}
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// Schedule adds a Job to the Cron to be run on the given schedule.
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// The job is wrapped with the configured Chain.
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func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
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c.runningMu.Lock()
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defer c.runningMu.Unlock()
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c.nextID++
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entry := &Entry{
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ID: c.nextID,
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Schedule: schedule,
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WrappedJob: c.chain.Then(cmd),
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Job: cmd,
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}
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if !c.running {
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c.entries = append(c.entries, entry)
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} else {
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c.add <- entry
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}
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return entry.ID
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}
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// Entries returns a snapshot of the cron entries.
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func (c *Cron) Entries() []Entry {
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c.runningMu.Lock()
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defer c.runningMu.Unlock()
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if c.running {
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replyChan := make(chan []Entry, 1)
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c.snapshot <- replyChan
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return <-replyChan
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}
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return c.entrySnapshot()
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}
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// Location gets the time zone location
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func (c *Cron) Location() *time.Location {
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return c.location
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}
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// Entry returns a snapshot of the given entry, or nil if it couldn't be found.
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func (c *Cron) Entry(id EntryID) Entry {
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for _, entry := range c.Entries() {
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if id == entry.ID {
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return entry
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}
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}
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return Entry{}
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}
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// Remove an entry from being run in the future.
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func (c *Cron) Remove(id EntryID) {
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c.runningMu.Lock()
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defer c.runningMu.Unlock()
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if c.running {
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c.remove <- id
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} else {
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c.removeEntry(id)
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}
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}
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// Start the cron scheduler in its own goroutine, or no-op if already started.
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func (c *Cron) Start() {
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c.runningMu.Lock()
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defer c.runningMu.Unlock()
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if c.running {
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return
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}
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c.running = true
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go c.run()
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}
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// Run the cron scheduler, or no-op if already running.
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func (c *Cron) Run() {
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c.runningMu.Lock()
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if c.running {
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c.runningMu.Unlock()
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return
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}
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c.running = true
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c.runningMu.Unlock()
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c.run()
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}
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// run the scheduler.. this is private just due to the need to synchronize
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// access to the 'running' state variable.
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func (c *Cron) run() {
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c.logger.Info("start")
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// Figure out the next activation times for each entry.
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now := c.now()
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for _, entry := range c.entries {
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entry.Next = entry.Schedule.Next(now)
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c.logger.Info("schedule", "now", now, "entry", entry.ID, "next", entry.Next)
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}
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for {
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// Determine the next entry to run.
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sort.Sort(byTime(c.entries))
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var timer *time.Timer
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if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
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// If there are no entries yet, just sleep - it still handles new entries
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// and stop requests.
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timer = time.NewTimer(100000 * time.Hour)
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} else {
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timer = time.NewTimer(c.entries[0].Next.Sub(now))
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}
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for {
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select {
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case now = <-timer.C:
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now = now.In(c.location)
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c.logger.Info("wake", "now", now)
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// Run every entry whose next time was less than now
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for _, e := range c.entries {
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if e.Next.After(now) || e.Next.IsZero() {
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break
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}
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c.startJob(e.WrappedJob)
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e.Prev = e.Next
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e.Next = e.Schedule.Next(now)
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c.logger.Info("run", "now", now, "entry", e.ID, "next", e.Next)
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}
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case newEntry := <-c.add:
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timer.Stop()
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now = c.now()
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newEntry.Next = newEntry.Schedule.Next(now)
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c.entries = append(c.entries, newEntry)
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c.logger.Info("added", "now", now, "entry", newEntry.ID, "next", newEntry.Next)
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case replyChan := <-c.snapshot:
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replyChan <- c.entrySnapshot()
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continue
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case <-c.stop:
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timer.Stop()
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c.logger.Info("stop")
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return
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case id := <-c.remove:
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timer.Stop()
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now = c.now()
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c.removeEntry(id)
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c.logger.Info("removed", "entry", id)
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}
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break
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}
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}
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}
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// startJob runs the given job in a new goroutine.
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func (c *Cron) startJob(j Job) {
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c.jobWaiter.Add(1)
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go func() {
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defer c.jobWaiter.Done()
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j.Run()
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}()
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}
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// now returns current time in c location
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func (c *Cron) now() time.Time {
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return time.Now().In(c.location)
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}
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// Stop stops the cron scheduler if it is running; otherwise it does nothing.
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// A context is returned so the caller can wait for running jobs to complete.
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func (c *Cron) Stop() context.Context {
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c.runningMu.Lock()
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defer c.runningMu.Unlock()
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if c.running {
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c.stop <- struct{}{}
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c.running = false
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}
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ctx, cancel := context.WithCancel(context.Background())
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go func() {
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c.jobWaiter.Wait()
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cancel()
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}()
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return ctx
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}
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// entrySnapshot returns a copy of the current cron entry list.
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func (c *Cron) entrySnapshot() []Entry {
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var entries = make([]Entry, len(c.entries))
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for i, e := range c.entries {
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entries[i] = *e
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}
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return entries
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}
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func (c *Cron) removeEntry(id EntryID) {
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var entries []*Entry
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for _, e := range c.entries {
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if e.ID != id {
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entries = append(entries, e)
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}
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}
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c.entries = entries
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}
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