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scheduler.go
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scheduler.go
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// Copyright 2019-present Open Networking Foundation.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package service
import (
"container/list"
"time"
)
// Scheduler provides deterministic scheduling for a state machine
type Scheduler interface {
// Execute executes a function asynchronously
Execute(f func())
// ScheduleOnce schedules a function to be run once after the given delay
ScheduleOnce(delay time.Duration, f func()) Timer
// ScheduleRepeat schedules a function to run repeatedly every interval starting after the given delay
ScheduleRepeat(delay time.Duration, interval time.Duration, f func()) Timer
// ScheduleIndex schedules a function to run at a specific index
ScheduleIndex(index uint64, f func())
}
// Timer is a cancellable timer
type Timer interface {
// Cancel cancels the timer, preventing it from running in the future
Cancel()
}
func newScheduler() *scheduler {
return &scheduler{
tasks: list.New(),
scheduledTasks: list.New(),
indexTasks: make(map[uint64]*list.List),
time: time.Now(),
}
}
type scheduler struct {
Scheduler
tasks *list.List
scheduledTasks *list.List
indexTasks map[uint64]*list.List
time time.Time
}
func (s *scheduler) Execute(f func()) {
s.tasks.PushBack(f)
}
func (s *scheduler) ScheduleOnce(delay time.Duration, f func()) Timer {
task := &task{
scheduler: s,
time: time.Now().Add(delay),
interval: 0,
callback: f,
}
s.schedule(task)
return task
}
func (s *scheduler) ScheduleRepeat(delay time.Duration, interval time.Duration, f func()) Timer {
task := &task{
scheduler: s,
time: time.Now().Add(delay),
interval: interval,
callback: f,
}
s.schedule(task)
return task
}
func (s *scheduler) ScheduleIndex(index uint64, f func()) {
tasks, ok := s.indexTasks[index]
if !ok {
tasks = list.New()
s.indexTasks[index] = tasks
}
tasks.PushBack(f)
}
// runImmediateTasks runs the immediate tasks in the scheduler queue
func (s *scheduler) runImmediateTasks() {
task := s.tasks.Front()
for task != nil {
task.Value.(func())()
task = task.Next()
}
s.tasks = list.New()
}
// runScheduleTasks runs the scheduled tasks in the scheduler queue
func (s *scheduler) runScheduledTasks(time time.Time) {
s.time = time
element := s.scheduledTasks.Front()
if element != nil {
complete := list.New()
for element != nil {
task := element.Value.(*task)
if task.isRunnable(time) {
next := element.Next()
s.scheduledTasks.Remove(element)
s.time = task.time
task.run()
complete.PushBack(task)
element = next
} else {
break
}
}
element = complete.Front()
for element != nil {
task := element.Value.(*task)
if task.interval > 0 {
task.time = s.time.Add(task.interval)
s.schedule(task)
}
element = element.Next()
}
}
}
// runIndex runs functions pending at the given index
func (s *scheduler) runIndex(index uint64) {
tasks, ok := s.indexTasks[index]
if ok {
task := tasks.Front()
for task != nil {
task.Value.(func())()
task = task.Next()
}
delete(s.indexTasks, index)
}
}
// schedule schedules a task
func (s *scheduler) schedule(t *task) {
if s.scheduledTasks.Len() == 0 {
t.element = s.scheduledTasks.PushBack(t)
} else {
element := s.scheduledTasks.Back()
for element != nil {
time := element.Value.(*task).time
if element.Value.(*task).time.UnixNano() < time.UnixNano() {
t.element = s.scheduledTasks.InsertAfter(t, element)
return
}
element = element.Prev()
}
t.element = s.scheduledTasks.PushFront(t)
}
}
// Scheduler task
type task struct {
Timer
scheduler *scheduler
interval time.Duration
callback func()
time time.Time
element *list.Element
}
func (t *task) isRunnable(time time.Time) bool {
return time.UnixNano() > t.time.UnixNano()
}
func (t *task) run() {
t.callback()
}
func (t *task) Cancel() {
if t.element != nil {
t.scheduler.scheduledTasks.Remove(t.element)
}
}