/
timewheel.go
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/
timewheel.go
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/*
Maddy Mail Server - Composable all-in-one email server.
Copyright © 2019-2020 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package queue
import (
"container/list"
"sync"
"sync/atomic"
"time"
)
type TimeSlot struct {
Time time.Time
Value interface{}
}
type TimeWheel struct {
stopped uint32
slots *list.List
slotsLock sync.Mutex
updateNotify chan time.Time
stopNotify chan struct{}
dispatch func(TimeSlot)
}
func NewTimeWheel(dispatch func(TimeSlot)) *TimeWheel {
tw := &TimeWheel{
slots: list.New(),
stopNotify: make(chan struct{}),
updateNotify: make(chan time.Time),
dispatch: dispatch,
}
go tw.tick()
return tw
}
func (tw *TimeWheel) Add(target time.Time, value interface{}) {
if atomic.LoadUint32(&tw.stopped) == 1 {
// Already stopped, ignore.
return
}
if value == nil {
panic("can't insert nil objects into TimeWheel queue")
}
tw.slotsLock.Lock()
tw.slots.PushBack(TimeSlot{Time: target, Value: value})
tw.slotsLock.Unlock()
tw.updateNotify <- target
}
func (tw *TimeWheel) Close() {
atomic.StoreUint32(&tw.stopped, 1)
// Idempotent Close is convenient sometimes.
if tw.stopNotify == nil {
return
}
tw.stopNotify <- struct{}{}
<-tw.stopNotify
tw.stopNotify = nil
close(tw.updateNotify)
}
func (tw *TimeWheel) tick() {
for {
now := time.Now()
// Look for list element closest to now.
tw.slotsLock.Lock()
var closestSlot TimeSlot
var closestEl *list.Element
for e := tw.slots.Front(); e != nil; e = e.Next() {
slot := e.Value.(TimeSlot)
if slot.Time.Sub(now) < closestSlot.Time.Sub(now) || closestSlot.Value == nil {
closestSlot = slot
closestEl = e
}
}
tw.slotsLock.Unlock()
// Only this goroutine removes elements from TimeWheel so we can be safe using closestSlot.
// Queue is empty. Just wait until update.
if closestEl == nil {
select {
case <-tw.updateNotify:
continue
case <-tw.stopNotify:
tw.stopNotify <- struct{}{}
return
}
}
timer := time.NewTimer(closestSlot.Time.Sub(now))
selectloop:
for {
select {
case <-timer.C:
tw.slotsLock.Lock()
tw.slots.Remove(closestEl)
tw.slotsLock.Unlock()
tw.dispatch(closestSlot)
break selectloop
case newTarget := <-tw.updateNotify:
// Avoid unnecessary restarts if new target is not going to affect our
// current wait time.
if closestSlot.Time.Sub(now) <= newTarget.Sub(now) {
continue
}
timer.Stop()
// Recalculate new slot time.
break selectloop
case <-tw.stopNotify:
tw.stopNotify <- struct{}{}
return
}
}
}
}