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package main
import (
"time"
"sync"
)
const (
addAction = 0
removeAction = 1
moveUpAction = 2
moveDownAction = 3
)
type Update struct {
Song *Song
Action uint
Timestamp int64
Next *Update
}
type Listener struct {
L chan bool
Next *Listener
}
var headUpdates map[int]*Update
var tailUpdates map[int]*Update
var listeners map[int]*Listener
var updateLock sync.Mutex
func init() {
headUpdates = make(map[int]*Update)
tailUpdates = make(map[int]*Update)
listeners = make(map[int]*Listener)
}
func addUpdate(pid int, action uint, song *Song) {
update := new(Update)
update.Song = song
update.Action = action
update.Timestamp = time.Nanoseconds()
updateLock.Lock()
defer updateLock.Unlock()
pup := tailUpdates[pid]
if pup != nil {
pup.Next = update
} else {
headUpdates[pid] = update
}
tailUpdates[pid] = update
listener := listeners[pid]
for listener != nil {
listener.L <- true
listener = listener.Next
}
listeners[pid] = nil
}
// assumes locked
func checkUpdates(pid int, timestamp int64) *Update {
pup, _ := headUpdates[pid]
for pup != nil {
if pup.Timestamp > timestamp {
return pup
}
pup = pup.Next
}
return nil
}
func getUpdates(id string, timestamp int64) *Update {
db := <-dbPool
pid := getpid(db, id)
dbPool <- db
if pid == -1 {
return nil
}
updateLock.Lock()
pup := checkUpdates(pid, timestamp)
if pup != nil {
updateLock.Unlock()
return pup
}
// didn't get updates
listener := new(Listener)
listener.L = make(chan bool)
lhead := listeners[pid]
if lhead != nil {
listener.Next = lhead
}
listeners[pid] = listener
updateLock.Unlock()
<-listener.L
updateLock.Lock()
pup = checkUpdates(pid, timestamp)
updateLock.Unlock()
return pup
}
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