Albirew/nyaa-pantsu
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nyaa-pantsu/cache/cache.go

129 lignes
2,7 Kio
Go
Brut Vue normale Historique

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package cache
import (
"container/list"
"sync"
"time"
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"github.com/ewhal/nyaa/common"
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"github.com/ewhal/nyaa/model"
)
const expiryTime = time.Minute
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var (
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cache = make(map[common.SearchParam]*list.Element, 10)
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ll = list.New()
totalUsed int
mu sync.Mutex
// Size sets the maximum size of the cache before evicting unread data in MB
Size float64 = 1 << 10
)
// Key stores the ID of either a thread or board page
type Key struct {
LastN uint8
Board string
ID uint64
}
// Single cache entry
type store struct {
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sync.Mutex // Controls general access to the contents of the struct
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lastFetched time.Time
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key common.SearchParam
data []model.Torrent
count, size int
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}
// Check the cache for and existing record. If miss, run fn to retrieve fresh
// values.
func Get(key common.SearchParam, fn func() ([]model.Torrent, int, error)) (
data []model.Torrent, count int, err error,
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) {
s := getStore(key)
// Also keeps multiple requesters from simultaneously requesting the same
// data
s.Lock()
defer s.Unlock()
if s.isFresh() {
return s.data, s.count, nil
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}
data, count, err = fn()
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if err != nil {
return
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}
s.update(data, count)
return
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}
// Retrieve a store from the cache or create a new one
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func getStore(k common.SearchParam) (s *store) {
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mu.Lock()
defer mu.Unlock()
el := cache[k]
if el == nil {
s = &store{key: k}
cache[k] = ll.PushFront(s)
} else {
ll.MoveToFront(el)
s = el.Value.(*store)
}
return s
}
// Clear the cache. Only used for testing.
func Clear() {
mu.Lock()
defer mu.Unlock()
ll = list.New()
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cache = make(map[common.SearchParam]*list.Element, 10)
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}
// Update the total used memory counter and evict, if over limit
func updateUsedSize(delta int) {
mu.Lock()
defer mu.Unlock()
totalUsed += delta
for totalUsed > int(Size)<<20 {
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s := ll.Remove(ll.Back()).(*store)
delete(cache, s.key)
totalUsed -= s.size
}
}
// Return, if the data can still be considered fresh, without querying the DB
func (s *store) isFresh() bool {
if s.lastFetched.IsZero() { // New store
return false
}
return s.lastFetched.Add(expiryTime).After(time.Now())
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}
// Stores the new values of s. Calculates and stores the new size. Passes the
// delta to the central cache to fire eviction checks.
func (s *store) update(data []model.Torrent, count int) {
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newSize := 0
for _, d := range data {
newSize += d.Size()
}
s.data = data
s.count = count
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delta := newSize - s.size
s.size = newSize
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s.lastFetched = time.Now()
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// Technically it is possible to update the size even when the store is
// already evicted, but that should never happen, unless you have a very
// small cache, very large stored datasets and a lot of traffic.
updateUsedSize(delta)
}