125 lignes
2,6 Kio
Go
125 lignes
2,6 Kio
Go
package cache
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import (
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"container/list"
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"sync"
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"time"
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"github.com/ewhal/nyaa/common"
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"github.com/ewhal/nyaa/model"
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)
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var (
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cache = make(map[common.SearchParam]*list.Element, 10)
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ll = list.New()
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totalUsed int
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mu sync.Mutex
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// Mutable for quicker testing
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expiryTime = time.Second * 60
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// Size sets the maximum size of the cache before evicting unread data in MB
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Size float64 = 1 << 10
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)
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// Key stores the ID of either a thread or board page
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type Key struct {
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LastN uint8
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Board string
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ID uint64
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}
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// Single cache entry
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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
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data []model.Torrent
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size int
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}
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// Check the cache for and existing record. If miss, run fn to retrieve fresh
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// values.
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func Get(key common.SearchParam, fn func() ([]model.Torrent, error)) (
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[]model.Torrent, error,
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) {
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s := getStore(key)
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// Also keeps multiple requesters from simultaneously requesting the same
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// data
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s.Lock()
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defer s.Unlock()
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if s.isFresh() {
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return s.data, nil
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}
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data, err := fn()
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if err != nil {
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return nil, err
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}
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s.update(data)
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return data, nil
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}
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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()
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defer mu.Unlock()
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el := cache[k]
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if el == nil {
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s = &store{key: k}
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cache[k] = ll.PushFront(s)
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} else {
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ll.MoveToFront(el)
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s = el.Value.(*store)
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}
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return s
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}
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// Clear the cache. Only used for testing.
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func Clear() {
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mu.Lock()
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defer mu.Unlock()
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ll = list.New()
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cache = make(map[common.SearchParam]*list.Element, 10)
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}
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// Update the total used memory counter and evict, if over limit
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func updateUsedSize(delta int) {
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mu.Lock()
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defer mu.Unlock()
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totalUsed += delta
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for totalUsed > int(Size)*(1<<20) {
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s := ll.Remove(ll.Back()).(*store)
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delete(cache, s.key)
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totalUsed -= s.size
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}
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}
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// Return, if the data can still be considered fresh, without querying the DB
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func (s *store) isFresh() bool {
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return s.lastFetched.Add(expiryTime).Before(time.Now())
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}
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// Stores the new values of s. Calculates and stores the new size. Passes the
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// delta to the central cache to fire eviction checks.
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func (s *store) update(data []model.Torrent) {
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newSize := 0
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for _, d := range data {
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newSize += d.Size()
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}
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s.data = data
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delta := newSize - s.size
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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
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// already evicted, but that should never happen, unless you have a very
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// small cache, very large stored datasets and a lot of traffic.
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updateUsedSize(delta)
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}
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