remove gcache dependency, switch to custom image cache with TTL for memory savings

backend/albumiterator.go

@@ -4,7 +4,6 @@ import (
 	"log"
 	"strconv"
 
-	"github.com/bluele/gcache"
 	subsonic "github.com/dweymouth/go-subsonic"
 )
 
@@ -15,15 +14,12 @@ type AlbumIterator interface {
 type LibraryManager struct {
 	PreCacheCoverFn func(string)
 
-	s                *ServerManager
+	s *ServerManager
-	albumDetailCache gcache.Cache
 }
 
 func NewLibraryManager(s *ServerManager) *LibraryManager {
-	cache := gcache.New(250).LRU().Build()
 	return &LibraryManager{
-		s:                s,
+		s: s,
-		albumDetailCache: cache,
 	}
 }
 
@@ -85,21 +81,11 @@ func (l *LibraryManager) SearchIterWithFilter(query string, filter func(*subsoni
 	return l.newSearchIter(query, filter)
 }
 
-func (l *LibraryManager) CacheAlbum(a *subsonic.AlbumID3) {
-	l.albumDetailCache.Set(a.ID, a)
-}
-
 func (l *LibraryManager) GetAlbum(id string) (*subsonic.AlbumID3, error) {
-	if l.albumDetailCache.Has(id) {
-		if a, err := l.albumDetailCache.Get(id); err == nil {
-			return a.(*subsonic.AlbumID3), nil
-		}
-	}
 	a, err := l.s.Server.GetAlbum(id)
 	if err != nil {
 		return nil, err
 	}
-	l.albumDetailCache.Set(a.ID, a)
 	return a, nil
 }
 

backend/app.go

@@ -50,7 +50,7 @@ func StartupApp() (*App, error) {
 	a.ServerManager = NewServerManager()
 	a.PlaybackManager = NewPlaybackManager(a.bgrndCtx, a.ServerManager, a.Player)
 	a.LibraryManager = NewLibraryManager(a.ServerManager)
-	a.ImageManager = NewImageManager(a.ServerManager, configdir.LocalCache(AppName))
+	a.ImageManager = NewImageManager(a.bgrndCtx, a.ServerManager, configdir.LocalCache(AppName))
 	a.LibraryManager.PreCacheCoverFn = func(albumID string) {
 		_, _ = a.ImageManager.GetAlbumThumbnail(albumID)
 	}

backend/imagecache.go

@@ -1,6 +1,7 @@
 package backend
 
 import (
+	"container/heap"
 	"context"
 	"errors"
 	"image"
@@ -17,7 +18,7 @@ type CacheItem struct {
 	lastAccessed int64
 }
 
-// A custom cache for images with the following eviction strategy:
+// A custom in-memory cache for images with the following eviction strategy:
 //  1. If there are fewer than MinSize items in the cache, none will be evicted
 //  2. If a new addition would make the cache exceed MaxSize, an item will be immediately evicted
 //     2a. in this case, evict the LRU expired item or if none expired, the LRU item
@@ -36,12 +37,13 @@ var (
 	ErrNotFound = errors.New("item not found")
 )
 
-func (i *ImageCache) Init(ctx context.Context) {
+func (i *ImageCache) Init(ctx context.Context, evictionInterval time.Duration) {
 	i.cache = make(map[string]CacheItem)
+	go i.periodicallyEvict(ctx, evictionInterval)
 }
 
 // holds writer lock for O(i.MaxSize) worst case
-func (i *ImageCache) AddWithTTL(key string, val image.Image, ttl time.Duration) {
+func (i *ImageCache) SetWithTTL(key string, val image.Image, ttl time.Duration) {
 	i.mu.Lock()
 	defer i.mu.Unlock()
 
@@ -54,17 +56,17 @@ func (i *ImageCache) AddWithTTL(key string, val image.Image, ttl time.Duration)
 	}
 	if len(i.cache) == i.MaxSize {
 		i.evictOne()
-		i.cache[key] = CacheItem{
+	}
-			val:          val,
+	i.cache[key] = CacheItem{
-			ttl:          ttl,
+		val:          val,
-			expiresAt:    time.Now().Add(ttl).Unix(),
+		ttl:          ttl,
-			lastAccessed: time.Now().Unix(),
+		expiresAt:    time.Now().Add(ttl).Unix(),
-		}
+		lastAccessed: time.Now().Unix(),
 	}
 }
 
-func (i *ImageCache) Add(key string, val image.Image) {
+func (i *ImageCache) Set(key string, val image.Image) {
-	i.AddWithTTL(key, val, i.DefaultTTL)
+	i.SetWithTTL(key, val, i.DefaultTTL)
 }
 
 func (i *ImageCache) Has(key string) bool {
@@ -75,7 +77,11 @@ func (i *ImageCache) Has(key string) bool {
 	return ok
 }
 
-func (i *ImageCache) Get(key string, resetTTL bool) (image.Image, error) {
+func (i *ImageCache) Get(key string) (image.Image, error) {
+	return i.GetResetTTL(key, false)
+}
+
+func (i *ImageCache) GetResetTTL(key string, resetTTL bool) (image.Image, error) {
 	i.mu.RLock()
 	defer i.mu.RUnlock()
 
@@ -128,15 +134,56 @@ func (i *ImageCache) evictOne() {
 	}
 }
 
+func (i *ImageCache) periodicallyEvict(ctx context.Context, interval time.Duration) {
+	t := time.NewTicker(interval)
+	for {
+		select {
+		case <-ctx.Done():
+			t.Stop()
+			return
+		case <-t.C:
+			i.EvictExpired()
+		}
+	}
+}
+
 type expiredItem struct {
 	key          string
 	lastAccessed int64
 }
 
-// TODO
+type expiredHeap []expiredItem
+
+func (h expiredHeap) Len() int           { return len(h) }
+func (h expiredHeap) Less(i, j int) bool { return h[i].lastAccessed < h[j].lastAccessed }
+func (h expiredHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *expiredHeap) Push(x any) {
+	// Push and Pop use pointer receivers because they modify the slice's length,
+	// not just its contents.
+	*h = append(*h, x.(expiredItem))
+}
+
+func (h *expiredHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+// EvictExpired evicts least recently used expired items from the cache
+// until there are no more expired items or the cache contains MinSize elements
+// Holds the reader lock for O(n) time and writer lock for O(n)
 func (i *ImageCache) EvictExpired() {
 	i.mu.RLock()
-	expired := make([]expiredItem, 0, len(i.cache)-i.MinSize)
+	count := len(i.cache)
+	sliceCap := count - i.MinSize
+	if sliceCap <= 0 {
+		i.mu.RUnlock()
+		return
+	}
+	expired := make(expiredHeap, 0, sliceCap)
 	now := time.Now().Unix()
 	for k, v := range i.cache {
 		if v.expiresAt < now {
@@ -145,16 +192,21 @@ func (i *ImageCache) EvictExpired() {
 	}
 	i.mu.RUnlock()
 
-	count := len(i.cache)
+	heap.Init(&expired)
-	for count > i.MinSize {
+	var keysToRemove []string
+	for count > i.MinSize && len(expired) > 0 {
+		keysToRemove = append(keysToRemove, heap.Pop(&expired).(expiredItem).key)
+		count -= 1
+	}
 
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	for _, key := range keysToRemove {
+		// during the interim when we don't hold the lock, some expired items
+		// could have been re-set, so check expiry again
+		if item, ok := i.cache[key]; ok && item.expiresAt < now {
+			delete(i.cache, key)
+		}
 	}
 
 }
-
-func heapify(arr *[]expiredItem, i int) {
-	//smallest := i
-	//lChild := 2*i + 1
-	//rChild := 2*i + 2
-
-}

backend/imagemanager.go

@@ -1,6 +1,7 @@
 package backend
 
 import (
+	"context"
 	"fmt"
 	"image"
 	"image/jpeg"
@@ -11,62 +12,55 @@ import (
 	"time"
 
 	"github.com/20after4/configdir"
-	"github.com/bluele/gcache"
 )
 
 type ImageManager struct {
 	s              *ServerManager
 	baseCacheDir   string
-	thumbnailCache gcache.Cache
+	thumbnailCache ImageCache
 
 	cachedFullSizeCover   image.Image
 	cachedFullSizeCoverID string
 }
 
-func NewImageManager(s *ServerManager, baseCacheDir string) *ImageManager {
+func NewImageManager(ctx context.Context, s *ServerManager, baseCacheDir string) *ImageManager {
-	cache := gcache.New(100).LRU().Build()
 	if err := configdir.MakePath(baseCacheDir); err != nil {
 		log.Println("failed to create album cover cache dir")
 		baseCacheDir = ""
 	}
-	return &ImageManager{
+	i := &ImageManager{
-		s:              s,
+		s:            s,
-		baseCacheDir:   baseCacheDir,
+		baseCacheDir: baseCacheDir,
-		thumbnailCache: cache,
+		thumbnailCache: ImageCache{
+			MinSize:    24,
+			MaxSize:    150,
+			DefaultTTL: 1 * time.Minute,
+		},
 	}
+	i.thumbnailCache.Init(ctx, 2*time.Minute)
+	return i
 }
 
 func (i *ImageManager) GetAlbumThumbnailFromCache(albumID string) (image.Image, bool) {
-	if img, err := i.thumbnailCache.Get(albumID); err == nil && img != nil {
+	if img, err := i.thumbnailCache.GetResetTTL(albumID, true); err == nil && img != nil {
-		return img.(image.Image), true
+		return img, true
 	}
 	return nil, false
 }
 
 func (i *ImageManager) GetAlbumThumbnail(albumID string) (image.Image, error) {
+	if im, ok := i.GetAlbumThumbnailFromCache(albumID); ok {
+		return im, nil
+	}
+	return i.fetchAndCacheCoverFromDiskOrServer(albumID, i.thumbnailCache.DefaultTTL)
+}
+
+func (i *ImageManager) GetAlbumThumbnailWithTTL(albumID string, ttl time.Duration) (image.Image, error) {
 	// in-memory cache
-	if i.thumbnailCache.Has(albumID) {
+	if img, err := i.thumbnailCache.GetWithNewTTL(albumID, ttl); err == nil {
-		if img, err := i.thumbnailCache.Get(albumID); err == nil {
+		return img, nil
-			return img.(image.Image), nil
-		}
 	}
-
+	return i.fetchAndCacheCoverFromDiskOrServer(albumID, ttl)
-	// on disc cache
-	path := i.filePathForCover(albumID)
-	if i.ensureCoverCacheDir() != "" {
-		if s, err := os.Stat(path); err == nil {
-			go i.checkRefreshLocalCover(s, albumID)
-			if f, err := os.Open(path); err == nil {
-				defer f.Close()
-				if img, _, err := image.Decode(f); err == nil {
-					i.thumbnailCache.Set(albumID, img)
-					return img, nil
-				}
-			}
-		}
-	}
-
-	return i.fetchAndCacheCoverFromServer(albumID)
 }
 
 func (i *ImageManager) GetFullSizeAlbumCover(albumID string) (image.Image, error) {
@@ -88,7 +82,26 @@ func (i *ImageManager) ensureCoverCacheDir() string {
 	return path
 }
 
-func (i *ImageManager) fetchAndCacheCoverFromServer(albumID string) (image.Image, error) {
+func (i *ImageManager) fetchAndCacheCoverFromDiskOrServer(albumID string, ttl time.Duration) (image.Image, error) {
+	// on disc cache
+	path := i.filePathForCover(albumID)
+	if i.ensureCoverCacheDir() != "" {
+		if s, err := os.Stat(path); err == nil {
+			go i.checkRefreshLocalCover(s, albumID)
+			if f, err := os.Open(path); err == nil {
+				defer f.Close()
+				if img, _, err := image.Decode(f); err == nil {
+					i.thumbnailCache.SetWithTTL(albumID, img, ttl)
+					return img, nil
+				}
+			}
+		}
+	}
+
+	return i.fetchAndCacheCoverFromServer(albumID, ttl)
+}
+
+func (i *ImageManager) fetchAndCacheCoverFromServer(albumID string, ttl time.Duration) (image.Image, error) {
 	img, err := i.s.Server.GetCoverArt(albumID, map[string]string{"size": "300"})
 	if err != nil {
 		return nil, err
@@ -107,8 +120,8 @@ func (i *ImageManager) fetchAndCacheCoverFromServer(albumID string) (image.Image
 }
 
 func (i *ImageManager) checkRefreshLocalCover(stat os.FileInfo, albumID string) {
-	if time.Now().Sub(stat.ModTime()) > 24*time.Hour {
+	if time.Since(stat.ModTime()) > 24*time.Hour {
-		i.fetchAndCacheCoverFromServer(albumID)
+		i.fetchAndCacheCoverFromServer(albumID, i.thumbnailCache.DefaultTTL)
 	}
 }
 

go.mod

@@ -5,7 +5,6 @@ go 1.19
 require (
 	fyne.io/fyne/v2 v2.2.4
 	github.com/20after4/configdir v0.1.1
-	github.com/bluele/gcache v0.0.2
 	github.com/dweymouth/go-subsonic v0.0.0-20221214005741-bd8048fa1863
 	github.com/google/uuid v1.3.0
 	github.com/pelletier/go-toml v1.9.3

go.sum

@@ -53,8 +53,6 @@ github.com/armon/go-metrics v0.0.0-20180917152333-f0300d1749da/go.mod h1:Q73ZrmV
 github.com/armon/go-radix v0.0.0-20180808171621-7fddfc383310/go.mod h1:ufUuZ+zHj4x4TnLV4JWEpy2hxWSpsRywHrMgIH9cCH8=
 github.com/bgentry/speakeasy v0.1.0/go.mod h1:+zsyZBPWlz7T6j88CTgSN5bM796AkVf0kBD4zp0CCIs=
 github.com/bketelsen/crypt v0.0.4/go.mod h1:aI6NrJ0pMGgvZKL1iVgXLnfIFJtfV+bKCoqOes/6LfM=
-github.com/bluele/gcache v0.0.2 h1:WcbfdXICg7G/DGBh1PFfcirkWOQV+v077yF1pSy3DGw=
-github.com/bluele/gcache v0.0.2/go.mod h1:m15KV+ECjptwSPxKhOhQoAFQVtUFjTVkc3H8o0t/fp0=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
 github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=

ui/bottompanel.go

@@ -8,6 +8,7 @@ import (
 	"supersonic/ui/browsing"
 	"supersonic/ui/layouts"
 	"supersonic/ui/widgets"
+	"time"
 
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/container"
@@ -89,7 +90,12 @@ func (bp *BottomPanel) onSongChange(song *subsonic.Child) {
 	} else {
 		var im image.Image
 		if bp.ImageManager != nil {
-			im, _ = bp.ImageManager.GetAlbumThumbnail(song.AlbumID)
+			// set image to expire not long after the length of the song
+			// if song is played through without much pausing, image will still
+			// be in cache for the next song if it's from the same album, or
+			// if the user navigates to the album page for the track
+			imgTTLSec := song.Duration + 30
+			im, _ = bp.ImageManager.GetAlbumThumbnailWithTTL(song.AlbumID, time.Duration(imgTTLSec)*time.Second)
 		}
 		bp.NowPlaying.Update(song.Title, song.Artist, song.Album, im)
 	}