add cleanup task to widget pool

ui/util/widgetpool.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"sync"
 	"time"
 
 	"fyne.io/fyne/v2"
@@ -19,11 +20,16 @@ const (
 	numWidgetTypes
 )
 
+const (
+	multipleItemsExpiry = 2 * time.Minute
+	singleItemExpiry    = 5 * time.Minute
+)
+
 // A pool to share commonly-used widgets across pages to reduce
 // creation of new widgets and memory allocations.
-// It is not thread-safe, which is fine for its current use.
 type WidgetPool struct {
-	pool [][]pooledWidget
+	mut   sync.Mutex
+	pools [][]pooledWidget
 }
 
 type pooledWidget struct {
@@ -31,21 +37,30 @@ type pooledWidget struct {
 	releasedAt int64 // unixMillis
 }
 
-func NewWidgetPool() WidgetPool {
-	return WidgetPool{
-		pool: make([][]pooledWidget, numWidgetTypes),
+func NewWidgetPool() *WidgetPool {
+	p := &WidgetPool{
+		pools: make([][]pooledWidget, numWidgetTypes),
 	}
+	go func() {
+		t := time.NewTicker(2 * time.Minute)
+		for range t.C {
+			p.cleanUpExpiredItems()
+		}
+	}()
+	return p
 }
 
 // Obtain obtains a widget of the given type from the pool, if one exists.
 // Returns nil if there is no available widget.
 func (w *WidgetPool) Obtain(typ WidgetType) fyne.CanvasObject {
+	w.mut.Lock()
+	defer w.mut.Unlock()
 	var widget fyne.CanvasObject
-	if l := len(w.pool[typ]); l > 0 {
+	if l := len(w.pools[typ]); l > 0 {
 		i := l - 1
-		widget = w.pool[typ][i].widget
-		w.pool[typ][i].widget = nil
-		w.pool[typ] = w.pool[typ][:i]
+		widget = w.pools[typ][i].widget
+		w.pools[typ][i].widget = nil
+		w.pools[typ] = w.pools[typ][:i]
 	}
 	return widget
 }
@@ -54,8 +69,31 @@ func (w *WidgetPool) Obtain(typ WidgetType) fyne.CanvasObject {
 // The widget must not be modified by the releaser after release,
 // since it may be Obtained for a new use at any time.
 func (w *WidgetPool) Release(typ WidgetType, wid fyne.CanvasObject) {
-	w.pool[typ] = append(w.pool[typ], pooledWidget{
+	w.mut.Lock()
+	defer w.mut.Unlock()
+	w.pools[typ] = append(w.pools[typ], pooledWidget{
 		widget:     wid,
 		releasedAt: time.Now().UnixMilli(),
 	})
 }
+
+func (w *WidgetPool) cleanUpExpiredItems() {
+	w.mut.Lock()
+	defer w.mut.Unlock()
+	for widTyp, pool := range w.pools {
+		newP := make([]pooledWidget, 0, len(pool))
+		l := len(pool)
+		for _, wid := range pool {
+			timeSinceRelease := time.Since(time.UnixMilli(wid.releasedAt))
+			if l > 1 && timeSinceRelease > multipleItemsExpiry {
+				l-- // let expire if >1 item in pool and released long enough ago
+			} else if l == 1 && timeSinceRelease > singleItemExpiry {
+				l-- // let expire if last item in pool and released long enough ago
+			} else {
+				newP = append(newP, wid) // not expired
+			}
+		}
+		// re-assign non-expired items back to this widget type pool
+		w.pools[widTyp] = newP
+	}
+}