perf: cache generated image thumbnails

internal/api/thumbnail_cache_test.go

@@ -0,0 +1,72 @@
+package api
+
+import (
+	"errors"
+	"sync"
+	"sync/atomic"
+	"testing"
+)
+
+func TestThumbnailCacheDeduplicatesConcurrentBuilds(t *testing.T) {
+	c := newThumbnailCache()
+	key := thumbnailCacheKey{Path: "photo.jpg", Size: 10, ModTime: 20}
+	var builds atomic.Int32
+	const workers = 24
+	var wg sync.WaitGroup
+	results := make([][]byte, workers)
+	errs := make([]error, workers)
+	wg.Add(workers)
+	for i := 0; i < workers; i++ {
+		go func(i int) {
+			defer wg.Done()
+			results[i], errs[i] = c.Do(key, func() ([]byte, error) {
+				builds.Add(1)
+				return []byte("thumbnail"), nil
+			})
+		}(i)
+	}
+	wg.Wait()
+	if builds.Load() != 1 {
+		t.Fatalf("thumbnail builder ran %d times, want 1", builds.Load())
+	}
+	for i := range results {
+		if errs[i] != nil || string(results[i]) != "thumbnail" {
+			t.Fatalf("worker %d got result %q, err=%v", i, results[i], errs[i])
+		}
+	}
+}
+
+func TestThumbnailCacheDoesNotCacheErrors(t *testing.T) {
+	c := newThumbnailCache()
+	key := thumbnailCacheKey{Path: "broken.jpg"}
+	wantErr := errors.New("decode failed")
+	var builds atomic.Int32
+	for i := 0; i < 2; i++ {
+		_, err := c.Do(key, func() ([]byte, error) {
+			builds.Add(1)
+			return nil, wantErr
+		})
+		if !errors.Is(err, wantErr) {
+			t.Fatalf("got err %v, want %v", err, wantErr)
+		}
+	}
+	if builds.Load() != 2 {
+		t.Fatalf("error result was cached; builder ran %d times", builds.Load())
+	}
+}
+
+func TestThumbnailCacheEvictsByBound(t *testing.T) {
+	c := newThumbnailCache()
+	c.maxItems = 2
+	for i := 0; i < 3; i++ {
+		key := thumbnailCacheKey{Path: string(rune('a' + i))}
+		if _, err := c.Do(key, func() ([]byte, error) { return []byte("x"), nil }); err != nil {
+			t.Fatal(err)
+		}
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if len(c.items) != 2 || c.order.Len() != 2 {
+		t.Fatalf("cache size=%d/list=%d, want 2/2", len(c.items), c.order.Len())
+	}
+}