TODO.md

@@ -29,6 +29,13 @@ P2: security: referer blacklist
 
 # Completed Steps
 
+- 2026-10-04 upstream host semaphores and variant `.meta` files no longer
+  outlive their use (closes #87): the fetcher counts the fetches holding or
+  waiting for a slot of each upstream host's semaphore and removes the host's
+  semaphore once none is left, so fetches from many hosts no longer leave one
+  semaphore each until restart; `VariantStorage.Delete` removes the variant's
+  `.meta` file along with it, a missing `.meta` file not being an error, and
+  `DeleteWithMeta`, which eviction called for that, is gone.
 - 2026-10-04 `README.md` matches the code (closes #74): "Storage" names the
   cache directories pixa uses (`cache/sources`, `cache/metadata`,
   `cache/variants`) and how files are named in each, and the comments in

internal/httpfetcher/fetch_internal_test.go

@@ -191,7 +191,15 @@ func fetchBody(t *testing.T, f *HTTPFetcher, path string) string {
 
 // semLen reports how many per-host semaphore slots are currently held.
 func semLen(f *HTTPFetcher, host string) int {
-	return len(f.getHostSemaphore(host))
+	f.hostSemMu.Lock()
+	defer f.hostSemMu.Unlock()
+
+	sem, ok := f.hostSems[host]
+	if !ok {
+		return 0
+	}
+
+	return len(sem.slots)
 }
 
 // hostSemCount reports how many hosts have a semaphore in hostSems.

internal/httpfetcher/httpfetcher.go

@@ -162,8 +162,11 @@ func DefaultConfig() *Config {
 type HTTPFetcher struct {
 	client *http.Client
 	config *Config
-	hostSems  map[string]chan struct{} // per-host semaphores
-	hostSemMu sync.Mutex               // protects hostSems map
+	// hostSems holds the semaphore of each host with a fetch holding or
+	// waiting for one of its slots; the entry is removed when the host's
+	// last such fetch gives its slot back or stops waiting.
+	hostSems  map[string]*hostSemaphore
+	hostSemMu sync.Mutex // protects hostSems and each entry's count
 	// allHostsSemaphore has one slot per connection allowed to all hosts
 	// together (config.MaxConnections).
 	allHostsSemaphore chan struct{}
@@ -171,6 +174,14 @@ type HTTPFetcher struct {
 	connectionWaitTimeout time.Duration
 }
 
+// hostSemaphore is one host's connection slots
+// (config.MaxConnectionsPerHost) and the number of fetches holding or
+// waiting for one of them.
+type hostSemaphore struct {
+	slots chan struct{}
+	count int
+}
+
 // New creates a new HTTPFetcher with SSRF protection.
 func New(config *Config) *HTTPFetcher {
 	if config == nil {
@@ -211,7 +222,7 @@ func New(config *Config) *HTTPFetcher {
 	return &HTTPFetcher{
 		client:                client,
 		config:                config,
-		hostSems:              make(map[string]chan struct{}),
+		hostSems:              make(map[string]*hostSemaphore),
 		allHostsSemaphore:     make(chan struct{}, config.MaxConnections),
 		connectionWaitTimeout: ConnectionWaitTimeout,
 	}
@@ -307,6 +318,8 @@ func (f *HTTPFetcher) acquireConnection(
 	select {
 	case hostSem <- struct{}{}:
 	case <-ctx.Done():
+		f.putHostSemaphore(host)
+
 		return nil, ctx.Err()
 	}
 
@@ -314,32 +327,55 @@ func (f *HTTPFetcher) acquireConnection(
 	case f.allHostsSemaphore <- struct{}{}:
 	case <-time.After(f.connectionWaitTimeout):
 		<-hostSem
+		f.putHostSemaphore(host)
 
 		return nil, ErrTooManyConnections
 	case <-ctx.Done():
 		<-hostSem
+		f.putHostSemaphore(host)
 
 		return nil, ctx.Err()
 	}
 
 	return func() {
 		<-hostSem
+		f.putHostSemaphore(host)
 		<-f.allHostsSemaphore
 	}, nil
 }
 
-// getHostSemaphore returns the semaphore for a host, creating it if necessary.
+// getHostSemaphore returns the semaphore for a host, creating it if
+// necessary, and counts the caller among the fetches using it. The caller
+// calls putHostSemaphore once it holds no slot and waits for none.
 func (f *HTTPFetcher) getHostSemaphore(host string) chan struct{} {
 	f.hostSemMu.Lock()
 	defer f.hostSemMu.Unlock()
 
 	sem, ok := f.hostSems[host]
 	if !ok {
-		sem = make(chan struct{}, f.config.MaxConnectionsPerHost)
+		sem = &hostSemaphore{
+			slots: make(chan struct{}, f.config.MaxConnectionsPerHost),
+		}
 		f.hostSems[host] = sem
 	}
 
-	return sem
+	sem.count++
+
+	return sem.slots
+}
+
+// putHostSemaphore stops counting the caller among the fetches using the
+// host's semaphore, and removes the semaphore when no fetch uses it.
+func (f *HTTPFetcher) putHostSemaphore(host string) {
+	f.hostSemMu.Lock()
+	defer f.hostSemMu.Unlock()
+
+	sem := f.hostSems[host]
+
+	sem.count--
+	if sem.count == 0 {
+		delete(f.hostSems, host)
+	}
 }
 
 // buildResult validates the upstream response and assembles a FetchResult

internal/imgcache/eviction.go

@@ -283,7 +283,7 @@ func (c *Cache) evictVariant(ctx context.Context, cacheKey VariantKey) error {
 
 	c.metaCache.Remove(cacheKey)
 
-	err = c.variants.DeleteWithMeta(cacheKey)
+	err = c.variants.Delete(cacheKey)
 	if err != nil {
 		return err
 	}

internal/imgcache/storage.go

@@ -564,7 +564,8 @@ func (s *VariantStorage) Exists(key VariantKey) bool {
 	return err == nil
 }
 
-// Delete removes content at the given key.
+// Delete removes the content at the given key together with its .meta
+// sidecar file. A missing file is not an error.
 func (s *VariantStorage) Delete(key VariantKey) error {
 	path := s.keyToPath(key)
 
@@ -573,18 +574,7 @@ func (s *VariantStorage) Delete(key VariantKey) error {
 		return fmt.Errorf("failed to delete content: %w", err)
 	}
 
-	return nil
-}
-
-// DeleteWithMeta removes the content at the given key together with
-// its .meta sidecar file. A missing file is not an error.
-func (s *VariantStorage) DeleteWithMeta(key VariantKey) error {
-	err := s.Delete(key)
-	if err != nil {
-		return err
-	}
-
-	metaPath := s.keyToPath(key) + ".meta"
+	metaPath := path + ".meta"
 
 	err = os.Remove(metaPath)
 	if err != nil && !os.IsNotExist(err) {