TODO.md

@@ -29,6 +29,14 @@ P2: security: referer blacklist
 
 # Completed Steps
 
+- 2026-10-04 shutdown stops cache eviction in progress (closes #102):
+  `StartEviction` runs the eviction goroutine with its own context, which
+  `StopEviction` cancels, so a pass in progress stops at its next database
+  call, file, row or eviction candidate instead of running to completion;
+  `StopEviction` takes a context and, when that context ends before the
+  goroutine exits, stops waiting and returns its error; the handlers' stop hook
+  passes fx's stop context, so an eviction still running when fx's stop
+  deadline ends fails the stop and makes the exit code 1.
 - 2026-10-04 dead code in `internal/imgcache` is gone (closes #73): `Purge`,
   which only returned an error and which nothing called, is no longer part of
   the `ImageCache` interface or `Service`; the `SignatureValidator`,

internal/handlers/handlers.go

@@ -58,23 +58,16 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 	}
 
 	lc.Append(fx.Hook{
-		// The eviction goroutine must outlive OnStart, so it cannot
-		// inherit this hook's context. It makes its own instead, which
-		// leaves it uncancellable: an in-flight pass runs to completion
-		// during OnStop regardless of the shutdown deadline. Making the
-		// loop cancellable changes shutdown semantics and is tracked
-		// separately in issue #102, rather than being folded into the
-		// lint-conformance change that surfaced it.
-		//nolint:contextcheck // see issue #102
+		//nolint:contextcheck // the eviction loop outlives OnStart; OnStop cancels it
 		OnStart: func(_ context.Context) error {
 			return s.initImageService()
 		},
-		OnStop: func(_ context.Context) error {
-			if s.imgCache != nil {
-				s.imgCache.StopEviction()
+		OnStop: func(ctx context.Context) error {
+			if s.imgCache == nil {
+				return nil
 			}
 
-			return nil
+			return s.imgCache.StopEviction(ctx)
 		},
 	})
 

internal/imgcache/cache.go

@@ -11,7 +11,6 @@ import (
 	"io"
 	"log/slog"
 	"path/filepath"
-	"sync"
 	"time"
 
 	lru "github.com/hashicorp/golang-lru/v2"
@@ -69,11 +68,11 @@ type Cache struct {
 
 	// Eviction machinery. The channels are created in NewCache so
 	// stores can signal write pressure without racing StartEviction.
+	// evictionCancel, set by StartEviction, cancels the eviction
+	// goroutine's context.
 	evictionPressure chan struct{}
-	evictionStop     chan struct{}
 	evictionDone     chan struct{}
-	evictionStarted  bool
-	evictionStopOnce sync.Once
+	evictionCancel   context.CancelFunc
 
 	// metaCache holds the content types of the variants most recently
 	// stored or served, so a hit does not read the variant's .meta file.
@@ -112,7 +111,6 @@ func NewCache(db *sql.DB, config CacheConfig) (*Cache, error) {
 		log:              log,
 		disabled:         config.DisableDiskCache,
 		evictionPressure: make(chan struct{}, 1),
-		evictionStop:     make(chan struct{}),
 		evictionDone:     make(chan struct{}),
 		metaCache:        metaCache,
 		contentLocks:     newContentLock(),

internal/imgcache/eviction.go

@@ -117,7 +117,8 @@ func (c *Cache) EvictToLimit(ctx context.Context) error {
 
 // evictBatch fetches one batch of LRU candidates across variants and
 // source blobs and evicts them oldest-first until excessBytes are
-// freed or the batch is exhausted. It returns the bytes freed.
+// freed or the batch is exhausted. It returns the bytes freed. Once ctx
+// is cancelled, it stops at the next candidate and returns ctx's error.
 func (c *Cache) evictBatch(ctx context.Context, excessBytes int64) (int64, error) {
 	candidates, err := c.evictionCandidates(ctx)
 	if err != nil {
@@ -131,6 +132,10 @@ func (c *Cache) evictBatch(ctx context.Context, excessBytes int64) (int64, error
 			break
 		}
 
+		if ctx.Err() != nil {
+			return freed, ctx.Err()
+		}
+
 		err := c.evictCandidate(ctx, candidate)
 		if err != nil {
 			c.log.Warn("failed to evict cache entry",
@@ -424,37 +429,44 @@ func (c *Cache) notifyWritePressure() {
 // startup and again on every periodic tick thereafter, and evicts to
 // the configured limit on the given periodic interval and on
 // write-pressure notifications. It is a no-op on a disabled cache or
-// when already started.
+// when already started. The goroutine outlives the caller, so it runs
+// with its own context, which StopEviction cancels.
 func (c *Cache) StartEviction(interval time.Duration) {
-	if c.disabled || c.evictionStarted {
+	if c.disabled || c.evictionCancel != nil {
 		return
 	}
 
-	c.evictionStarted = true
+	ctx, cancel := context.WithCancel(context.Background())
+	c.evictionCancel = cancel
 
-	go c.evictionLoop(interval)
+	go c.evictionLoop(ctx, interval)
 }
 
-// StopEviction stops the background eviction goroutine and waits for
-// it to exit. It is safe to call when eviction was never started, and
-// safe to call more than once.
-func (c *Cache) StopEviction() {
-	if !c.evictionStarted {
-		return
+// StopEviction cancels the background eviction goroutine, which
+// interrupts a pass in progress, and waits for it to exit or for ctx to
+// end, whichever comes first. In the second case it returns an error
+// wrapping ctx's error. It is safe to call when eviction was never
+// started, and safe to call more than once.
+func (c *Cache) StopEviction(ctx context.Context) error {
+	if c.evictionCancel == nil {
+		return nil
 	}
 
-	c.evictionStopOnce.Do(func() {
-		close(c.evictionStop)
-		<-c.evictionDone
-	})
+	c.evictionCancel()
+
+	select {
+	case <-c.evictionDone:
+		return nil
+	case <-ctx.Done():
+		return fmt.Errorf("cache eviction still running: %w", ctx.Err())
+	}
 }
 
-// evictionLoop is the body of the background eviction goroutine.
-func (c *Cache) evictionLoop(interval time.Duration) {
+// evictionLoop is the body of the background eviction goroutine. It
+// returns when ctx is cancelled.
+func (c *Cache) evictionLoop(ctx context.Context, interval time.Duration) {
 	defer close(c.evictionDone)
 
-	ctx := context.Background()
-
 	c.runReconciliationPass(ctx)
 	c.runEvictionPass(ctx)
 
@@ -463,7 +475,7 @@ func (c *Cache) evictionLoop(interval time.Duration) {
 
 	for {
 		select {
-		case <-c.evictionStop:
+		case <-ctx.Done():
 			return
 		case <-ticker.C:
 			// Reconciliation walks the cache directories, so it only
@@ -511,7 +523,8 @@ func (c *Cache) runReconciliationPass(ctx context.Context) {
 // know (and rows whose files are gone), and sweeps stale temp files
 // left behind by crashed writes. Running it periodically, not just
 // once, bounds how long such drift can accumulate unaccounted for on a
-// long-running process to one eviction interval.
+// long-running process to one eviction interval. Once ctx is cancelled,
+// it stops at the next file or row and returns ctx's error.
 func (c *Cache) reconcileAccounting(ctx context.Context) error {
 	if c.disabled {
 		return nil
@@ -546,6 +559,10 @@ func (c *Cache) reconcileVariantFiles(ctx context.Context) error {
 	return filepath.WalkDir(
 		c.variants.baseDir,
 		func(path string, entry fs.DirEntry, err error) error {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+
 			if err != nil || entry.IsDir() {
 				return err
 			}
@@ -634,6 +651,10 @@ func (c *Cache) reconcileVariantRows(ctx context.Context) error {
 	}
 
 	for _, key := range keys {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+
 		if c.variants.Exists(key) {
 			continue
 		}
@@ -699,6 +720,10 @@ func (c *Cache) reconcileSourceFiles(ctx context.Context) error {
 	return filepath.WalkDir(
 		c.srcContent.baseDir,
 		func(path string, entry fs.DirEntry, err error) error {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+
 			if err != nil || entry.IsDir() {
 				return err
 			}
@@ -760,6 +785,10 @@ func (c *Cache) reconcileSourceRows(ctx context.Context) error {
 	}
 
 	for _, hash := range hashes {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+
 		if c.srcContent.Exists(hash) {
 			continue
 		}

internal/imgcache/eviction_internal_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"database/sql"
+	"errors"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -657,7 +658,7 @@ func TestEvictionRunsUnderWritePressure(t *testing.T) {
 	// An interval far longer than the test ensures only write
 	// pressure can trigger eviction here.
 	cache.StartEviction(time.Hour)
-	defer cache.StopEviction()
+	defer func() { _ = cache.StopEviction(t.Context()) }()
 
 	keys := []VariantKey{
 		testVariantKeyOne, testVariantKeyTwo, testVariantKeyThree,
@@ -690,7 +691,7 @@ func TestEvictionRunsOnPeriodicSchedule(t *testing.T) {
 	// write-pressure notification fires and only the periodic ticker
 	// can trigger eviction.
 	cache.StartEviction(100 * time.Millisecond)
-	defer cache.StopEviction()
+	defer func() { _ = cache.StopEviction(t.Context()) }()
 
 	keys := []VariantKey{
 		testVariantKeyOne, testVariantKeyTwo, testVariantKeyThree,
@@ -751,7 +752,7 @@ func TestStartEvictionReconcilesAccountingWithDisk(t *testing.T) {
 	}
 
 	cache.StartEviction(time.Hour)
-	defer cache.StopEviction()
+	defer func() { _ = cache.StopEviction(t.Context()) }()
 
 	deadline := time.Now().Add(5 * time.Second)
 
@@ -808,7 +809,7 @@ func TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup(t *testing.T) {
 	const interval = 100 * time.Millisecond
 
 	cache.StartEviction(interval)
-	defer cache.StopEviction()
+	defer func() { _ = cache.StopEviction(t.Context()) }()
 
 	// Let startup reconciliation run and settle on an empty cache
 	// before introducing the untracked file, so the adoption we assert
@@ -862,6 +863,147 @@ func TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup(t *testing.T) {
 	}
 }
 
+// TestStopEvictionInterruptsPassInProgress holds the test database's
+// only connection, so the startup reconciliation pass waits for it, and
+// checks that StopEviction stops that pass instead of waiting for the
+// connection to come free.
+func TestStopEvictionInterruptsPassInProgress(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	conn, err := cache.db.Conn(t.Context())
+	if err != nil {
+		t.Fatalf("failed to take the database connection: %v", err)
+	}
+
+	defer func() { _ = conn.Close() }()
+
+	cache.StartEviction(time.Hour)
+
+	// The pass is in progress once it waits for the connection.
+	deadline := time.Now().Add(5 * time.Second)
+
+	for cache.db.Stats().WaitCount == 0 {
+		if time.Now().After(deadline) {
+			t.Fatal("the reconciliation pass never waited for the database")
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+
+	err = cache.StopEviction(ctx)
+	t.Logf("StopEviction() error = %v", err)
+
+	if err != nil {
+		t.Fatalf("StopEviction() error = %v, want nil: the pass waiting for "+
+			"the database did not stop", err)
+	}
+}
+
+// TestStopEvictionReturnsWhenItsContextEnds pauses an eviction pass where
+// cancellation cannot reach it, after a source blob's rows are deleted and
+// before its file is removed, and checks that StopEviction returns its
+// context's error when that context ends instead of waiting for the pass.
+// Once the pass goes on, the goroutine exits and no row points at a
+// missing file.
+func TestStopEvictionReturnsWhenItsContextEnds(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1)
+
+	paused := make(chan struct{})
+	resume := make(chan struct{})
+
+	cache.evictSourceBlobTestHook = func(ContentHash) {
+		close(paused)
+		<-resume
+	}
+
+	hash := storeEvictionTestSource(t, cache, "stop.example.com", "/a.jpg",
+		bytes.Repeat([]byte{0x61}, 1000))
+
+	cache.StartEviction(time.Hour)
+
+	select {
+	case <-paused:
+	case <-time.After(5 * time.Second):
+		t.Fatal("the eviction pass never reached the source blob")
+	}
+
+	ctx, cancel := context.WithTimeout(t.Context(), 50*time.Millisecond)
+	defer cancel()
+
+	err := cache.StopEviction(ctx)
+	t.Logf("StopEviction() error = %v", err)
+
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Errorf("StopEviction() error = %v, want context.DeadlineExceeded", err)
+	}
+
+	close(resume)
+
+	err = cache.StopEviction(t.Context())
+	if err != nil {
+		t.Fatalf("second StopEviction() error = %v, want nil", err)
+	}
+
+	assertNoDanglingReferences(t, cache)
+
+	if cache.srcContent.Exists(hash) {
+		t.Errorf("source blob %s is still on disk after its rows were deleted", hash)
+	}
+}
+
+// TestReconciliationWalksStopOnceCancelled checks that both directory
+// walks of a reconciliation pass return the context's error once it is
+// cancelled, leaving in place a stale temp file they would otherwise
+// remove.
+func TestReconciliationWalksStopOnceCancelled(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	ctx, cancel := context.WithCancel(t.Context())
+	cancel()
+
+	staleTime := time.Now().Add(-2 * staleTempFileAge)
+
+	walks := map[string]func(context.Context) error{
+		cache.variants.baseDir:   cache.reconcileVariantFiles,
+		cache.srcContent.baseDir: cache.reconcileSourceFiles,
+	}
+
+	for dir, walk := range walks {
+		tempFile := filepath.Join(dir, tempFilePrefix+"stale")
+
+		err := os.WriteFile(tempFile, []byte("partial"), 0o600)
+		if err != nil {
+			t.Fatalf("failed to write temp file: %v", err)
+		}
+
+		err = os.Chtimes(tempFile, staleTime, staleTime)
+		if err != nil {
+			t.Fatalf("failed to backdate temp file: %v", err)
+		}
+
+		err = walk(ctx)
+		t.Logf("walk of %s: error = %v", dir, err)
+
+		if !errors.Is(err, context.Canceled) {
+			t.Errorf("walk of %s: error = %v, want context.Canceled", dir, err)
+		}
+
+		_, err = os.Stat(tempFile)
+		if err != nil {
+			t.Errorf("walk of %s went on after cancellation: %v", dir, err)
+		}
+	}
+}
+
 // TestEvictSourceBlobExcludesConcurrentStoreOfIdenticalContent exercises
 // the exact TOCTOU window between evictSourceBlob's row-deletion
 // transaction commit and its content file unlink: a concurrent