Scope writer locks to each writer.

Signed-off-by: Niklas Gehlen <niklas@namespacelabs.com>

plugins/content/local/locks.go

@@ -18,7 +18,6 @@ package local
 
 import (
 	"fmt"
-	"sync"
 	"time"
 
 	"github.com/containerd/errdefs"
@@ -30,17 +29,11 @@ type lock struct {
 	since time.Time
 }
 
-var (
-	// locks lets us lock in process
-	locks   = make(map[string]*lock)
-	locksMu sync.Mutex
-)
+func (s *store) tryLock(ref string) error {
+	s.locksMu.Lock()
+	defer s.locksMu.Unlock()
 
-func tryLock(ref string) error {
-	locksMu.Lock()
-	defer locksMu.Unlock()
-
-	if v, ok := locks[ref]; ok {
+	if v, ok := s.locks[ref]; ok {
 		// Returning the duration may help developers distinguish dead locks (long duration) from
 		// lock contentions (short duration).
 		now := time.Now()
@@ -50,13 +43,13 @@ func tryLock(ref string) error {
 		)
 	}
 
-	locks[ref] = &lock{time.Now()}
+	s.locks[ref] = &lock{time.Now()}
 	return nil
 }
 
-func unlock(ref string) {
-	locksMu.Lock()
-	defer locksMu.Unlock()
+func (s *store) unlock(ref string) {
+	s.locksMu.Lock()
+	defer s.locksMu.Unlock()
 
-	delete(locks, ref)
+	delete(s.locks, ref)
 }

plugins/content/local/locks_test.go

@@ -24,11 +24,13 @@ import (
 )
 
 func TestTryLock(t *testing.T) {
-	err := tryLock("testref")
-	assert.NoError(t, err)
-	defer unlock("testref")
+	s := &store{locks: map[string]*lock{}}
 
-	err = tryLock("testref")
+	err := s.tryLock("testref")
+	assert.NoError(t, err)
+	defer s.unlock("testref")
+
+	err = s.tryLock("testref")
 	require.NotNil(t, err)
 	assert.Contains(t, err.Error(), "ref testref locked for ")
 }

plugins/content/local/store.go

@@ -67,6 +67,9 @@ type store struct {
 	root               string
 	ls                 LabelStore
 	integritySupported bool
+
+	locksMu sync.Mutex
+	locks   map[string]*lock
 }
 
 // NewStore returns a local content store
@@ -90,6 +93,7 @@ func NewLabeledStore(root string, ls LabelStore) (content.Store, error) {
 		root:               root,
 		ls:                 ls,
 		integritySupported: supported,
+		locks:              map[string]*lock{},
 	}, nil
 }
 
@@ -464,13 +468,13 @@ func (s *store) Writer(ctx context.Context, opts ...content.WriterOpt) (content.
 		return nil, fmt.Errorf("ref must not be empty: %w", errdefs.ErrInvalidArgument)
 	}
 
-	if err := tryLock(wOpts.Ref); err != nil {
+	if err := s.tryLock(wOpts.Ref); err != nil {
 		return nil, err
 	}
 
 	w, err := s.writer(ctx, wOpts.Ref, wOpts.Desc.Size, wOpts.Desc.Digest)
 	if err != nil {
-		unlock(wOpts.Ref)
+		s.unlock(wOpts.Ref)
 		return nil, err
 	}
 

plugins/content/local/writer.go

@@ -78,7 +78,7 @@ func (w *writer) Write(p []byte) (n int, err error) {
 
 func (w *writer) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
 	// Ensure even on error the writer is fully closed
-	defer unlock(w.ref)
+	defer w.s.unlock(w.ref)
 
 	var base content.Info
 	for _, opt := range opts {
@@ -198,7 +198,7 @@ func (w *writer) Close() (err error) {
 		err = w.fp.Close()
 		writeTimestampFile(filepath.Join(w.path, "updatedat"), w.updatedAt)
 		w.fp = nil
-		unlock(w.ref)
+		w.s.unlock(w.ref)
 		return
 	}