Replace imageMutex with Locker pkg

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

graph/graph.go

@@ -22,6 +22,7 @@ import (
 	"github.com/docker/docker/image"
 	"github.com/docker/docker/pkg/archive"
 	"github.com/docker/docker/pkg/idtools"
+	"github.com/docker/docker/pkg/locker"
 	"github.com/docker/docker/pkg/progressreader"
 	"github.com/docker/docker/pkg/streamformatter"
 	"github.com/docker/docker/pkg/stringid"
@@ -100,7 +101,7 @@ type Graph struct {
 	idIndex          *truncindex.TruncIndex
 	driver           graphdriver.Driver
 	imagesMutex      sync.Mutex
-	imageMutex       imageMutex // protect images in driver.
+	imageMutex       locker.Locker // protect images in driver.
 	retained         *retainedLayers
 	tarSplitDisabled bool
 	uidMaps          []idtools.IDMap

graph/mutex.go

@@ -1,45 +0,0 @@
-package graph
-
-import "sync"
-
-// imageMutex provides a lock per image id to protect shared resources in the
-// graph. This is only used with registration but should be used when
-// manipulating the layer store.
-type imageMutex struct {
-	mus map[string]*sync.Mutex // mutexes by image id.
-	mu  sync.Mutex             // protects lock map
-
-	// NOTE(stevvooe): The map above will grow to the size of all images ever
-	// registered during a daemon run. To free these resources, we must
-	// deallocate after unlock. Doing this safely is non-trivial in the face
-	// of a very minor leak.
-}
-
-// Lock the provided id.
-func (im *imageMutex) Lock(id string) {
-	im.getImageLock(id).Lock()
-}
-
-// Unlock the provided id.
-func (im *imageMutex) Unlock(id string) {
-	im.getImageLock(id).Unlock()
-}
-
-// getImageLock returns the mutex for the given id. This method will never
-// return nil.
-func (im *imageMutex) getImageLock(id string) *sync.Mutex {
-	im.mu.Lock()
-	defer im.mu.Unlock()
-
-	if im.mus == nil { // lazy
-		im.mus = make(map[string]*sync.Mutex)
-	}
-
-	mu, ok := im.mus[id]
-	if !ok {
-		mu = new(sync.Mutex)
-		im.mus[id] = mu
-	}
-
-	return mu
-}