Open cache interface

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

docs/storage/blobcachemetrics.go

@@ -0,0 +1,60 @@
+package storage
+
+import (
+	"expvar"
+	"sync/atomic"
+
+	"github.com/docker/distribution/registry/storage/cache"
+)
+
+type blobStatCollector struct {
+	metrics cache.Metrics
+}
+
+func (bsc *blobStatCollector) Hit() {
+	atomic.AddUint64(&bsc.metrics.Requests, 1)
+	atomic.AddUint64(&bsc.metrics.Hits, 1)
+}
+
+func (bsc *blobStatCollector) Miss() {
+	atomic.AddUint64(&bsc.metrics.Requests, 1)
+	atomic.AddUint64(&bsc.metrics.Misses, 1)
+}
+
+func (bsc *blobStatCollector) Metrics() cache.Metrics {
+	return bsc.metrics
+}
+
+// blobStatterCacheMetrics keeps track of cache metrics for blob descriptor
+// cache requests. Note this is kept globally and made available via expvar.
+// For more detailed metrics, its recommend to instrument a particular cache
+// implementation.
+var blobStatterCacheMetrics cache.MetricsTracker = &blobStatCollector{}
+
+func init() {
+	registry := expvar.Get("registry")
+	if registry == nil {
+		registry = expvar.NewMap("registry")
+	}
+
+	cache := registry.(*expvar.Map).Get("cache")
+	if cache == nil {
+		cache = &expvar.Map{}
+		cache.(*expvar.Map).Init()
+		registry.(*expvar.Map).Set("cache", cache)
+	}
+
+	storage := cache.(*expvar.Map).Get("storage")
+	if storage == nil {
+		storage = &expvar.Map{}
+		storage.(*expvar.Map).Init()
+		cache.(*expvar.Map).Set("storage", storage)
+	}
+
+	storage.(*expvar.Map).Set("blobdescriptor", expvar.Func(func() interface{} {
+		// no need for synchronous access: the increments are atomic and
+		// during reading, we don't care if the data is up to date. The
+		// numbers will always *eventually* be reported correctly.
+		return blobStatterCacheMetrics
+	}))
+}

docs/storage/cache/cachedblobdescriptorstore.go

@@ -0,0 +1,80 @@
+package cache
+
+import (
+	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/digest"
+
+	"github.com/docker/distribution"
+)
+
+// Metrics is used to hold metric counters
+// related to the number of times a cache was
+// hit or missed.
+type Metrics struct {
+	Requests uint64
+	Hits     uint64
+	Misses   uint64
+}
+
+// MetricsTracker represents a metric tracker
+// which simply counts the number of hits and misses.
+type MetricsTracker interface {
+	Hit()
+	Miss()
+	Metrics() Metrics
+}
+
+type cachedBlobStatter struct {
+	cache   distribution.BlobDescriptorService
+	backend distribution.BlobStatter
+	tracker MetricsTracker
+}
+
+// NewCachedBlobStatter creates a new statter which prefers a cache and
+// falls back to a backend.
+func NewCachedBlobStatter(cache distribution.BlobDescriptorService, backend distribution.BlobStatter) distribution.BlobStatter {
+	return &cachedBlobStatter{
+		cache:   cache,
+		backend: backend,
+	}
+}
+
+// NewCachedBlobStatterWithMetrics creates a new statter which prefers a cache and
+// falls back to a backend. Hits and misses will send to the tracker.
+func NewCachedBlobStatterWithMetrics(cache distribution.BlobDescriptorService, backend distribution.BlobStatter, tracker MetricsTracker) distribution.BlobStatter {
+	return &cachedBlobStatter{
+		cache:   cache,
+		backend: backend,
+		tracker: tracker,
+	}
+}
+
+func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
+	desc, err := cbds.cache.Stat(ctx, dgst)
+	if err != nil {
+		if err != distribution.ErrBlobUnknown {
+			context.GetLogger(ctx).Errorf("error retrieving descriptor from cache: %v", err)
+		}
+
+		goto fallback
+	}
+
+	if cbds.tracker != nil {
+		cbds.tracker.Hit()
+	}
+	return desc, nil
+fallback:
+	if cbds.tracker != nil {
+		cbds.tracker.Miss()
+	}
+	desc, err = cbds.backend.Stat(ctx, dgst)
+	if err != nil {
+		return desc, err
+	}
+
+	if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
+		context.GetLogger(ctx).Errorf("error adding descriptor %v to cache: %v", desc.Digest, err)
+	}
+
+	return desc, err
+}

docs/storage/cachedblobdescriptorstore.go

@@ -1,84 +0,0 @@
-package storage
-
-import (
-	"expvar"
-	"sync/atomic"
-
-	"github.com/docker/distribution/context"
-	"github.com/docker/distribution/digest"
-
-	"github.com/docker/distribution"
-)
-
-type cachedBlobStatter struct {
-	cache   distribution.BlobDescriptorService
-	backend distribution.BlobStatter
-}
-
-func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
-	atomic.AddUint64(&blobStatterCacheMetrics.Stat.Requests, 1)
-	desc, err := cbds.cache.Stat(ctx, dgst)
-	if err != nil {
-		if err != distribution.ErrBlobUnknown {
-			context.GetLogger(ctx).Errorf("error retrieving descriptor from cache: %v", err)
-		}
-
-		goto fallback
-	}
-
-	atomic.AddUint64(&blobStatterCacheMetrics.Stat.Hits, 1)
-	return desc, nil
-fallback:
-	atomic.AddUint64(&blobStatterCacheMetrics.Stat.Misses, 1)
-	desc, err = cbds.backend.Stat(ctx, dgst)
-	if err != nil {
-		return desc, err
-	}
-
-	if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
-		context.GetLogger(ctx).Errorf("error adding descriptor %v to cache: %v", desc.Digest, err)
-	}
-
-	return desc, err
-}
-
-// blobStatterCacheMetrics keeps track of cache metrics for blob descriptor
-// cache requests. Note this is kept globally and made available via expvar.
-// For more detailed metrics, its recommend to instrument a particular cache
-// implementation.
-var blobStatterCacheMetrics struct {
-	// Stat tracks calls to the caches.
-	Stat struct {
-		Requests uint64
-		Hits     uint64
-		Misses   uint64
-	}
-}
-
-func init() {
-	registry := expvar.Get("registry")
-	if registry == nil {
-		registry = expvar.NewMap("registry")
-	}
-
-	cache := registry.(*expvar.Map).Get("cache")
-	if cache == nil {
-		cache = &expvar.Map{}
-		cache.(*expvar.Map).Init()
-		registry.(*expvar.Map).Set("cache", cache)
-	}
-
-	storage := cache.(*expvar.Map).Get("storage")
-	if storage == nil {
-		storage = &expvar.Map{}
-		storage.(*expvar.Map).Init()
-		cache.(*expvar.Map).Set("storage", storage)
-	}
-
-	storage.(*expvar.Map).Set("blobdescriptor", expvar.Func(func() interface{} {
-		// no need for synchronous access: the increments are atomic and
-		// during reading, we don't care if the data is up to date. The
-		// numbers will always *eventually* be reported correctly.
-		return blobStatterCacheMetrics
-	}))
-}

docs/storage/registry.go

@@ -29,10 +29,7 @@ func NewRegistryWithDriver(ctx context.Context, driver storagedriver.StorageDriv
 	}
 
 	if blobDescriptorCacheProvider != nil {
-		statter = &cachedBlobStatter{
+		statter = cache.NewCachedBlobStatter(blobDescriptorCacheProvider, statter)
-			cache:   blobDescriptorCacheProvider,
-			backend: statter,
-		}
 	}
 
 	bs := &blobStore{
@@ -143,10 +140,7 @@ func (repo *repository) Blobs(ctx context.Context) distribution.BlobStore {
 	}
 
 	if repo.descriptorCache != nil {
-		statter = &cachedBlobStatter{
+		statter = cache.NewCachedBlobStatter(repo.descriptorCache, statter)
-			cache:   repo.descriptorCache,
-			backend: statter,
-		}
 	}
 
 	return &linkedBlobStore{