Fix a race condition in pull through cache population by removing the functionality

of readers joining current downloads.  Concurrent requests for the same blob
will not block, but only the first instance will be comitted locally.

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>

docs/proxy/proxyblobstore.go

@@ -22,15 +22,10 @@ type proxyBlobStore struct {
 	scheduler   *scheduler.TTLExpirationScheduler
 }
 
-var _ distribution.BlobStore = proxyBlobStore{}
+var _ distribution.BlobStore = &proxyBlobStore{}
-
-type inflightBlob struct {
-	refCount int
-	bw       distribution.BlobWriter
-}
 
 // inflight tracks currently downloading blobs
-var inflight = make(map[digest.Digest]*inflightBlob)
+var inflight = make(map[digest.Digest]struct{})
 
 // mu protects inflight
 var mu sync.Mutex
@@ -42,140 +37,113 @@ func setResponseHeaders(w http.ResponseWriter, length int64, mediaType string, d
 	w.Header().Set("Etag", digest.String())
 }
 
-func (pbs proxyBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
+func (pbs *proxyBlobStore) copyContent(ctx context.Context, dgst digest.Digest, writer io.Writer) (distribution.Descriptor, error) {
-	desc, err := pbs.localStore.Stat(ctx, dgst)
+	desc, err := pbs.remoteStore.Stat(ctx, dgst)
-	if err != nil && err != distribution.ErrBlobUnknown {
-		return err
-	}
-
-	if err == nil {
-		proxyMetrics.BlobPush(uint64(desc.Size))
-		return pbs.localStore.ServeBlob(ctx, w, r, dgst)
-	}
-
-	desc, err = pbs.remoteStore.Stat(ctx, dgst)
 	if err != nil {
-		return err
+		return distribution.Descriptor{}, err
+	}
+
+	if w, ok := writer.(http.ResponseWriter); ok {
+		setResponseHeaders(w, desc.Size, desc.MediaType, dgst)
 	}
 
 	remoteReader, err := pbs.remoteStore.Open(ctx, dgst)
 	if err != nil {
-		return err
+		return distribution.Descriptor{}, err
 	}
 
-	bw, isNew, cleanup, err := getOrCreateBlobWriter(ctx, pbs.localStore, desc)
+	_, err = io.CopyN(writer, remoteReader, desc.Size)
 	if err != nil {
-		return err
+		return distribution.Descriptor{}, err
 	}
-	defer cleanup()
 
-	if isNew {
+	proxyMetrics.BlobPush(uint64(desc.Size))
-		go func() {
+
-			err := streamToStorage(ctx, remoteReader, desc, bw)
+	return desc, nil
+}
+
+func (pbs *proxyBlobStore) serveLocal(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) (bool, error) {
+	localDesc, err := pbs.localStore.Stat(ctx, dgst)
 	if err != nil {
-				context.GetLogger(ctx).Error(err)
+		// Stat can report a zero sized file here if it's checked between creation
+		// and population.  Return nil error, and continue
+		return false, nil
 	}
 
-			proxyMetrics.BlobPull(uint64(desc.Size))
+	if err == nil {
+		proxyMetrics.BlobPush(uint64(localDesc.Size))
+		return true, pbs.localStore.ServeBlob(ctx, w, r, dgst)
+	}
+
+	return false, nil
+
+}
+
+func (pbs *proxyBlobStore) storeLocal(ctx context.Context, dgst digest.Digest) error {
+	defer func() {
+		mu.Lock()
+		delete(inflight, dgst)
+		mu.Unlock()
 	}()
-		err := streamToClient(ctx, w, desc, bw)
-		if err != nil {
-			return err
-		}
-
-		proxyMetrics.BlobPush(uint64(desc.Size))
-		pbs.scheduler.AddBlob(dgst.String(), blobTTL)
-		return nil
-	}
-
-	err = streamToClient(ctx, w, desc, bw)
-	if err != nil {
-		return err
-	}
-	proxyMetrics.BlobPush(uint64(desc.Size))
-	return nil
-}
-
-type cleanupFunc func()
-
-// getOrCreateBlobWriter will track which blobs are currently being downloaded and enable client requesting
-// the same blob concurrently to read from the existing stream.
-func getOrCreateBlobWriter(ctx context.Context, blobs distribution.BlobService, desc distribution.Descriptor) (distribution.BlobWriter, bool, cleanupFunc, error) {
-	mu.Lock()
-	defer mu.Unlock()
-	dgst := desc.Digest
-
-	cleanup := func() {
-		mu.Lock()
-		defer mu.Unlock()
-		inflight[dgst].refCount--
-
-		if inflight[dgst].refCount == 0 {
-			defer delete(inflight, dgst)
-			_, err := inflight[dgst].bw.Commit(ctx, desc)
-			if err != nil {
-				// There is a narrow race here where Commit can be called while this blob's TTL is expiring
-				// and its being removed from storage.  In that case, the client stream will continue
-				// uninterruped and the blob will be pulled through on the next request, so just log it
-				context.GetLogger(ctx).Errorf("Error committing blob: %q", err)
-			}
-
-		}
-	}
 
+	var desc distribution.Descriptor
+	var err error
 	var bw distribution.BlobWriter
+
+	bw, err = pbs.localStore.Create(ctx)
+	if err != nil {
+		return err
+	}
+
+	desc, err = pbs.copyContent(ctx, dgst, bw)
+	if err != nil {
+		return err
+	}
+
+	_, err = bw.Commit(ctx, desc)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (pbs *proxyBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
+	served, err := pbs.serveLocal(ctx, w, r, dgst)
+	if err != nil {
+		context.GetLogger(ctx).Errorf("Error serving blob from local storage: %s", err.Error())
+		return err
+	}
+
+	if served {
+		return nil
+	}
+
+	mu.Lock()
 	_, ok := inflight[dgst]
 	if ok {
-		bw = inflight[dgst].bw
+		mu.Unlock()
-		inflight[dgst].refCount++
+		_, err := pbs.copyContent(ctx, dgst, w)
-		return bw, false, cleanup, nil
+		return err
 	}
+	inflight[dgst] = struct{}{}
+	mu.Unlock()
 
-	var err error
+	go func(dgst digest.Digest) {
-	bw, err = blobs.Create(ctx)
+		if err := pbs.storeLocal(ctx, dgst); err != nil {
-	if err != nil {
+			context.GetLogger(ctx).Errorf("Error committing to storage: %s", err.Error())
-		return nil, false, nil, err
 		}
+		pbs.scheduler.AddBlob(dgst.String(), repositoryTTL)
+	}(dgst)
 
-	inflight[dgst] = &inflightBlob{refCount: 1, bw: bw}
+	_, err = pbs.copyContent(ctx, dgst, w)
-	return bw, true, cleanup, nil
-}
-
-func streamToStorage(ctx context.Context, remoteReader distribution.ReadSeekCloser, desc distribution.Descriptor, bw distribution.BlobWriter) error {
-	_, err := io.CopyN(bw, remoteReader, desc.Size)
 	if err != nil {
 		return err
 	}
-
 	return nil
 }
 
-func streamToClient(ctx context.Context, w http.ResponseWriter, desc distribution.Descriptor, bw distribution.BlobWriter) error {
+func (pbs *proxyBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
-	setResponseHeaders(w, desc.Size, desc.MediaType, desc.Digest)
-
-	reader, err := bw.Reader()
-	if err != nil {
-		return err
-	}
-	defer reader.Close()
-	teeReader := io.TeeReader(reader, w)
-	buf := make([]byte, 32768, 32786)
-	var soFar int64
-	for {
-		rd, err := teeReader.Read(buf)
-		if err == nil || err == io.EOF {
-			soFar += int64(rd)
-			if soFar < desc.Size {
-				// buffer underflow, keep trying
-				continue
-			}
-			return nil
-		}
-		return err
-	}
-}
-
-func (pbs proxyBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
 	desc, err := pbs.localStore.Stat(ctx, dgst)
 	if err == nil {
 		return desc, err
@@ -189,26 +157,26 @@ func (pbs proxyBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distrib
 }
 
 // Unsupported functions
-func (pbs proxyBlobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
+func (pbs *proxyBlobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
 	return distribution.Descriptor{}, distribution.ErrUnsupported
 }
 
-func (pbs proxyBlobStore) Create(ctx context.Context) (distribution.BlobWriter, error) {
+func (pbs *proxyBlobStore) Create(ctx context.Context) (distribution.BlobWriter, error) {
 	return nil, distribution.ErrUnsupported
 }
 
-func (pbs proxyBlobStore) Resume(ctx context.Context, id string) (distribution.BlobWriter, error) {
+func (pbs *proxyBlobStore) Resume(ctx context.Context, id string) (distribution.BlobWriter, error) {
 	return nil, distribution.ErrUnsupported
 }
 
-func (pbs proxyBlobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {
+func (pbs *proxyBlobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {
 	return nil, distribution.ErrUnsupported
 }
 
-func (pbs proxyBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
+func (pbs *proxyBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
 	return nil, distribution.ErrUnsupported
 }
 
-func (pbs proxyBlobStore) Delete(ctx context.Context, dgst digest.Digest) error {
+func (pbs *proxyBlobStore) Delete(ctx context.Context, dgst digest.Digest) error {
 	return distribution.ErrUnsupported
 }

docs/proxy/proxyblobstore_test.go

@@ -1,10 +1,13 @@
 package proxy
 
 import (
-	"fmt"
+	"io/ioutil"
+	"math/rand"
 	"net/http"
 	"net/http/httptest"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/docker/distribution"
 	"github.com/docker/distribution/context"
@@ -12,75 +15,119 @@ import (
 	"github.com/docker/distribution/registry/proxy/scheduler"
 	"github.com/docker/distribution/registry/storage"
 	"github.com/docker/distribution/registry/storage/cache/memory"
+	"github.com/docker/distribution/registry/storage/driver/filesystem"
 	"github.com/docker/distribution/registry/storage/driver/inmemory"
 )
 
+var sbsMu sync.Mutex
+
 type statsBlobStore struct {
 	stats map[string]int
 	blobs distribution.BlobStore
 }
 
 func (sbs statsBlobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
+	sbsMu.Lock()
 	sbs.stats["put"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Put(ctx, mediaType, p)
 }
 
 func (sbs statsBlobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
+	sbsMu.Lock()
 	sbs.stats["get"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Get(ctx, dgst)
 }
 
 func (sbs statsBlobStore) Create(ctx context.Context) (distribution.BlobWriter, error) {
+	sbsMu.Lock()
 	sbs.stats["create"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Create(ctx)
 }
 
 func (sbs statsBlobStore) Resume(ctx context.Context, id string) (distribution.BlobWriter, error) {
+	sbsMu.Lock()
 	sbs.stats["resume"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Resume(ctx, id)
 }
 
 func (sbs statsBlobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {
+	sbsMu.Lock()
 	sbs.stats["open"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Open(ctx, dgst)
 }
 
 func (sbs statsBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
+	sbsMu.Lock()
 	sbs.stats["serveblob"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.ServeBlob(ctx, w, r, dgst)
 }
 
 func (sbs statsBlobStore) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
+
+	sbsMu.Lock()
 	sbs.stats["stat"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Stat(ctx, dgst)
 }
 
 func (sbs statsBlobStore) Delete(ctx context.Context, dgst digest.Digest) error {
+	sbsMu.Lock()
 	sbs.stats["delete"]++
+	sbsMu.Unlock()
+
 	return sbs.blobs.Delete(ctx, dgst)
 }
 
 type testEnv struct {
+	numUnique int
 	inRemote  []distribution.Descriptor
 	store     proxyBlobStore
 	ctx       context.Context
 }
 
-func (te testEnv) LocalStats() *map[string]int {
+func (te *testEnv) LocalStats() *map[string]int {
+	sbsMu.Lock()
 	ls := te.store.localStore.(statsBlobStore).stats
+	sbsMu.Unlock()
 	return &ls
 }
 
-func (te testEnv) RemoteStats() *map[string]int {
+func (te *testEnv) RemoteStats() *map[string]int {
+	sbsMu.Lock()
 	rs := te.store.remoteStore.(statsBlobStore).stats
+	sbsMu.Unlock()
 	return &rs
 }
 
 // Populate remote store and record the digests
-func makeTestEnv(t *testing.T, name string) testEnv {
+func makeTestEnv(t *testing.T, name string) *testEnv {
 	ctx := context.Background()
 
-	localRegistry, err := storage.NewRegistry(ctx, inmemory.New(), storage.BlobDescriptorCacheProvider(memory.NewInMemoryBlobDescriptorCacheProvider()), storage.EnableRedirect, storage.DisableDigestResumption)
+	truthDir, err := ioutil.TempDir("", "truth")
+	if err != nil {
+		t.Fatalf("unable to create tempdir: %s", err)
+	}
+
+	cacheDir, err := ioutil.TempDir("", "cache")
+	if err != nil {
+		t.Fatalf("unable to create tempdir: %s", err)
+	}
+
+	// todo: create a tempfile area here
+	localRegistry, err := storage.NewRegistry(ctx, filesystem.New(truthDir), storage.BlobDescriptorCacheProvider(memory.NewInMemoryBlobDescriptorCacheProvider()), storage.EnableRedirect, storage.DisableDigestResumption)
 	if err != nil {
 		t.Fatalf("error creating registry: %v", err)
 	}
@@ -89,7 +136,7 @@ func makeTestEnv(t *testing.T, name string) testEnv {
 		t.Fatalf("unexpected error getting repo: %v", err)
 	}
 
-	truthRegistry, err := storage.NewRegistry(ctx, inmemory.New(), storage.BlobDescriptorCacheProvider(memory.NewInMemoryBlobDescriptorCacheProvider()))
+	truthRegistry, err := storage.NewRegistry(ctx, filesystem.New(cacheDir), storage.BlobDescriptorCacheProvider(memory.NewInMemoryBlobDescriptorCacheProvider()))
 	if err != nil {
 		t.Fatalf("error creating registry: %v", err)
 	}
@@ -116,33 +163,59 @@ func makeTestEnv(t *testing.T, name string) testEnv {
 		scheduler:   s,
 	}
 
-	te := testEnv{
+	te := &testEnv{
 		store: proxyBlobStore,
 		ctx:   ctx,
 	}
 	return te
 }
 
-func populate(t *testing.T, te *testEnv, blobCount int) {
+func makeBlob(size int) []byte {
-	var inRemote []distribution.Descriptor
+	blob := make([]byte, size, size)
-	for i := 0; i < blobCount; i++ {
+	for i := 0; i < size; i++ {
-		bytes := []byte(fmt.Sprintf("blob%d", i))
+		blob[i] = byte('A' + rand.Int()%48)
+	}
+	return blob
+}
 
+func init() {
+	rand.Seed(42)
+}
+
+func perm(m []distribution.Descriptor) []distribution.Descriptor {
+	for i := 0; i < len(m); i++ {
+		j := rand.Intn(i + 1)
+		tmp := m[i]
+		m[i] = m[j]
+		m[j] = tmp
+	}
+	return m
+}
+
+func populate(t *testing.T, te *testEnv, blobCount, size, numUnique int) {
+	var inRemote []distribution.Descriptor
+
+	for i := 0; i < numUnique; i++ {
+		bytes := makeBlob(size)
+		for j := 0; j < blobCount/numUnique; j++ {
 			desc, err := te.store.remoteStore.Put(te.ctx, "", bytes)
 			if err != nil {
-			t.Errorf("Put in store")
+				t.Fatalf("Put in store")
 			}
+
 			inRemote = append(inRemote, desc)
 		}
+	}
 
 	te.inRemote = inRemote
-
+	te.numUnique = numUnique
 }
 
 func TestProxyStoreStat(t *testing.T) {
 	te := makeTestEnv(t, "foo/bar")
+
 	remoteBlobCount := 1
-	populate(t, &te, remoteBlobCount)
+	populate(t, te, remoteBlobCount, 10, 1)
 
 	localStats := te.LocalStats()
 	remoteStats := te.RemoteStats()
@@ -164,43 +237,91 @@ func TestProxyStoreStat(t *testing.T) {
 	}
 }
 
-func TestProxyStoreServe(t *testing.T) {
+func TestProxyStoreServeHighConcurrency(t *testing.T) {
 	te := makeTestEnv(t, "foo/bar")
-	remoteBlobCount := 1
+	blobSize := 200
-	populate(t, &te, remoteBlobCount)
+	blobCount := 10
+	numUnique := 1
+	populate(t, te, blobCount, blobSize, numUnique)
 
+	numClients := 16
+	testProxyStoreServe(t, te, numClients)
+}
+
+func TestProxyStoreServeMany(t *testing.T) {
+	te := makeTestEnv(t, "foo/bar")
+	blobSize := 200
+	blobCount := 10
+	numUnique := 4
+	populate(t, te, blobCount, blobSize, numUnique)
+
+	numClients := 4
+	testProxyStoreServe(t, te, numClients)
+}
+
+// todo(richardscothern): blobCount must be smaller than num clients
+func TestProxyStoreServeBig(t *testing.T) {
+	te := makeTestEnv(t, "foo/bar")
+
+	blobSize := 2 << 20
+	blobCount := 4
+	numUnique := 2
+	populate(t, te, blobCount, blobSize, numUnique)
+
+	numClients := 4
+	testProxyStoreServe(t, te, numClients)
+}
+
+// testProxyStoreServe will create clients to consume all blobs
+// populated in the truth store
+func testProxyStoreServe(t *testing.T, te *testEnv, numClients int) {
 	localStats := te.LocalStats()
 	remoteStats := te.RemoteStats()
 
+	var wg sync.WaitGroup
+
+	for i := 0; i < numClients; i++ {
 		// Serveblob - pulls through blobs
-	for _, dr := range te.inRemote {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for _, remoteBlob := range te.inRemote {
 				w := httptest.NewRecorder()
 				r, err := http.NewRequest("GET", "", nil)
 				if err != nil {
 					t.Fatal(err)
 				}
 
-		err = te.store.ServeBlob(te.ctx, w, r, dr.Digest)
+				err = te.store.ServeBlob(te.ctx, w, r, remoteBlob.Digest)
 				if err != nil {
 					t.Fatalf(err.Error())
 				}
 
-		dl, err := digest.FromBytes(w.Body.Bytes())
+				bodyBytes := w.Body.Bytes()
+				localDigest, err := digest.FromBytes(bodyBytes)
 				if err != nil {
 					t.Fatalf("Error making digest from blob")
 				}
-		if dl != dr.Digest {
+				if localDigest != remoteBlob.Digest {
-			t.Errorf("Mismatching blob fetch from proxy")
+					t.Fatalf("Mismatching blob fetch from proxy")
 				}
 			}
+		}()
+	}
 
-	if (*localStats)["stat"] != remoteBlobCount && (*localStats)["create"] != remoteBlobCount {
+	wg.Wait()
-		t.Fatalf("unexpected local stats")
+
-	}
+	remoteBlobCount := len(te.inRemote)
-	if (*remoteStats)["stat"] != remoteBlobCount && (*remoteStats)["open"] != remoteBlobCount {
+	if (*localStats)["stat"] != remoteBlobCount*numClients && (*localStats)["create"] != te.numUnique {
-		t.Fatalf("unexpected local stats")
+		t.Fatal("Expected: stat:", remoteBlobCount*numClients, "create:", remoteBlobCount)
 	}
 
+	// Wait for any async storage goroutines to finish
+	time.Sleep(3 * time.Second)
+
+	remoteStatCount := (*remoteStats)["stat"]
+	remoteOpenCount := (*remoteStats)["open"]
+
 	// Serveblob - blobs come from local
 	for _, dr := range te.inRemote {
 		w := httptest.NewRecorder()
@@ -223,15 +344,11 @@ func TestProxyStoreServe(t *testing.T) {
 		}
 	}
 
-	// Stat to find local, but no new blobs were created
+	localStats = te.LocalStats()
-	if (*localStats)["stat"] != remoteBlobCount*2 && (*localStats)["create"] != remoteBlobCount*2 {
+	remoteStats = te.RemoteStats()
-		t.Fatalf("unexpected local stats")
-	}
 
-	// Remote unchanged
+	// Ensure remote unchanged
-	if (*remoteStats)["stat"] != remoteBlobCount && (*remoteStats)["open"] != remoteBlobCount {
+	if (*remoteStats)["stat"] != remoteStatCount && (*remoteStats)["open"] != remoteOpenCount {
-		fmt.Printf("\tlocal=%#v, \n\tremote=%#v\n", localStats, remoteStats)
+		t.Fatalf("unexpected remote stats: %#v", remoteStats)
-		t.Fatalf("unexpected local stats")
 	}
-
 }

docs/proxy/proxyregistry.go

@@ -94,7 +94,7 @@ func (pr *proxyingRegistry) Repository(ctx context.Context, name string) (distri
 	}
 
 	return &proxiedRepository{
-		blobStore: proxyBlobStore{
+		blobStore: &proxyBlobStore{
 			localStore:  localRepo.Blobs(ctx),
 			remoteStore: remoteRepo.Blobs(ctx),
 			scheduler:   pr.scheduler,