@@ -1,16 +1,18 @@

 package memory

 import (

+	"sync"

 	"time"

 	"github.com/docker/docker/pkg/discovery"

 )

-// Discovery implements a descovery backend that keeps

+// Discovery implements a discovery backend that keeps

 // data in memory.

 type Discovery struct {

 	heartbeat time.Duration

 	values    []string

+	mu        sync.Mutex

 }

 func init() {

@@ -41,21 +43,27 @@ func (s *Discovery) Watch(stopCh <-chan struct{}) (<-chan discovery.Entries, <-c

 		// Send the initial entries if available.

 		var currentEntries discovery.Entries

+		var err error

+

+		s.mu.Lock()

 		if len(s.values) > 0 {

-			var err error

 			currentEntries, err = discovery.CreateEntries(s.values)

-			if err != nil {

-				errCh <- err

-			} else {

-				ch <- currentEntries

-			}

+		}

+		s.mu.Unlock()

+

+		if err != nil {

+			errCh <- err

+		} else if currentEntries != nil {

+			ch <- currentEntries

 		}

 		// Periodically send updates.

 		for {

 			select {

 			case <-ticker.C:

+				s.mu.Lock()

 				newEntries, err := discovery.CreateEntries(s.values)

+				s.mu.Unlock()

 				if err != nil {

 					errCh <- err

 					continue

@@ -78,6 +86,8 @@ func (s *Discovery) Watch(stopCh <-chan struct{}) (<-chan discovery.Entries, <-c

 // Register adds a new address to the discovery.

 func (s *Discovery) Register(addr string) error {

+	s.mu.Lock()

 	s.values = append(s.values, addr)

+	s.mu.Unlock()

 	return nil

 }