Define a DLocker interface for distributed locker

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

contrib/lock/client/client.go

@@ -121,11 +121,12 @@ func main() {
 	locker := concurrency.NewLocker(session, "/lock")
 	locker.Lock()
 	defer locker.Unlock()
-	version := session.Lease()
+	leaseID := session.Lease()
+	version := locker.Rev()
 	log.Printf("acquired lock, version: %x", version)
 
 	if mode == 1 {
-		log.Printf("please manually revoke the lease using 'etcdctl lease revoke %x' or wait for it to expire, then start executing client 2 and hit any key...", version)
+		log.Printf("please manually revoke the lease using 'etcdctl lease revoke %x' or wait for it to expire, then start executing client 2 and hit any key...", leaseID)
 		reader := bufio.NewReader(os.Stdin)
 		_, _ = reader.ReadByte()
 		log.Print("resuming client 1")