Finish the multiplex implementation

examples/server_calling_server.rs

@@ -10,9 +10,10 @@
 extern crate tarpc;
 extern crate futures;
 
-use futures::{BoxFuture, Future};
 use add::{FutureService as AddFutureService, FutureServiceExt as AddExt};
 use double::{FutureService as DoubleFutureService, FutureServiceExt as DoubleExt};
+use futures::{BoxFuture, Future};
+use std::sync::{Arc, Mutex};
 use tarpc::util::{FirstSocketAddr, Message, Never};
 use tarpc::future::Connect as Fc;
 use tarpc::sync::Connect as Sc;
@@ -46,7 +47,15 @@ impl AddFutureService for AddServer {
 
 #[derive(Clone)]
 struct DoubleServer {
-    client: add::FutureClient,
+    client: Arc<Mutex<add::FutureClient>>,
+}
+
+impl DoubleServer {
+    fn new(client: add::FutureClient) -> Self {
+        DoubleServer {
+            client: Arc::new(Mutex::new(client))
+        }
+    }
 }
 
 impl DoubleFutureService for DoubleServer {
@@ -54,6 +63,8 @@ impl DoubleFutureService for DoubleServer {
 
     fn double(&self, x: i32) -> Self::DoubleFut {
         self.client
+            .lock()
+            .unwrap()
             .add(x, x)
             .map_err(|e| e.to_string().into())
             .boxed()
@@ -63,7 +74,7 @@ impl DoubleFutureService for DoubleServer {
 fn main() {
     let add = AddServer.listen("localhost:0".first_socket_addr()).wait().unwrap();
     let add_client = add::FutureClient::connect(add.local_addr()).wait().unwrap();
-    let double = DoubleServer { client: add_client };
+    let double = DoubleServer::new(add_client);
     let double = double.listen("localhost:0".first_socket_addr()).wait().unwrap();
 
     let double_client = double::SyncClient::connect(double.local_addr()).unwrap();