update by comment

paddle/fluid/operators/send_vars_op.cc

@@ -53,7 +53,7 @@ class SendVarsOp : public framework::OperatorBase {
     auto ins = Inputs("X");
 
     std::vector<std::string> epmap = Attr<std::vector<std::string>>("epmap");
-    int flag_wait = Attr<int>("wait");
+    int sync_send = Attr<int>("sync_sent");
 
     platform::DeviceContextPool& pool = platform::DeviceContextPool::Instance();
     auto& ctx = *pool.Get(place);
@@ -68,12 +68,14 @@ class SendVarsOp : public framework::OperatorBase {
     for (size_t i = 0; i < ins.size(); i++) {
       if (NeedSend(scope, ins[i])) {
         VLOG(3) << "sending " << ins[i] << " to " << epmap[i];
+        // TODO(Yancey1989): we need to use an IO threadpool which has
+        // a larger number of threads than the computing threadpool.
         rpc_client->AsyncSendVariable(epmap[i], ctx, scope, ins[i]);
       } else {
         VLOG(3) << "don't send no-initialied variable: " << ins[i];
       }
     }
-    if (flag_wait) {
+    if (sync_send) {
       rpc_client->Wait();
     }
   }
@@ -86,16 +88,16 @@ class SendVarsOpMaker : public framework::OpProtoAndCheckerMaker {
     AddInput("X", "(Tensor, SelectedRows) Input variables to be sent")
         .AsDuplicable();
     AddOutput("RPCClient",
-              "(RPCClient) The RPC client object which is"
+              "(RPCClient) The RPC client object which will be"
               "initialized at most once.");
     AddComment(R"DOC(
 Send operator
 
 This operator will send variables to listen_and_serve op at the parameter server.
 )DOC");
-    AddAttr<int>("wait",
+    AddAttr<int>("ync_send",
                  "(int, default 0)"
-                 "whether watting for all send request have been sent.")
+                 "sync send or async send.")
         .SetDefault(0);
     AddAttr<std::vector<std::string>>("epmap",
                                       "(string vector, default 127.0.0.1:6164)"