revert RequestGetHandler

Author: jacquesqiao

paddle/fluid/operators/distributed/request_handler_impl.cc

@@ -100,25 +100,21 @@ bool RequestGetHandler::Handle(const std::string& varname,
     }
   } else {
     if (varname != FETCH_BARRIER_MESSAGE && varname != COMPLETE_MESSAGE) {
-      PADDLE_THROW(
-          "async mode should not send FETCH_BARRIER_MESSAGE or "
-          "COMPLETE_MESSAGE");
-    }
-
-    if (enable_dc_asgd_) {
-      // NOTE: the format is determined by distributed_transpiler.py
-      std::string param_bak_name =
-          string::Sprintf("%s.trainer_%d_bak", varname, trainer_id);
-      VLOG(3) << "getting " << param_bak_name << " trainer_id " << trainer_id;
-      auto var = scope_->FindVar(varname);
-      auto t_orig = var->Get<framework::LoDTensor>();
-      auto param_bak = scope_->Var(param_bak_name);
-      auto t = param_bak->GetMutable<framework::LoDTensor>();
-      t->mutable_data(dev_ctx_->GetPlace(), t_orig.type());
-      VLOG(3) << "copying " << varname << " to " << param_bak_name;
-      framework::TensorCopy(t_orig, dev_ctx_->GetPlace(), t);
+      if (enable_dc_asgd_) {
+        // NOTE: the format is determined by distributed_transpiler.py
+        std::string param_bak_name =
+            string::Sprintf("%s.trainer_%d_bak", varname, trainer_id);
+        VLOG(3) << "getting " << param_bak_name << " trainer_id " << trainer_id;
+        auto var = scope_->FindVar(varname);
+        auto t_orig = var->Get<framework::LoDTensor>();
+        auto param_bak = scope_->Var(param_bak_name);
+        auto t = param_bak->GetMutable<framework::LoDTensor>();
+        t->mutable_data(dev_ctx_->GetPlace(), t_orig.type());
+        VLOG(3) << "copying " << varname << " to " << param_bak_name;
+        framework::TensorCopy(t_orig, dev_ctx_->GetPlace(), t);
+      }
+      *outvar = scope_->FindVar(varname);
     }
-    *outvar = scope_->FindVar(varname);
   }
   return true;
 }