fix prefetch bugs, optimize code

paddle/fluid/framework/selected_rows.cc

@@ -121,24 +121,29 @@ bool SelectedRows::HasKey(int64_t key) const {
 }
 
 std::vector<std::pair<int64_t, int64_t>> SelectedRows::Get(
-    std::vector<int64_t> keys, framework::Tensor* value) const {
+    const std::vector<int64_t>& keys, framework::Tensor* value) const {
   PADDLE_ENFORCE(value->IsInitialized(),
                  "The value tensor should be initialized.");
   std::vector<std::pair<int64_t, int64_t>> non_keys_pair;
-  int64_t value_width = value_->numel() / value_->dims()[0];
-  PADDLE_ENFORCE_EQ(value_width, value->numel() / value->dims()[0],
-                    "output tensor should have the same shape with table "
-                    "execpt the dims[0].");
-
-  for (size_t i = 0; i < keys.size(); ++i) {
-    int64_t index = Index(keys[i]);
-    if (index == -1) {
-      non_keys_pair.push_back(std::make_pair(keys[i], static_cast<int64_t>(i)));
-    } else {
-      framework::VisitDataType(
-          framework::ToDataType(value_->type()),
-          TensorCopyVisitor(value, i * value_width, *value_.get(),
-                            index * value_width, value_width));
+  if (keys.empty()) {
+    VLOG(3) << "keys is empty, please check data!";
+  } else {
+    int64_t value_width = value_->numel() / value_->dims()[0];
+    PADDLE_ENFORCE_EQ(value_width, value->numel() / value->dims()[0],
+                      "output tensor should have the same shape with table "
+                      "except the dims[0].");
+
+    for (size_t i = 0; i < keys.size(); ++i) {
+      int64_t index = Index(keys[i]);
+      if (index == -1) {
+        non_keys_pair.push_back(
+            std::make_pair(keys[i], static_cast<int64_t>(i)));
+      } else {
+        framework::VisitDataType(
+            framework::ToDataType(value_->type()),
+            TensorCopyVisitor(value, i * value_width, *value_.get(),
+                              index * value_width, value_width));
+      }
     }
   }
   return non_keys_pair;

paddle/fluid/framework/selected_rows.h

@@ -82,7 +82,7 @@ class SelectedRows {
    * @return a list of pair which contains the non-exists key and the index in
    * the value
    */
-  std::vector<std::pair<int64_t, int64_t>> Get(std::vector<int64_t> keys,
+  std::vector<std::pair<int64_t, int64_t>> Get(const std::vector<int64_t>& keys,
                                                framework::Tensor* value) const;
 
   /*

paddle/fluid/operators/detail/grpc_server.cc

@@ -177,11 +177,8 @@ class RequestPrefetch final : public RequestBase {
         program_(program),
         prefetch_ctx_(prefetch_ctx),
         req_id_(req_id) {
-    if (sync_mode_) {
-      request_.reset(new VariableResponse(scope, dev_ctx_, false));
-    } else {
-      request_.reset(new VariableResponse(scope, dev_ctx_, true));
-    }
+    // prefetch always create a new sub scope
+    request_.reset(new VariableResponse(scope, dev_ctx_, true));
     int method_id = static_cast<int>(detail::GrpcMethod::kPrefetchVariable);
     service_->RequestAsyncUnary(
         method_id, &ctx_, request_.get(), &responder_, cq_, cq_,
@@ -198,10 +195,10 @@ class RequestPrefetch final : public RequestBase {
     std::string var_name = request_->OutVarname();
     VLOG(3) << "RequestPrefetch " << var_name;
     auto var_desc = program_->Block(0).FindVar(var_name);
-    framework::Scope* local_scope = &scope_->NewScope();
+    framework::Scope* local_scope = request_->GetMutableLocalScope();
     auto* var = local_scope->FindVar(var_name);
     InitializeVariable(var, var_desc->GetType());
-    executor_->RunPreparedContext(prefetch_ctx_, scope_);
+    executor_->RunPreparedContext(prefetch_ctx_, local_scope);
 
     SerializeToByteBuffer(var_name, var, *dev_ctx_, &reply_);