fix protobuf memory leak (#11177)

fix protobuf memory leak

paddle/fluid/framework/block_desc.cc

@@ -169,17 +169,13 @@ void BlockDesc::Flush() {
   }
 
   if (need_update_) {
-    auto &op_field = *this->desc_->mutable_ops();
-    this->ClearPBOps();
-    op_field.Reserve(static_cast<int>(ops_.size()));
+    this->desc_->mutable_ops()->Clear();
     for (auto &op_desc : ops_) {
-      op_field.AddAllocated(op_desc->Proto());
+      this->desc_->mutable_ops()->Add()->CopyFrom(*op_desc->Proto());
     }
-    auto &var_field = *this->desc_->mutable_vars();
-    this->ClearPBVars();
-    var_field.Reserve(static_cast<int>(vars_.size()));
+    this->desc_->mutable_vars()->Clear();
     for (auto &var_desc : vars_) {
-      var_field.AddAllocated(var_desc.second->Proto());
+      this->desc_->mutable_vars()->Add()->CopyFrom(*var_desc.second->Proto());
     }
     need_update_ = false;
   }
@@ -217,22 +213,6 @@ BlockDesc::BlockDesc(const BlockDesc &other, proto::BlockDesc *desc,
   }
 }
 
-void BlockDesc::ClearPBOps() {
-  auto ops = this->desc_->mutable_ops();
-  while (!ops->empty()) {
-    // we do not own the OpDesc, so release the ownership.
-    ops->ReleaseLast();
-  }
-}
-
-void BlockDesc::ClearPBVars() {
-  auto vars = this->desc_->mutable_vars();
-  while (!vars->empty()) {
-    // we do not own the VarDesc, so release the ownership.
-    vars->ReleaseLast();
-  }
-}
-
 void BlockDesc::SetForwardBlockID(int32_t forward_block_id) {
   PADDLE_ENFORCE(!desc_->has_forward_block_idx(),
                  "Parent block ID has been set to %d. Cannot set to %d",

paddle/fluid/framework/block_desc.h

@@ -41,11 +41,6 @@ class BlockDesc {
 
   BlockDesc(const BlockDesc &other, proto::BlockDesc *desc, ProgramDesc *prog);
 
-  ~BlockDesc() {
-    this->ClearPBVars();
-    this->ClearPBOps();
-  }
-
   int32_t ID() const { return desc_->idx(); }
 
   int32_t Parent() const { return desc_->parent_idx(); }
@@ -113,10 +108,6 @@ class BlockDesc {
 
   ProgramDesc *Program() const { return this->prog_; }
 
- private:
-  void ClearPBOps();
-  void ClearPBVars();
-
  private:
   ProgramDesc *prog_;       // not_own
   proto::BlockDesc *desc_;  // not_own