[GitHub] [arrow] lidavidm commented on a diff in pull request #36205: GH-16604: [C++][FlightRPC] Add async Flight client

["lidavidm (via GitHub)" <gi...@apache.org>]

lidavidm commented on code in PR #36205:
URL: https://github.com/apache/arrow/pull/36205#discussion_r1238773601


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cpp/src/arrow/flight/types_async.h:
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@@ -0,0 +1,116 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#pragma once
+
+#include <memory>
+
+#include "arrow/flight/type_fwd.h"
+#include "arrow/flight/types.h"
+#include "arrow/ipc/options.h"
+#include "arrow/type_fwd.h"
+
+namespace arrow::flight {
+
+class IpcPutter;
+
+/// \defgroup flight-async Async Flight Types
+/// Common types used for asynchronous Flight APIs.
+/// @{
+
+/// \brief Non-templated state for an async RPC.
+class AsyncListenerBase {
+ public:
+  AsyncListenerBase();
+  virtual ~AsyncListenerBase();
+
+  /// \brief Request cancellation of the RPC.
+  ///
+  /// The RPC is not cancelled until AsyncListener::OnFinish is called.
+  void TryCancel();
+
+ private:
+  friend class arrow::flight::internal::ClientTransport;
+  friend class arrow::flight::IpcPutter;
+
+  /// Transport-specific state for this RPC.  Transport
+  /// implementations may store and retrieve state here via
+  /// ClientTransport::SetAsyncRpc and ClientTransport::GetAsyncRpc.
+  std::unique_ptr<internal::AsyncRpc> rpc_state_;
+};
+
+/// \brief Callbacks for results from async RPCs.
+///
+/// A single listener may not be used for multiple concurrent RPC
+/// calls.  The application MUST hold the listener alive until
+/// OnFinish() is called and has finished.
+template <typename T>
+class ARROW_FLIGHT_EXPORT AsyncListener : public AsyncListenerBase {
+ public:
+  /// \brief Get the next server result.
+  /// This will never be called concurrently with itself or OnFinish.
+  virtual void OnNext(T message) = 0;

Review Comment:
   I think it's best to not have multiple error paths. If we return a Status here, what is the implementation supposed to do with it? It can at best just give it straight back to OnFinish.



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