feat grpc: update to grpc 1.53.1

update grpc to 1.53.1
update grpcio/py3 to 1.53.1

Added patches:
    22-grpc-code-output.patch - allow translation of grpc code to internal string type.
    23-max-thread-limitation.patch - to provide interface for settings of thread number limit, as
    grpc::DynamicThreadPool doesn't provide interface to limit thread number anymore.
    24-support_for-non-abort-grpc.patch - generate exception instead of application crash
    25-forkable-destruction-order.patch - correct forkable logic for TimerManager
    27-skip-child-post-fork-operations.patch - allow to skip child post fork operations to exclude UB (used for unified agent only)
    pr33495_fox_nested_fork.patch - fix issues with nested forks
    pr33582_fork_handler.patch - disable fork handler support  if it is not requested intentionally

1 files changed, 791 insertions, 18 deletions

diff --git a/contrib/libs/grpc/include/grpcpp/support/server_callback.h b/contrib/libs/grpc/include/grpcpp/support/server_callback.h
index 1ffdce53d9..5cd4df28a3 100644
--- a/contrib/libs/grpc/include/grpcpp/support/server_callback.h
+++ b/contrib/libs/grpc/include/grpcpp/support/server_callback.h
@@ -1,24 +1,797 @@
-/*
- *
- * Copyright 2018 gRPC authors.
- *
- * Licensed 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.
- *
- */
+//
+//
+// Copyright 2018 gRPC authors.
+//
+// Licensed 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.
+//
+//
 
 #ifndef GRPCPP_SUPPORT_SERVER_CALLBACK_H
 #define GRPCPP_SUPPORT_SERVER_CALLBACK_H
 
-#include <grpcpp/impl/codegen/server_callback.h>  // IWYU pragma: export
+#include <atomic>
+#include <functional>
+#include <type_traits>
+
+#include <grpcpp/impl/call.h>
+#include <grpcpp/impl/call_op_set.h>
+#include <grpcpp/impl/sync.h>
+#include <grpcpp/support/callback_common.h>
+#include <grpcpp/support/config.h>
+#include <grpcpp/support/message_allocator.h>
+#include <grpcpp/support/status.h>
+
+namespace grpc {
+
+// Declare base class of all reactors as internal
+namespace internal {
+
+// Forward declarations
+template <class Request, class Response>
+class CallbackUnaryHandler;
+template <class Request, class Response>
+class CallbackClientStreamingHandler;
+template <class Request, class Response>
+class CallbackServerStreamingHandler;
+template <class Request, class Response>
+class CallbackBidiHandler;
+
+class ServerReactor {
+ public:
+  virtual ~ServerReactor() = default;
+  virtual void OnDone() = 0;
+  virtual void OnCancel() = 0;
+
+  // The following is not API. It is for internal use only and specifies whether
+  // all reactions of this Reactor can be run without an extra executor
+  // scheduling. This should only be used for internally-defined reactors with
+  // trivial reactions.
+  virtual bool InternalInlineable() { return false; }
+
+ private:
+  template <class Request, class Response>
+  friend class CallbackUnaryHandler;
+  template <class Request, class Response>
+  friend class CallbackClientStreamingHandler;
+  template <class Request, class Response>
+  friend class CallbackServerStreamingHandler;
+  template <class Request, class Response>
+  friend class CallbackBidiHandler;
+};
+
+/// The base class of ServerCallbackUnary etc.
+class ServerCallbackCall {
+ public:
+  virtual ~ServerCallbackCall() {}
+
+  // This object is responsible for tracking when it is safe to call OnDone and
+  // OnCancel. OnDone should not be called until the method handler is complete,
+  // Finish has been called, the ServerContext CompletionOp (which tracks
+  // cancellation or successful completion) has completed, and all outstanding
+  // Read/Write actions have seen their reactions. OnCancel should not be called
+  // until after the method handler is done and the RPC has completed with a
+  // cancellation. This is tracked by counting how many of these conditions have
+  // been met and calling OnCancel when none remain unmet.
+
+  // Public versions of MaybeDone: one where we don't know the reactor in
+  // advance (used for the ServerContext CompletionOp), and one for where we
+  // know the inlineability of the OnDone reaction. You should set the inline
+  // flag to true if either the Reactor is InternalInlineable() or if this
+  // callback is already being forced to run dispatched to an executor
+  // (typically because it contains additional work than just the MaybeDone).
+
+  void MaybeDone() {
+    if (GPR_UNLIKELY(Unref() == 1)) {
+      ScheduleOnDone(reactor()->InternalInlineable());
+    }
+  }
+
+  void MaybeDone(bool inline_ondone) {
+    if (GPR_UNLIKELY(Unref() == 1)) {
+      ScheduleOnDone(inline_ondone);
+    }
+  }
+
+  // Fast version called with known reactor passed in, used from derived
+  // classes, typically in non-cancel case
+  void MaybeCallOnCancel(ServerReactor* reactor) {
+    if (GPR_UNLIKELY(UnblockCancellation())) {
+      CallOnCancel(reactor);
+    }
+  }
+
+  // Slower version called from object that doesn't know the reactor a priori
+  // (such as the ServerContext CompletionOp which is formed before the
+  // reactor). This is used in cancel cases only, so it's ok to be slower and
+  // invoke a virtual function.
+  void MaybeCallOnCancel() {
+    if (GPR_UNLIKELY(UnblockCancellation())) {
+      CallOnCancel(reactor());
+    }
+  }
+
+ protected:
+  /// Increases the reference count
+  void Ref() { callbacks_outstanding_.fetch_add(1, std::memory_order_relaxed); }
+
+ private:
+  virtual ServerReactor* reactor() = 0;
+
+  // CallOnDone performs the work required at completion of the RPC: invoking
+  // the OnDone function and doing all necessary cleanup. This function is only
+  // ever invoked on a fully-Unref'fed ServerCallbackCall.
+  virtual void CallOnDone() = 0;
+
+  // If the OnDone reaction is inlineable, execute it inline. Otherwise send it
+  // to an executor.
+  void ScheduleOnDone(bool inline_ondone);
+
+  // If the OnCancel reaction is inlineable, execute it inline. Otherwise send
+  // it to an executor.
+  void CallOnCancel(ServerReactor* reactor);
+
+  // Implement the cancellation constraint counter. Return true if OnCancel
+  // should be called, false otherwise.
+  bool UnblockCancellation() {
+    return on_cancel_conditions_remaining_.fetch_sub(
+               1, std::memory_order_acq_rel) == 1;
+  }
+
+  /// Decreases the reference count and returns the previous value
+  int Unref() {
+    return callbacks_outstanding_.fetch_sub(1, std::memory_order_acq_rel);
+  }
+
+  std::atomic_int on_cancel_conditions_remaining_{2};
+  std::atomic_int callbacks_outstanding_{
+      3};  // reserve for start, Finish, and CompletionOp
+};
+
+template <class Request, class Response>
+class DefaultMessageHolder : public MessageHolder<Request, Response> {
+ public:
+  DefaultMessageHolder() {
+    this->set_request(&request_obj_);
+    this->set_response(&response_obj_);
+  }
+  void Release() override {
+    // the object is allocated in the call arena.
+    this->~DefaultMessageHolder<Request, Response>();
+  }
+
+ private:
+  Request request_obj_;
+  Response response_obj_;
+};
+
+}  // namespace internal
+
+// Forward declarations
+class ServerUnaryReactor;
+template <class Request>
+class ServerReadReactor;
+template <class Response>
+class ServerWriteReactor;
+template <class Request, class Response>
+class ServerBidiReactor;
+
+// NOTE: The actual call/stream object classes are provided as API only to
+// support mocking. There are no implementations of these class interfaces in
+// the API.
+class ServerCallbackUnary : public internal::ServerCallbackCall {
+ public:
+  ~ServerCallbackUnary() override {}
+  virtual void Finish(grpc::Status s) = 0;
+  virtual void SendInitialMetadata() = 0;
+
+ protected:
+  // Use a template rather than explicitly specifying ServerUnaryReactor to
+  // delay binding and avoid a circular forward declaration issue
+  template <class Reactor>
+  void BindReactor(Reactor* reactor) {
+    reactor->InternalBindCall(this);
+  }
+};
+
+template <class Request>
+class ServerCallbackReader : public internal::ServerCallbackCall {
+ public:
+  ~ServerCallbackReader() override {}
+  virtual void Finish(grpc::Status s) = 0;
+  virtual void SendInitialMetadata() = 0;
+  virtual void Read(Request* msg) = 0;
+
+ protected:
+  void BindReactor(ServerReadReactor<Request>* reactor) {
+    reactor->InternalBindReader(this);
+  }
+};
+
+template <class Response>
+class ServerCallbackWriter : public internal::ServerCallbackCall {
+ public:
+  ~ServerCallbackWriter() override {}
+
+  virtual void Finish(grpc::Status s) = 0;
+  virtual void SendInitialMetadata() = 0;
+  virtual void Write(const Response* msg, grpc::WriteOptions options) = 0;
+  virtual void WriteAndFinish(const Response* msg, grpc::WriteOptions options,
+                              grpc::Status s) = 0;
+
+ protected:
+  void BindReactor(ServerWriteReactor<Response>* reactor) {
+    reactor->InternalBindWriter(this);
+  }
+};
+
+template <class Request, class Response>
+class ServerCallbackReaderWriter : public internal::ServerCallbackCall {
+ public:
+  ~ServerCallbackReaderWriter() override {}
+
+  virtual void Finish(grpc::Status s) = 0;
+  virtual void SendInitialMetadata() = 0;
+  virtual void Read(Request* msg) = 0;
+  virtual void Write(const Response* msg, grpc::WriteOptions options) = 0;
+  virtual void WriteAndFinish(const Response* msg, grpc::WriteOptions options,
+                              grpc::Status s) = 0;
+
+ protected:
+  void BindReactor(ServerBidiReactor<Request, Response>* reactor) {
+    reactor->InternalBindStream(this);
+  }
+};
+
+// The following classes are the reactor interfaces that are to be implemented
+// by the user, returned as the output parameter of the method handler for a
+// callback method. Note that none of the classes are pure; all reactions have a
+// default empty reaction so that the user class only needs to override those
+// reactions that it cares about. The reaction methods will be invoked by the
+// library in response to the completion of various operations. Reactions must
+// not include blocking operations (such as blocking I/O, starting synchronous
+// RPCs, or waiting on condition variables). Reactions may be invoked
+// concurrently, except that OnDone is called after all others (assuming proper
+// API usage). The reactor may not be deleted until OnDone is called.
+
+/// \a ServerBidiReactor is the interface for a bidirectional streaming RPC.
+template <class Request, class Response>
+class ServerBidiReactor : public internal::ServerReactor {
+ public:
+  // NOTE: Initializing stream_ as a constructor initializer rather than a
+  //       default initializer because gcc-4.x requires a copy constructor for
+  //       default initializing a templated member, which isn't ok for atomic.
+  // TODO(vjpai): Switch to default constructor and default initializer when
+  //              gcc-4.x is no longer supported
+  ServerBidiReactor() : stream_(nullptr) {}
+  ~ServerBidiReactor() override = default;
+
+  /// Send any initial metadata stored in the RPC context. If not invoked,
+  /// any initial metadata will be passed along with the first Write or the
+  /// Finish (if there are no writes).
+  void StartSendInitialMetadata() Y_ABSL_LOCKS_EXCLUDED(stream_mu_) {
+    ServerCallbackReaderWriter<Request, Response>* stream =
+        stream_.load(std::memory_order_acquire);
+    if (stream == nullptr) {
+      grpc::internal::MutexLock l(&stream_mu_);
+      stream = stream_.load(std::memory_order_relaxed);
+      if (stream == nullptr) {
+        backlog_.send_initial_metadata_wanted = true;
+        return;
+      }
+    }
+    stream->SendInitialMetadata();
+  }
+
+  /// Initiate a read operation.
+  ///
+  /// \param[out] req Where to eventually store the read message. Valid when
+  ///                 the library calls OnReadDone
+  void StartRead(Request* req) Y_ABSL_LOCKS_EXCLUDED(stream_mu_) {
+    ServerCallbackReaderWriter<Request, Response>* stream =
+        stream_.load(std::memory_order_acquire);
+    if (stream == nullptr) {
+      grpc::internal::MutexLock l(&stream_mu_);
+      stream = stream_.load(std::memory_order_relaxed);
+      if (stream == nullptr) {
+        backlog_.read_wanted = req;
+        return;
+      }
+    }
+    stream->Read(req);
+  }
+
+  /// Initiate a write operation.
+  ///
+  /// \param[in] resp The message to be written. The library does not take
+  ///                 ownership but the caller must ensure that the message is
+  ///                 not deleted or modified until OnWriteDone is called.
+  void StartWrite(const Response* resp) {
+    StartWrite(resp, grpc::WriteOptions());
+  }
+
+  /// Initiate a write operation with specified options.
+  ///
+  /// \param[in] resp The message to be written. The library does not take
+  ///                 ownership but the caller must ensure that the message is
+  ///                 not deleted or modified until OnWriteDone is called.
+  /// \param[in] options The WriteOptions to use for writing this message
+  void StartWrite(const Response* resp, grpc::WriteOptions options)
+      Y_ABSL_LOCKS_EXCLUDED(stream_mu_) {
+    ServerCallbackReaderWriter<Request, Response>* stream =
+        stream_.load(std::memory_order_acquire);
+    if (stream == nullptr) {
+      grpc::internal::MutexLock l(&stream_mu_);
+      stream = stream_.load(std::memory_order_relaxed);
+      if (stream == nullptr) {
+        backlog_.write_wanted = resp;
+        backlog_.write_options_wanted = options;
+        return;
+      }
+    }
+    stream->Write(resp, options);
+  }
+
+  /// Initiate a write operation with specified options and final RPC Status,
+  /// which also causes any trailing metadata for this RPC to be sent out.
+  /// StartWriteAndFinish is like merging StartWriteLast and Finish into a
+  /// single step. A key difference, though, is that this operation doesn't have
+  /// an OnWriteDone reaction - it is considered complete only when OnDone is
+  /// available. An RPC can either have StartWriteAndFinish or Finish, but not
+  /// both.
+  ///
+  /// \param[in] resp The message to be written. The library does not take
+  ///                 ownership but the caller must ensure that the message is
+  ///                 not deleted or modified until OnDone is called.
+  /// \param[in] options The WriteOptions to use for writing this message
+  /// \param[in] s The status outcome of this RPC
+  void StartWriteAndFinish(const Response* resp, grpc::WriteOptions options,
+                           grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(stream_mu_) {
+    ServerCallbackReaderWriter<Request, Response>* stream =
+        stream_.load(std::memory_order_acquire);
+    if (stream == nullptr) {
+      grpc::internal::MutexLock l(&stream_mu_);
+      stream = stream_.load(std::memory_order_relaxed);
+      if (stream == nullptr) {
+        backlog_.write_and_finish_wanted = true;
+        backlog_.write_wanted = resp;
+        backlog_.write_options_wanted = options;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    stream->WriteAndFinish(resp, options, std::move(s));
+  }
+
+  /// Inform system of a planned write operation with specified options, but
+  /// allow the library to schedule the actual write coalesced with the writing
+  /// of trailing metadata (which takes place on a Finish call).
+  ///
+  /// \param[in] resp The message to be written. The library does not take
+  ///                 ownership but the caller must ensure that the message is
+  ///                 not deleted or modified until OnWriteDone is called.
+  /// \param[in] options The WriteOptions to use for writing this message
+  void StartWriteLast(const Response* resp, grpc::WriteOptions options) {
+    StartWrite(resp, options.set_last_message());
+  }
+
+  /// Indicate that the stream is to be finished and the trailing metadata and
+  /// RPC status are to be sent. Every RPC MUST be finished using either Finish
+  /// or StartWriteAndFinish (but not both), even if the RPC is already
+  /// cancelled.
+  ///
+  /// \param[in] s The status outcome of this RPC
+  void Finish(grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(stream_mu_) {
+    ServerCallbackReaderWriter<Request, Response>* stream =
+        stream_.load(std::memory_order_acquire);
+    if (stream == nullptr) {
+      grpc::internal::MutexLock l(&stream_mu_);
+      stream = stream_.load(std::memory_order_relaxed);
+      if (stream == nullptr) {
+        backlog_.finish_wanted = true;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    stream->Finish(std::move(s));
+  }
+
+  /// Notifies the application that an explicit StartSendInitialMetadata
+  /// operation completed. Not used when the sending of initial metadata
+  /// piggybacks onto the first write.
+  ///
+  /// \param[in] ok Was it successful? If false, no further write-side operation
+  ///               will succeed.
+  virtual void OnSendInitialMetadataDone(bool /*ok*/) {}
+
+  /// Notifies the application that a StartRead operation completed.
+  ///
+  /// \param[in] ok Was it successful? If false, no further read-side operation
+  ///               will succeed.
+  virtual void OnReadDone(bool /*ok*/) {}
+
+  /// Notifies the application that a StartWrite (or StartWriteLast) operation
+  /// completed.
+  ///
+  /// \param[in] ok Was it successful? If false, no further write-side operation
+  ///               will succeed.
+  virtual void OnWriteDone(bool /*ok*/) {}
+
+  /// Notifies the application that all operations associated with this RPC
+  /// have completed. This is an override (from the internal base class) but
+  /// still abstract, so derived classes MUST override it to be instantiated.
+  void OnDone() override = 0;
+
+  /// Notifies the application that this RPC has been cancelled. This is an
+  /// override (from the internal base class) but not final, so derived classes
+  /// should override it if they want to take action.
+  void OnCancel() override {}
+
+ private:
+  friend class ServerCallbackReaderWriter<Request, Response>;
+  // May be overridden by internal implementation details. This is not a public
+  // customization point.
+  virtual void InternalBindStream(
+      ServerCallbackReaderWriter<Request, Response>* stream) {
+    grpc::internal::MutexLock l(&stream_mu_);
+
+    if (GPR_UNLIKELY(backlog_.send_initial_metadata_wanted)) {
+      stream->SendInitialMetadata();
+    }
+    if (GPR_UNLIKELY(backlog_.read_wanted != nullptr)) {
+      stream->Read(backlog_.read_wanted);
+    }
+    if (GPR_UNLIKELY(backlog_.write_and_finish_wanted)) {
+      stream->WriteAndFinish(backlog_.write_wanted,
+                             std::move(backlog_.write_options_wanted),
+                             std::move(backlog_.status_wanted));
+    } else {
+      if (GPR_UNLIKELY(backlog_.write_wanted != nullptr)) {
+        stream->Write(backlog_.write_wanted,
+                      std::move(backlog_.write_options_wanted));
+      }
+      if (GPR_UNLIKELY(backlog_.finish_wanted)) {
+        stream->Finish(std::move(backlog_.status_wanted));
+      }
+    }
+    // Set stream_ last so that other functions can use it lock-free
+    stream_.store(stream, std::memory_order_release);
+  }
+
+  grpc::internal::Mutex stream_mu_;
+  // TODO(vjpai): Make stream_or_backlog_ into a std::variant or y_absl::variant
+  //              once C++17 or ABSL is supported since stream and backlog are
+  //              mutually exclusive in this class. Do likewise with the
+  //              remaining reactor classes and their backlogs as well.
+  std::atomic<ServerCallbackReaderWriter<Request, Response>*> stream_{nullptr};
+  struct PreBindBacklog {
+    bool send_initial_metadata_wanted = false;
+    bool write_and_finish_wanted = false;
+    bool finish_wanted = false;
+    Request* read_wanted = nullptr;
+    const Response* write_wanted = nullptr;
+    grpc::WriteOptions write_options_wanted;
+    grpc::Status status_wanted;
+  };
+  PreBindBacklog backlog_ Y_ABSL_GUARDED_BY(stream_mu_);
+};
+
+/// \a ServerReadReactor is the interface for a client-streaming RPC.
+template <class Request>
+class ServerReadReactor : public internal::ServerReactor {
+ public:
+  ServerReadReactor() : reader_(nullptr) {}
+  ~ServerReadReactor() override = default;
+
+  /// The following operation initiations are exactly like ServerBidiReactor.
+  void StartSendInitialMetadata() Y_ABSL_LOCKS_EXCLUDED(reader_mu_) {
+    ServerCallbackReader<Request>* reader =
+        reader_.load(std::memory_order_acquire);
+    if (reader == nullptr) {
+      grpc::internal::MutexLock l(&reader_mu_);
+      reader = reader_.load(std::memory_order_relaxed);
+      if (reader == nullptr) {
+        backlog_.send_initial_metadata_wanted = true;
+        return;
+      }
+    }
+    reader->SendInitialMetadata();
+  }
+  void StartRead(Request* req) Y_ABSL_LOCKS_EXCLUDED(reader_mu_) {
+    ServerCallbackReader<Request>* reader =
+        reader_.load(std::memory_order_acquire);
+    if (reader == nullptr) {
+      grpc::internal::MutexLock l(&reader_mu_);
+      reader = reader_.load(std::memory_order_relaxed);
+      if (reader == nullptr) {
+        backlog_.read_wanted = req;
+        return;
+      }
+    }
+    reader->Read(req);
+  }
+  void Finish(grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(reader_mu_) {
+    ServerCallbackReader<Request>* reader =
+        reader_.load(std::memory_order_acquire);
+    if (reader == nullptr) {
+      grpc::internal::MutexLock l(&reader_mu_);
+      reader = reader_.load(std::memory_order_relaxed);
+      if (reader == nullptr) {
+        backlog_.finish_wanted = true;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    reader->Finish(std::move(s));
+  }
+
+  /// The following notifications are exactly like ServerBidiReactor.
+  virtual void OnSendInitialMetadataDone(bool /*ok*/) {}
+  virtual void OnReadDone(bool /*ok*/) {}
+  void OnDone() override = 0;
+  void OnCancel() override {}
+
+ private:
+  friend class ServerCallbackReader<Request>;
+
+  // May be overridden by internal implementation details. This is not a public
+  // customization point.
+  virtual void InternalBindReader(ServerCallbackReader<Request>* reader)
+      Y_ABSL_LOCKS_EXCLUDED(reader_mu_) {
+    grpc::internal::MutexLock l(&reader_mu_);
+
+    if (GPR_UNLIKELY(backlog_.send_initial_metadata_wanted)) {
+      reader->SendInitialMetadata();
+    }
+    if (GPR_UNLIKELY(backlog_.read_wanted != nullptr)) {
+      reader->Read(backlog_.read_wanted);
+    }
+    if (GPR_UNLIKELY(backlog_.finish_wanted)) {
+      reader->Finish(std::move(backlog_.status_wanted));
+    }
+    // Set reader_ last so that other functions can use it lock-free
+    reader_.store(reader, std::memory_order_release);
+  }
+
+  grpc::internal::Mutex reader_mu_;
+  std::atomic<ServerCallbackReader<Request>*> reader_{nullptr};
+  struct PreBindBacklog {
+    bool send_initial_metadata_wanted = false;
+    bool finish_wanted = false;
+    Request* read_wanted = nullptr;
+    grpc::Status status_wanted;
+  };
+  PreBindBacklog backlog_ Y_ABSL_GUARDED_BY(reader_mu_);
+};
+
+/// \a ServerWriteReactor is the interface for a server-streaming RPC.
+template <class Response>
+class ServerWriteReactor : public internal::ServerReactor {
+ public:
+  ServerWriteReactor() : writer_(nullptr) {}
+  ~ServerWriteReactor() override = default;
+
+  /// The following operation initiations are exactly like ServerBidiReactor.
+  void StartSendInitialMetadata() Y_ABSL_LOCKS_EXCLUDED(writer_mu_) {
+    ServerCallbackWriter<Response>* writer =
+        writer_.load(std::memory_order_acquire);
+    if (writer == nullptr) {
+      grpc::internal::MutexLock l(&writer_mu_);
+      writer = writer_.load(std::memory_order_relaxed);
+      if (writer == nullptr) {
+        backlog_.send_initial_metadata_wanted = true;
+        return;
+      }
+    }
+    writer->SendInitialMetadata();
+  }
+  void StartWrite(const Response* resp) {
+    StartWrite(resp, grpc::WriteOptions());
+  }
+  void StartWrite(const Response* resp, grpc::WriteOptions options)
+      Y_ABSL_LOCKS_EXCLUDED(writer_mu_) {
+    ServerCallbackWriter<Response>* writer =
+        writer_.load(std::memory_order_acquire);
+    if (writer == nullptr) {
+      grpc::internal::MutexLock l(&writer_mu_);
+      writer = writer_.load(std::memory_order_relaxed);
+      if (writer == nullptr) {
+        backlog_.write_wanted = resp;
+        backlog_.write_options_wanted = options;
+        return;
+      }
+    }
+    writer->Write(resp, options);
+  }
+  void StartWriteAndFinish(const Response* resp, grpc::WriteOptions options,
+                           grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(writer_mu_) {
+    ServerCallbackWriter<Response>* writer =
+        writer_.load(std::memory_order_acquire);
+    if (writer == nullptr) {
+      grpc::internal::MutexLock l(&writer_mu_);
+      writer = writer_.load(std::memory_order_relaxed);
+      if (writer == nullptr) {
+        backlog_.write_and_finish_wanted = true;
+        backlog_.write_wanted = resp;
+        backlog_.write_options_wanted = options;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    writer->WriteAndFinish(resp, options, std::move(s));
+  }
+  void StartWriteLast(const Response* resp, grpc::WriteOptions options) {
+    StartWrite(resp, options.set_last_message());
+  }
+  void Finish(grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(writer_mu_) {
+    ServerCallbackWriter<Response>* writer =
+        writer_.load(std::memory_order_acquire);
+    if (writer == nullptr) {
+      grpc::internal::MutexLock l(&writer_mu_);
+      writer = writer_.load(std::memory_order_relaxed);
+      if (writer == nullptr) {
+        backlog_.finish_wanted = true;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    writer->Finish(std::move(s));
+  }
+
+  /// The following notifications are exactly like ServerBidiReactor.
+  virtual void OnSendInitialMetadataDone(bool /*ok*/) {}
+  virtual void OnWriteDone(bool /*ok*/) {}
+  void OnDone() override = 0;
+  void OnCancel() override {}
+
+ private:
+  friend class ServerCallbackWriter<Response>;
+  // May be overridden by internal implementation details. This is not a public
+  // customization point.
+  virtual void InternalBindWriter(ServerCallbackWriter<Response>* writer)
+      Y_ABSL_LOCKS_EXCLUDED(writer_mu_) {
+    grpc::internal::MutexLock l(&writer_mu_);
+
+    if (GPR_UNLIKELY(backlog_.send_initial_metadata_wanted)) {
+      writer->SendInitialMetadata();
+    }
+    if (GPR_UNLIKELY(backlog_.write_and_finish_wanted)) {
+      writer->WriteAndFinish(backlog_.write_wanted,
+                             std::move(backlog_.write_options_wanted),
+                             std::move(backlog_.status_wanted));
+    } else {
+      if (GPR_UNLIKELY(backlog_.write_wanted != nullptr)) {
+        writer->Write(backlog_.write_wanted,
+                      std::move(backlog_.write_options_wanted));
+      }
+      if (GPR_UNLIKELY(backlog_.finish_wanted)) {
+        writer->Finish(std::move(backlog_.status_wanted));
+      }
+    }
+    // Set writer_ last so that other functions can use it lock-free
+    writer_.store(writer, std::memory_order_release);
+  }
+
+  grpc::internal::Mutex writer_mu_;
+  std::atomic<ServerCallbackWriter<Response>*> writer_{nullptr};
+  struct PreBindBacklog {
+    bool send_initial_metadata_wanted = false;
+    bool write_and_finish_wanted = false;
+    bool finish_wanted = false;
+    const Response* write_wanted = nullptr;
+    grpc::WriteOptions write_options_wanted;
+    grpc::Status status_wanted;
+  };
+  PreBindBacklog backlog_ Y_ABSL_GUARDED_BY(writer_mu_);
+};
+
+class ServerUnaryReactor : public internal::ServerReactor {
+ public:
+  ServerUnaryReactor() : call_(nullptr) {}
+  ~ServerUnaryReactor() override = default;
+
+  /// StartSendInitialMetadata is exactly like ServerBidiReactor.
+  void StartSendInitialMetadata() Y_ABSL_LOCKS_EXCLUDED(call_mu_) {
+    ServerCallbackUnary* call = call_.load(std::memory_order_acquire);
+    if (call == nullptr) {
+      grpc::internal::MutexLock l(&call_mu_);
+      call = call_.load(std::memory_order_relaxed);
+      if (call == nullptr) {
+        backlog_.send_initial_metadata_wanted = true;
+        return;
+      }
+    }
+    call->SendInitialMetadata();
+  }
+  /// Finish is similar to ServerBidiReactor except for one detail.
+  /// If the status is non-OK, any message will not be sent. Instead,
+  /// the client will only receive the status and any trailing metadata.
+  void Finish(grpc::Status s) Y_ABSL_LOCKS_EXCLUDED(call_mu_) {
+    ServerCallbackUnary* call = call_.load(std::memory_order_acquire);
+    if (call == nullptr) {
+      grpc::internal::MutexLock l(&call_mu_);
+      call = call_.load(std::memory_order_relaxed);
+      if (call == nullptr) {
+        backlog_.finish_wanted = true;
+        backlog_.status_wanted = std::move(s);
+        return;
+      }
+    }
+    call->Finish(std::move(s));
+  }
+
+  /// The following notifications are exactly like ServerBidiReactor.
+  virtual void OnSendInitialMetadataDone(bool /*ok*/) {}
+  void OnDone() override = 0;
+  void OnCancel() override {}
+
+ private:
+  friend class ServerCallbackUnary;
+  // May be overridden by internal implementation details. This is not a public
+  // customization point.
+  virtual void InternalBindCall(ServerCallbackUnary* call)
+      Y_ABSL_LOCKS_EXCLUDED(call_mu_) {
+    grpc::internal::MutexLock l(&call_mu_);
+
+    if (GPR_UNLIKELY(backlog_.send_initial_metadata_wanted)) {
+      call->SendInitialMetadata();
+    }
+    if (GPR_UNLIKELY(backlog_.finish_wanted)) {
+      call->Finish(std::move(backlog_.status_wanted));
+    }
+    // Set call_ last so that other functions can use it lock-free
+    call_.store(call, std::memory_order_release);
+  }
+
+  grpc::internal::Mutex call_mu_;
+  std::atomic<ServerCallbackUnary*> call_{nullptr};
+  struct PreBindBacklog {
+    bool send_initial_metadata_wanted = false;
+    bool finish_wanted = false;
+    grpc::Status status_wanted;
+  };
+  PreBindBacklog backlog_ Y_ABSL_GUARDED_BY(call_mu_);
+};
+
+namespace internal {
+
+template <class Base>
+class FinishOnlyReactor : public Base {
+ public:
+  explicit FinishOnlyReactor(grpc::Status s) { this->Finish(std::move(s)); }
+  void OnDone() override { this->~FinishOnlyReactor(); }
+};
+
+using UnimplementedUnaryReactor = FinishOnlyReactor<ServerUnaryReactor>;
+template <class Request>
+using UnimplementedReadReactor = FinishOnlyReactor<ServerReadReactor<Request>>;
+template <class Response>
+using UnimplementedWriteReactor =
+    FinishOnlyReactor<ServerWriteReactor<Response>>;
+template <class Request, class Response>
+using UnimplementedBidiReactor =
+    FinishOnlyReactor<ServerBidiReactor<Request, Response>>;
+
+}  // namespace internal
+
+// TODO(vjpai): Remove namespace experimental when last known users are migrated
+// off.
+namespace experimental {
+
+template <class Request, class Response>
+using ServerBidiReactor = ::grpc::ServerBidiReactor<Request, Response>;
+
+}  // namespace experimental
+
+}  // namespace grpc
 
 #endif  // GRPCPP_SUPPORT_SERVER_CALLBACK_H