tdlight/tdactor/td/actor/PromiseFuture.h

//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once

#include "td/actor/actor.h"

#include "td/utils/Closure.h"
#include "td/utils/common.h"
#include "td/utils/invoke.h"  // for tuple_for_each
#include "td/utils/logging.h"
#include "td/utils/ScopeGuard.h"
#include "td/utils/Status.h"

#include <atomic>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>

namespace td {

template <class T = Unit>
class PromiseInterface {
 public:
  PromiseInterface() = default;
  PromiseInterface(const PromiseInterface &) = delete;
  PromiseInterface &operator=(const PromiseInterface &) = delete;
  PromiseInterface(PromiseInterface &&) = default;
  PromiseInterface &operator=(PromiseInterface &&) = default;
  virtual ~PromiseInterface() = default;
  virtual void set_value(T &&value) {
    set_result(std::move(value));
  }
  virtual void set_error(Status &&error) {
    set_result(std::move(error));
  }
  virtual void set_result(Result<T> &&result) {
    if (result.is_ok()) {
      set_value(result.move_as_ok());
    } else {
      set_error(result.move_as_error());
    }
  }
  virtual bool is_cancellable() const {
    return false;
  }
  virtual bool is_cancelled() const {
    return false;
  }

  virtual void start_migrate(int32 sched_id) {
  }
  virtual void finish_migrate() {
  }
};

template <class T = Unit>
class FutureInterface {
 public:
  FutureInterface() = default;
  FutureInterface(const FutureInterface &) = delete;
  FutureInterface &operator=(const FutureInterface &) = delete;
  FutureInterface(FutureInterface &&) = default;
  FutureInterface &operator=(FutureInterface &&) = default;
  virtual ~FutureInterface() = default;
  virtual bool is_ready() = 0;
  virtual bool is_ok() = 0;
  virtual bool is_error() = 0;
  virtual const T &ok() = 0;
  virtual T move_as_ok() = 0;
  virtual const Status &error() = 0;
  virtual Status move_as_error() TD_WARN_UNUSED_RESULT = 0;
  virtual const Result<T> &result() = 0;
  virtual Result<T> move_as_result() TD_WARN_UNUSED_RESULT = 0;
};

template <class T>
class SafePromise;

template <class T = Unit>
class Promise {
 public:
  void set_value(T &&value) {
    if (!promise_) {
      return;
    }
    promise_->set_value(std::move(value));
    promise_.reset();
  }
  void set_error(Status &&error) {
    if (!promise_) {
      return;
    }
    promise_->set_error(std::move(error));
    promise_.reset();
  }
  void set_result(Result<T> &&result) {
    if (!promise_) {
      return;
    }
    promise_->set_result(std::move(result));
    promise_.reset();
  }
  void reset() {
    promise_.reset();
  }
  void start_migrate(int32 sched_id) {
    if (!promise_) {
      return;
    }
    promise_->start_migrate(sched_id);
  }
  void finish_migrate() {
    if (!promise_) {
      return;
    }
    promise_->finish_migrate();
  }
  bool is_cancellable() const {
    if (!promise_) {
      return false;
    }
    return promise_->is_cancellable();
  }
  bool is_cancelled() const {
    if (!promise_) {
      return false;
    }
    return promise_->is_cancelled();
  }
  std::unique_ptr<PromiseInterface<T>> release() {
    return std::move(promise_);
  }

  Promise() = default;
  explicit Promise(std::unique_ptr<PromiseInterface<T>> promise) : promise_(std::move(promise)) {
  }
  Promise(SafePromise<T> &&other);
  Promise &operator=(SafePromise<T> &&other);

  explicit operator bool() {
    return static_cast<bool>(promise_);
  }

 private:
  std::unique_ptr<PromiseInterface<T>> promise_;
};

template <class T>
void start_migrate(Promise<T> &promise, int32 sched_id) {
  // promise.start_migrate(sched_id);
}
template <class T>
void finish_migrate(Promise<T> &promise) {
  // promise.finish_migrate();
}

template <class T = Unit>
class SafePromise {
 public:
  SafePromise(Promise<T> promise, Result<T> result) : promise_(std::move(promise)), result_(std::move(result)) {
  }
  SafePromise(const SafePromise &other) = delete;
  SafePromise &operator=(const SafePromise &other) = delete;
  SafePromise(SafePromise &&other) = default;
  SafePromise &operator=(SafePromise &&other) = default;
  ~SafePromise() {
    if (promise_) {
      promise_.set_result(std::move(result_));
    }
  }
  Promise<T> release() {
    return std::move(promise_);
  }

 private:
  Promise<T> promise_;
  Result<T> result_;
};

template <class T>
Promise<T>::Promise(SafePromise<T> &&other) : Promise(other.release()) {
}
template <class T>
Promise<T> &Promise<T>::operator=(SafePromise<T> &&other) {
  *this = other.release();
  return *this;
}

class CancellationToken {
 public:
  explicit CancellationToken(bool init = false) {
    if (init) {
      ptr_ = std::make_shared<std::atomic<bool>>(false);
    }
  }
  CancellationToken(const CancellationToken &other) = default;
  CancellationToken &operator=(const CancellationToken &other) {
    cancel();
    ptr_ = other.ptr_;
    return *this;
  }
  CancellationToken(CancellationToken &&other) = default;
  CancellationToken &operator=(CancellationToken &&other) {
    cancel();
    ptr_ = std::move(other.ptr_);
    return *this;
  }
  ~CancellationToken() {
    cancel();
  }
  bool is_canceled() const {
    return !ptr_ || *ptr_;
  }
  void cancel() {
    if (ptr_) {
      ptr_->store(true, std::memory_order_relaxed);
      ptr_.reset();
    }
  }

 private:
  std::shared_ptr<std::atomic<bool>> ptr_;
};

namespace detail {

class EventPromise : public PromiseInterface<Unit> {
 public:
  void set_value(Unit &&) override {
    ok_.try_emit();
    fail_.clear();
  }
  void set_error(Status &&) override {
    do_set_error();
  }

  EventPromise(const EventPromise &other) = delete;
  EventPromise &operator=(const EventPromise &other) = delete;
  EventPromise(EventPromise &&other) = delete;
  EventPromise &operator=(EventPromise &&other) = delete;
  ~EventPromise() override {
    do_set_error();
  }

  EventPromise() = default;
  explicit EventPromise(EventFull ok) : ok_(std::move(ok)), use_ok_as_fail_(true) {
  }
  EventPromise(EventFull ok, EventFull fail) : ok_(std::move(ok)), fail_(std::move(fail)), use_ok_as_fail_(false) {
  }

 private:
  EventFull ok_;
  EventFull fail_;
  bool use_ok_as_fail_ = false;
  void do_set_error() {
    if (use_ok_as_fail_) {
      ok_.try_emit();
    } else {
      ok_.clear();
      fail_.try_emit();
    }
  }
};

template <typename T>
struct GetArg : public GetArg<decltype(&T::operator())> {};

template <class C, class R, class Arg>
class GetArg<R (C::*)(Arg)> {
 public:
  using type = Arg;
};
template <class C, class R, class Arg>
class GetArg<R (C::*)(Arg) const> {
 public:
  using type = Arg;
};

template <class T>
using get_arg_t = std::decay_t<typename GetArg<T>::type>;

template <class T>
struct DropResult {
  using type = T;
};

template <class T>
struct DropResult<Result<T>> {
  using type = T;
};

template <class T>
using drop_result_t = typename DropResult<T>::type;

template <class PromiseT>
class CancellablePromise : public PromiseT {
 public:
  template <class... ArgsT>
  CancellablePromise(CancellationToken cancellation_token, ArgsT &&... args)
      : PromiseT(std::forward<ArgsT>(args)...), cancellation_token_(std::move(cancellation_token)) {
  }
  virtual bool is_cancellable() const {
    return true;
  }
  virtual bool is_cancelled() const {
    return cancellation_token_.is_canceled();
  }

 private:
  CancellationToken cancellation_token_;
};

template <class ValueT, class FunctionOkT, class FunctionFailT>
class LambdaPromise : public PromiseInterface<ValueT> {
  enum OnFail { None, Ok, Fail };

 public:
  void set_value(ValueT &&value) override {
    ok_(std::move(value));
    on_fail_ = None;
  }
  void set_error(Status &&error) override {
    do_error(std::move(error));
  }
  LambdaPromise(const LambdaPromise &other) = delete;
  LambdaPromise &operator=(const LambdaPromise &other) = delete;
  LambdaPromise(LambdaPromise &&other) = delete;
  LambdaPromise &operator=(LambdaPromise &&other) = delete;
  ~LambdaPromise() override {
    do_error(Status::Error("Lost promise"));
  }

  template <class FromOkT, class FromFailT>
  LambdaPromise(FromOkT &&ok, FromFailT &&fail, bool use_ok_as_fail)
      : ok_(std::forward<FromOkT>(ok)), fail_(std::forward<FromFailT>(fail)), on_fail_(use_ok_as_fail ? Ok : Fail) {
  }

 private:
  FunctionOkT ok_;
  FunctionFailT fail_;
  OnFail on_fail_ = None;

  template <class FuncT, class ArgT = detail::get_arg_t<FuncT>>
  std::enable_if_t<std::is_assignable<ArgT, Status>::value> do_error_impl(FuncT &func, Status &&status) {
    func(std::move(status));
  }

  template <class FuncT, class ArgT = detail::get_arg_t<FuncT>>
  std::enable_if_t<!std::is_assignable<ArgT, Status>::value> do_error_impl(FuncT &func, Status &&status) {
    func(Auto());
  }

  void do_error(Status &&error) {
    switch (on_fail_) {
      case None:
        break;
      case Ok:
        do_error_impl(ok_, std::move(error));
        break;
      case Fail:
        fail_(std::move(error));
        break;
    }
    on_fail_ = None;
  }
};

template <class... ArgsT>
class JoinPromise : public PromiseInterface<Unit> {
 public:
  explicit JoinPromise(ArgsT &&... arg) : promises_(std::forward<ArgsT>(arg)...) {
  }
  void set_value(Unit &&) override {
    tuple_for_each(promises_, [](auto &promise) { promise.set_value(Unit()); });
  }
  void set_error(Status &&error) override {
    tuple_for_each(promises_, [&error](auto &promise) { promise.set_error(error.clone()); });
  }

 private:
  std::tuple<std::decay_t<ArgsT>...> promises_;
};
}  // namespace detail

/*** FutureActor and PromiseActor ***/
template <class T>
class FutureActor;

template <class T>
class PromiseActor;

template <class T>
class ActorTraits<FutureActor<T>> {
 public:
  static constexpr bool is_lite = true;
};

template <class T>
class PromiseActor final : public PromiseInterface<T> {
  friend class FutureActor<T>;
  enum State { Waiting, Hangup };

 public:
  PromiseActor() = default;
  PromiseActor(const PromiseActor &other) = delete;
  PromiseActor &operator=(const PromiseActor &other) = delete;
  PromiseActor(PromiseActor &&) = default;
  PromiseActor &operator=(PromiseActor &&) = default;
  ~PromiseActor() override {
    close();
  }

  void set_value(T &&value) override;
  void set_error(Status &&error) override;

  void close() {
    future_id_.reset();
  }

  // NB: if true is returned no further events will be sent
  bool is_hangup() {
    if (state_ == State::Hangup) {
      return true;
    }
    if (!future_id_.is_alive()) {
      state_ = State::Hangup;
      future_id_.release();
      event_.clear();
      return true;
    }
    return false;
  }

  template <class S>
  friend void init_promise_future(PromiseActor<S> *promise, FutureActor<S> *future);

  bool empty_promise() {
    return future_id_.empty();
  }
  bool empty() {
    return future_id_.empty();
  }

 private:
  ActorOwn<FutureActor<T>> future_id_;
  EventFull event_;
  State state_;

  void init() {
    state_ = State::Waiting;
    event_.clear();
  }
};

template <class T>
class FutureActor final : public Actor {
  friend class PromiseActor<T>;
  enum State { Waiting, Ready };

 public:
  static constexpr int Hangup = 426487;

  FutureActor() = default;

  FutureActor(const FutureActor &other) = delete;
  FutureActor &operator=(const FutureActor &other) = delete;

  FutureActor(FutureActor &&other) = default;
  FutureActor &operator=(FutureActor &&other) = default;

  ~FutureActor() override = default;

  bool is_ok() const {
    return is_ready() && result_.is_ok();
  }
  bool is_error() const {
    CHECK(is_ready());
    return is_ready() && result_.is_error();
  }
  T move_as_ok() {
    return move_as_result().move_as_ok();
  }
  Status move_as_error() TD_WARN_UNUSED_RESULT {
    return move_as_result().move_as_error();
  }
  Result<T> move_as_result() TD_WARN_UNUSED_RESULT {
    CHECK(is_ready());
    SCOPE_EXIT {
      do_stop();
    };
    return std::move(result_);
  }
  bool is_ready() const {
    return !empty() && state_ == State::Ready;
  }

  void close() {
    event_.clear();
    result_.clear();
    do_stop();
  }

  void set_event(EventFull &&event) {
    CHECK(!empty());
    event_ = std::move(event);
    if (state_ != State::Waiting) {
      event_.try_emit_later();
    }
  }

  template <class S>
  friend void init_promise_future(PromiseActor<S> *promise, FutureActor<S> *future);

 private:
  EventFull event_;
  Result<T> result_ = Status::Error(500, "Empty FutureActor");
  State state_;

  void set_value(T &&value) {
    set_result(std::move(value));
  }

  void set_error(Status &&error) {
    set_result(std::move(error));
  }

  void set_result(Result<T> &&result) {
    CHECK(state_ == State::Waiting);
    result_ = std::move(result);
    state_ = State::Ready;

    event_.try_emit_later();
  }

  void hangup() override {
    set_error(Status::Error<Hangup>());
  }

  void start_up() override {
    // empty
  }

  void init() {
    CHECK(empty());
    state_ = State::Waiting;
    event_.clear();
  }
};

template <class T>
void PromiseActor<T>::set_value(T &&value) {
  if (state_ == State::Waiting && !future_id_.empty()) {
    send_closure(std::move(future_id_), &FutureActor<T>::set_value, std::move(value));
  }
}
template <class T>
void PromiseActor<T>::set_error(Status &&error) {
  if (state_ == State::Waiting && !future_id_.empty()) {
    send_closure(std::move(future_id_), &FutureActor<T>::set_error, std::move(error));
  }
}

template <class S>
void init_promise_future(PromiseActor<S> *promise, FutureActor<S> *future) {
  promise->init();
  future->init();
  promise->future_id_ = register_actor("FutureActor", future);

  CHECK(future->get_info() != nullptr);
}

template <class T>
class PromiseFuture {
 public:
  PromiseFuture() {
    init_promise_future(&promise_, &future_);
  }
  PromiseActor<T> &promise() {
    return promise_;
  }
  FutureActor<T> &future() {
    return future_;
  }
  PromiseActor<T> &&move_promise() {
    return std::move(promise_);
  }
  FutureActor<T> &&move_future() {
    return std::move(future_);
  }

 private:
  PromiseActor<T> promise_;
  FutureActor<T> future_;
};

template <class T, class ActorAT, class ActorBT, class ResultT, class... DestArgsT, class... ArgsT>
FutureActor<T> send_promise(ActorId<ActorAT> actor_id, Send::Flags flags,
                            ResultT (ActorBT::*func)(PromiseActor<T> &&, DestArgsT...), ArgsT &&... args) {
  PromiseFuture<T> pf;
  ::td::Scheduler::instance()->send_closure(
      std::move(actor_id), create_immediate_closure(func, pf.move_promise(), std::forward<ArgsT>(args)...), flags);
  return pf.move_future();
}

class PromiseCreator {
 public:
  struct Ignore {
    void operator()(Status &&error) {
      error.ignore();
    }
  };

  template <class OkT, class ArgT = detail::drop_result_t<detail::get_arg_t<OkT>>>
  static Promise<ArgT> lambda(OkT &&ok) {
    return Promise<ArgT>(std::make_unique<detail::LambdaPromise<ArgT, std::decay_t<OkT>, Ignore>>(std::forward<OkT>(ok),
                                                                                                  Ignore(), true));
  }

  template <class OkT, class FailT, class ArgT = detail::get_arg_t<OkT>>
  static Promise<ArgT> lambda(OkT &&ok, FailT &&fail) {
    return Promise<ArgT>(std::make_unique<detail::LambdaPromise<ArgT, std::decay_t<OkT>, std::decay_t<FailT>>>(
        std::forward<OkT>(ok), std::forward<FailT>(fail), false));
  }

  template <class OkT, class ArgT = detail::drop_result_t<detail::get_arg_t<OkT>>>
  static auto cancellable_lambda(CancellationToken cancellation_token, OkT &&ok) {
    return Promise<ArgT>(
        std::make_unique<detail::CancellablePromise<detail::LambdaPromise<ArgT, std::decay_t<OkT>, Ignore>>>(
            std::move(cancellation_token), std::forward<OkT>(ok), Ignore(), true));
  }

  static Promise<> event(EventFull &&ok) {
    return Promise<>(std::make_unique<detail::EventPromise>(std::move(ok)));
  }

  static Promise<> event(EventFull ok, EventFull fail) {
    return Promise<>(std::make_unique<detail::EventPromise>(std::move(ok), std::move(fail)));
  }

  template <class... ArgsT>
  static Promise<> join(ArgsT &&... args) {
    return Promise<>(std::make_unique<detail::JoinPromise<ArgsT...>>(std::forward<ArgsT>(args)...));
  }

  template <class T>
  static Promise<T> from_promise_actor(PromiseActor<T> &&from) {
    return Promise<T>(std::make_unique<PromiseActor<T>>(std::move(from)));
  }
};

}  // namespace td