Promise.h

Go to the documentation of this file.

/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.
 */
#pragma once

#include <folly/Try.h>
#include <folly/fibers/traits.h>
#include <folly/functional/Invoke.h>

namespace folly {
namespace fibers {

class Baton;

template <typename T, typename BatonT = Baton>
class Promise {
 public:
  typedef T value_type;
  typedef BatonT baton_type;

  ~Promise();

  // not copyable
  Promise(const Promise&) = delete;
  Promise& operator=(const Promise&) = delete;

  // movable
  Promise(Promise&&) noexcept;
  Promise& operator=(Promise&&);

  void setValue();

  template <class M>
  void setValue(M&& value);

  void setTry(folly::Try<T>&& t);

  template <class F>
  void setWith(F&& func);

  void setException(folly::exception_wrapper);

  template <class F>
  static value_type await(F&& func);

 private:
  Promise(folly::Try<T>& value, BatonT& baton);
  folly::Try<T>* value_;
  BatonT* baton_;

  void throwIfFulfilled() const;

  template <class F>
  typename std::enable_if<
      std::is_convertible<invoke_result_t<F>, T>::value &&
      !std::is_same<T, void>::value>::type
  fulfilHelper(F&& func);

  template <class F>
  typename std::enable_if<
      std::is_same<invoke_result_t<F>, void>::value &&
      std::is_same<T, void>::value>::type
  fulfilHelper(F&& func);
};
} // namespace fibers
} // namespace folly

#include <folly/fibers/Promise-inl.h>