promise.h

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef FLUTTER_IMPELLER_BASE_PROMISE_H_
#define FLUTTER_IMPELLER_BASE_PROMISE_H_
 
#include <future>
 
namespace impeller {
 
template <class T>
std::future<T> RealizedFuture(T t) {
  std::promise<T> promise;
  auto future = promise.get_future();
  promise.set_value(std::move(t));
  return future;
}
 
// Wraps a std::promise and completes the promise with a value during
// destruction if the promise does not already have a value.
//
// By default the std::promise destructor will complete an empty promise with an
// exception. This will fail because Flutter is built without exception support.
template <typename T>
class NoExceptionPromise {
 public:
  NoExceptionPromise() = default;
 
  ~NoExceptionPromise() {
    if (!value_set_) {
      promise_.set_value({});
    }
  }
 
  std::future<T> get_future() { return promise_.get_future(); }
 
  void set_value(const T& value) {
    promise_.set_value(value);
    value_set_ = true;
  }
 
 private:
  std::promise<T> promise_;
  bool value_set_ = false;
};
 
}  // namespace impeller
 
#endif  // FLUTTER_IMPELLER_BASE_PROMISE_H_