| // Copyright 2019 Google LLC |
| // |
| // 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 |
| // |
| // https://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 dap_future_h |
| #define dap_future_h |
| |
| #include <condition_variable> |
| #include <memory> |
| #include <mutex> |
| |
| namespace dap { |
| |
| // internal functionality |
| namespace detail { |
| template <typename T> |
| struct promise_state { |
| T val; |
| std::mutex mutex; |
| std::condition_variable cv; |
| bool hasVal = false; |
| }; |
| } // namespace detail |
| |
| // forward declaration |
| template <typename T> |
| class promise; |
| |
| // future_status is the enumeration returned by future::wait_for and |
| // future::wait_until. |
| enum class future_status { |
| ready, |
| timeout, |
| }; |
| |
| // future is a minimal reimplementation of std::future, that does not suffer |
| // from TSAN false positives. See: |
| // https://gcc.gnu.org/bugzilla//show_bug.cgi?id=69204 |
| template <typename T> |
| class future { |
| public: |
| using State = detail::promise_state<T>; |
| |
| // constructors |
| inline future() = default; |
| inline future(future&&) = default; |
| |
| // valid() returns true if the future has an internal state. |
| bool valid() const; |
| |
| // get() blocks until the future has a valid result, and returns it. |
| // The future must have a valid internal state to call this method. |
| inline T get(); |
| |
| // wait() blocks until the future has a valid result. |
| // The future must have a valid internal state to call this method. |
| void wait() const; |
| |
| // wait_for() blocks until the future has a valid result, or the timeout is |
| // reached. |
| // The future must have a valid internal state to call this method. |
| template <class Rep, class Period> |
| future_status wait_for( |
| const std::chrono::duration<Rep, Period>& timeout) const; |
| |
| // wait_until() blocks until the future has a valid result, or the timeout is |
| // reached. |
| // The future must have a valid internal state to call this method. |
| template <class Clock, class Duration> |
| future_status wait_until( |
| const std::chrono::time_point<Clock, Duration>& timeout) const; |
| |
| private: |
| friend promise<T>; |
| future(const future&) = delete; |
| inline future(const std::shared_ptr<State>& state); |
| |
| std::shared_ptr<State> state = std::make_shared<State>(); |
| }; |
| |
| template <typename T> |
| future<T>::future(const std::shared_ptr<State>& s) : state(s) {} |
| |
| template <typename T> |
| bool future<T>::valid() const { |
| return static_cast<bool>(state); |
| } |
| |
| template <typename T> |
| T future<T>::get() { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| state->cv.wait(lock, [&] { return state->hasVal; }); |
| return state->val; |
| } |
| |
| template <typename T> |
| void future<T>::wait() const { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| state->cv.wait(lock, [&] { return state->hasVal; }); |
| } |
| |
| template <typename T> |
| template <class Rep, class Period> |
| future_status future<T>::wait_for( |
| const std::chrono::duration<Rep, Period>& timeout) const { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| return state->cv.wait_for(lock, timeout, [&] { return state->hasVal; }) |
| ? future_status::ready |
| : future_status::timeout; |
| } |
| |
| template <typename T> |
| template <class Clock, class Duration> |
| future_status future<T>::wait_until( |
| const std::chrono::time_point<Clock, Duration>& timeout) const { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| return state->cv.wait_until(lock, timeout, [&] { return state->hasVal; }) |
| ? future_status::ready |
| : future_status::timeout; |
| } |
| |
| // promise is a minimal reimplementation of std::promise, that does not suffer |
| // from TSAN false positives. See: |
| // https://gcc.gnu.org/bugzilla//show_bug.cgi?id=69204 |
| template <typename T> |
| class promise { |
| public: |
| // constructors |
| inline promise() = default; |
| inline promise(promise&& other) = default; |
| inline promise(const promise& other) = default; |
| |
| // set_value() stores value to the shared state. |
| // set_value() must only be called once. |
| inline void set_value(const T& value) const; |
| inline void set_value(T&& value) const; |
| |
| // get_future() returns a future sharing this promise's state. |
| future<T> get_future(); |
| |
| private: |
| using State = detail::promise_state<T>; |
| std::shared_ptr<State> state = std::make_shared<State>(); |
| }; |
| |
| template <typename T> |
| future<T> promise<T>::get_future() { |
| return future<T>(state); |
| } |
| |
| template <typename T> |
| void promise<T>::set_value(const T& value) const { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| state->val = value; |
| state->hasVal = true; |
| state->cv.notify_all(); |
| } |
| |
| template <typename T> |
| void promise<T>::set_value(T&& value) const { |
| std::unique_lock<std::mutex> lock(state->mutex); |
| state->val = std::move(value); |
| state->hasVal = true; |
| state->cv.notify_all(); |
| } |
| |
| } // namespace dap |
| |
| #endif // dap_future_h |