Reimplement std::future and std::promise to workaround TSAN false positives

include/dap/future.h

@@ -0,0 +1,179 @@
+// 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>& state) : state(state) {}
+
+template <typename T>
+bool future<T>::valid() const {
+  return 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