text: /*
   * Copyright 2004-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 <atomic>
  #include <condition_variable>
  
  namespace folly {
  
  /**
   * The behavior of the atomic_wait() family of functions is semantically
   * identical to futex().  Correspondingly, calling atomic_notify_one(),
   * atomic_notify_all() is identical to futexWake() with 1 and
   * std::numeric_limits<int>::max() respectively
   *
   * The difference here compared to the futex API above is that it works with
   * all types of atomic widths.  When a 32 bit atomic integer is used, the
   * implementation falls back to using futex() if possible, and the
   * compatibility implementation for non-linux systems otherwise.  For all
   * other integer widths, the compatibility implementation is used
   *
   * The templating of this API is changed from the standard in the following
   * ways
   *
   * - At the time of writing, libstdc++'s implementation of std::atomic<> does
   *   not include the value_type alias.  So we rely on the atomic type being a
   *   template class such that the first type is the underlying value type
   * - The Atom parameter allows this API to be compatible with
   *   DeterministicSchedule testing.
   * - atomic_wait_until() does not exist in the linked paper, the version here
   *   is identical to futexWaitUntil() and returns std::cv_status
   */
  //  mimic: std::atomic_wait, p1135r0
  template <typename Integer>
  void atomic_wait(const std::atomic<Integer>* atomic, Integer expected);
  template <typename Integer, typename Clock, typename Duration>
  std::cv_status atomic_wait_until(
      const std::atomic<Integer>* atomic,
      Integer expected,
      const std::chrono::time_point<Clock, Duration>& deadline);
  
  //  mimic: std::atomic_notify_one, p1135r0
  template <typename Integer>
  void atomic_notify_one(const std::atomic<Integer>* atomic);
  //  mimic: std::atomic_notify_all, p1135r0
  template <typename Integer>
  void atomic_notify_all(const std::atomic<Integer>* atomic);
  
  //  mimic: std::atomic_uint_fast_wait_t, p1135r0
  using atomic_uint_fast_wait_t = std::atomic<std::uint32_t>;
  
  } // namespace folly
  
  #include <folly/synchronization/AtomicNotification-inl.h>
  