Futex.h

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/*
 * Copyright 2013-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 <cassert>
#include <chrono>
#include <cstdint>
#include <limits>
#include <type_traits>

#include <folly/portability/Unistd.h>

namespace folly {
namespace detail {

enum class FutexResult {
  VALUE_CHANGED, /* futex value didn't match expected */
  AWOKEN, /* wakeup by matching futex wake, or spurious wakeup */
  INTERRUPTED, /* wakeup by interrupting signal */
  TIMEDOUT, /* wakeup by expiring deadline */
};

template <template <typename> class Atom = std::atomic>
using Futex = Atom<std::uint32_t>;

template <typename Futex>
FutexResult
futexWait(const Futex* futex, uint32_t expected, uint32_t waitMask = -1);

template <
    typename Futex,
    class Clock,
    class Duration = typename Clock::duration>
FutexResult futexWaitUntil(
    const Futex* futex,
    uint32_t expected,
    std::chrono::time_point<Clock, Duration> const& deadline,
    uint32_t waitMask = -1);

template <typename Futex>
int futexWake(
    const Futex* futex,
    int count = std::numeric_limits<int>::max(),
    uint32_t wakeMask = -1);

template <typename T>
struct EmulatedFutexAtomic : public std::atomic<T> {
  EmulatedFutexAtomic() noexcept = default;
  constexpr /* implicit */ EmulatedFutexAtomic(T init) noexcept
      : std::atomic<T>(init) {}
  // It doesn't copy or move
  EmulatedFutexAtomic(EmulatedFutexAtomic&& rhs) = delete;
};

} // namespace detail
} // namespace folly

#include <folly/detail/Futex-inl.h>