116 lines
3.8 KiB
C++
116 lines
3.8 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <atomic>
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#include <condition_variable>
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namespace folly {
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/**
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* The behavior of the atomic_wait() family of functions is semantically
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* identical to futex(). Correspondingly, calling atomic_notify_one(),
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* atomic_notify_all() is identical to futexWake() with 1 and
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* std::numeric_limits<int>::max() respectively
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*
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* The difference here compared to the futex API above is that it works with
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* all types of atomic widths. When a 32 bit atomic integer is used, the
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* implementation falls back to using futex() if possible, and the
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* compatibility implementation for non-linux systems otherwise. For all
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* other integer widths, the compatibility implementation is used
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*
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* The templating of this API is changed from the standard in the following
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* ways
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*
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* - At the time of writing, libstdc++'s implementation of std::atomic<> does
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* not include the value_type alias. So we rely on the atomic type being a
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* template class such that the first type is the underlying value type
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* - The Atom parameter allows this API to be compatible with
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* DeterministicSchedule testing.
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* - atomic_wait_until() does not exist in the linked paper, the version here
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* is identical to futexWaitUntil() and returns std::cv_status
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*/
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// mimic: std::atomic_wait, p1135r0
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namespace detail {
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namespace atomic_notification {
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struct atomic_wait_fn {
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public:
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template <typename Atomic, typename Integer>
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constexpr void operator()(const Atomic* atomic, Integer integer) const {
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tag_invoke(*this, atomic, integer);
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}
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};
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} // namespace atomic_notification
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} // namespace detail
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constexpr inline auto atomic_wait =
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detail::atomic_notification::atomic_wait_fn{};
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// mimic: std::atomic_wait_until, p1135r0
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namespace detail {
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namespace atomic_notification {
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struct atomic_wait_until_fn {
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public:
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template <typename Atomic, typename Integer, typename Clock, typename Dur>
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constexpr std::cv_status operator()(
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const Atomic* atomic,
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Integer old,
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const std::chrono::time_point<Clock, Dur>& deadline) const {
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return tag_invoke(*this, atomic, old, deadline);
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}
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};
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} // namespace atomic_notification
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} // namespace detail
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constexpr inline auto atomic_wait_until =
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detail::atomic_notification::atomic_wait_until_fn{};
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// mimic: std::atomic_notify_one, p1135r0
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namespace detail {
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namespace atomic_notification {
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struct atomic_notify_one_fn {
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public:
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template <typename Atomic>
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constexpr void operator()(const Atomic* atomic) const {
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tag_invoke(*this, atomic);
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}
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};
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} // namespace atomic_notification
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} // namespace detail
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constexpr inline auto atomic_notify_one =
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detail::atomic_notification::atomic_notify_one_fn{};
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// mimic: std::atomic_notify_all, p1135r0
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namespace detail {
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namespace atomic_notification {
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struct atomic_notify_all_fn {
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public:
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template <typename Atomic>
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constexpr void operator()(Atomic* atomic) const {
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tag_invoke(*this, atomic);
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}
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};
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} // namespace atomic_notification
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} // namespace detail
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constexpr inline auto atomic_notify_all =
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detail::atomic_notification::atomic_notify_all_fn{};
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// mimic: std::atomic_uint_fast_wait_t, p1135r0
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using atomic_uint_fast_wait_t = std::atomic<std::uint32_t>;
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} // namespace folly
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#include <folly/synchronization/AtomicNotification-inl.h>
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