150 lines
5.0 KiB
C++
150 lines
5.0 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 <folly/detail/Futex.h>
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#include <folly/synchronization/ParkingLot.h>
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#include <condition_variable>
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#include <cstdint>
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namespace folly {
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namespace detail {
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namespace atomic_notification {
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/**
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* We use Futex<std::atomic> as the alias that has the lowest performance
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* overhead with respect to atomic notifications. Assert that
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* atomic_uint_fast_wait_t is the same as Futex<std::atomic>
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*/
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static_assert(std::is_same<atomic_uint_fast_wait_t, Futex<std::atomic>>{}, "");
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/**
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* Implementation and specializations for the atomic_wait() family of
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* functions
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*/
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inline std::cv_status toCvStatus(FutexResult result) {
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return (result == FutexResult::TIMEDOUT) ? std::cv_status::timeout
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: std::cv_status::no_timeout;
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}
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inline std::cv_status toCvStatus(ParkResult result) {
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return (result == ParkResult::Timeout) ? std::cv_status::timeout
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: std::cv_status::no_timeout;
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}
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// ParkingLot instantiation for futex management
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extern ParkingLot<std::uint32_t> parkingLot;
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template <template <typename...> class Atom, typename... Args>
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void atomic_wait_impl(
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const Atom<std::uint32_t, Args...>* atomic,
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std::uint32_t expected) {
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futexWait(atomic, expected);
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return;
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}
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template <template <typename...> class Atom, typename Integer, typename... Args>
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void atomic_wait_impl(const Atom<Integer, Args...>* atomic, Integer expected) {
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static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
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parkingLot.park(
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atomic, -1, [&] { return atomic->load() == expected; }, [] {});
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}
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template <
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template <typename...> class Atom,
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typename... Args,
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typename Clock,
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typename Duration>
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std::cv_status atomic_wait_until_impl(
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const Atom<std::uint32_t, Args...>* atomic,
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std::uint32_t expected,
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const std::chrono::time_point<Clock, Duration>& deadline) {
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return toCvStatus(futexWaitUntil(atomic, expected, deadline));
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}
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template <
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template <typename...> class Atom,
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typename Integer,
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typename... Args,
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typename Clock,
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typename Duration>
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std::cv_status atomic_wait_until_impl(
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const Atom<Integer, Args...>* atomic,
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Integer expected,
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const std::chrono::time_point<Clock, Duration>& deadline) {
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static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
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return toCvStatus(parkingLot.park_until(
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atomic, -1, [&] { return atomic->load() == expected; }, [] {}, deadline));
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}
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template <template <typename...> class Atom, typename... Args>
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void atomic_notify_one_impl(const Atom<std::uint32_t, Args...>* atomic) {
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futexWake(atomic, 1);
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return;
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}
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template <template <typename...> class Atom, typename Integer, typename... Args>
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void atomic_notify_one_impl(const Atom<Integer, Args...>* atomic) {
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static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
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parkingLot.unpark(atomic, [&](const auto& data) {
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FOLLY_SAFE_DCHECK(data == std::numeric_limits<std::uint32_t>::max(), "");
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return UnparkControl::RemoveBreak;
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});
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}
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template <template <typename...> class Atom, typename... Args>
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void atomic_notify_all_impl(const Atom<std::uint32_t, Args...>* atomic) {
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futexWake(atomic);
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return;
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}
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template <template <typename...> class Atom, typename Integer, typename... Args>
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void atomic_notify_all_impl(const Atom<Integer, Args...>* atomic) {
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static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
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parkingLot.unpark(atomic, [&](const auto& data) {
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FOLLY_SAFE_DCHECK(data == std::numeric_limits<std::uint32_t>::max(), "");
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return UnparkControl::RemoveContinue;
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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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template <typename Integer>
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void atomic_wait(const std::atomic<Integer>* atomic, Integer expected) {
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detail::atomic_notification::atomic_wait_impl(atomic, expected);
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}
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template <typename Integer, typename Clock, typename Duration>
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std::cv_status atomic_wait_until(
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const std::atomic<Integer>* atomic,
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Integer expected,
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const std::chrono::time_point<Clock, Duration>& deadline) {
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return detail::atomic_notification::atomic_wait_until_impl(
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atomic, expected, deadline);
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}
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template <typename Integer>
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void atomic_notify_one(const std::atomic<Integer>* atomic) {
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detail::atomic_notification::atomic_notify_one_impl(atomic);
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}
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template <typename Integer>
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void atomic_notify_all(const std::atomic<Integer>* atomic) {
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detail::atomic_notification::atomic_notify_all_impl(atomic);
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}
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} // namespace folly
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