1/*
2 * Copyright 2004-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16#pragma once
17
18#include <folly/detail/Futex.h>
19#include <folly/synchronization/ParkingLot.h>
20
21#include <condition_variable>
22#include <cstdint>
23
24namespace folly {
25namespace detail {
26namespace atomic_notification {
27/**
28 * We use Futex<std::atomic> as the alias that has the lowest performance
29 * overhead with respect to atomic notifications. Assert that
30 * atomic_uint_fast_wait_t is the same as Futex<std::atomic>
31 */
32static_assert(std::is_same<atomic_uint_fast_wait_t, Futex<std::atomic>>{}, "");
33
34/**
35 * Implementation and specializations for the atomic_wait() family of
36 * functions
37 */
38inline std::cv_status toCvStatus(FutexResult result) {
39 return (result == FutexResult::TIMEDOUT) ? std::cv_status::timeout
40 : std::cv_status::no_timeout;
41}
42inline std::cv_status toCvStatus(ParkResult result) {
43 return (result == ParkResult::Timeout) ? std::cv_status::timeout
44 : std::cv_status::no_timeout;
45}
46
47// ParkingLot instantiation for futex management
48extern ParkingLot<std::uint32_t> parkingLot;
49
50template <template <typename...> class Atom, typename... Args>
51void atomic_wait_impl(
52 const Atom<std::uint32_t, Args...>* atomic,
53 std::uint32_t expected) {
54 futexWait(atomic, expected);
55 return;
56}
57
58template <template <typename...> class Atom, typename Integer, typename... Args>
59void atomic_wait_impl(const Atom<Integer, Args...>* atomic, Integer expected) {
60 static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
61 parkingLot.park(
62 atomic, -1, [&] { return atomic->load() == expected; }, [] {});
63}
64
65template <
66 template <typename...> class Atom,
67 typename... Args,
68 typename Clock,
69 typename Duration>
70std::cv_status atomic_wait_until_impl(
71 const Atom<std::uint32_t, Args...>* atomic,
72 std::uint32_t expected,
73 const std::chrono::time_point<Clock, Duration>& deadline) {
74 return toCvStatus(futexWaitUntil(atomic, expected, deadline));
75}
76
77template <
78 template <typename...> class Atom,
79 typename Integer,
80 typename... Args,
81 typename Clock,
82 typename Duration>
83std::cv_status atomic_wait_until_impl(
84 const Atom<Integer, Args...>* atomic,
85 Integer expected,
86 const std::chrono::time_point<Clock, Duration>& deadline) {
87 static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
88 return toCvStatus(parkingLot.park_until(
89 atomic, -1, [&] { return atomic->load() == expected; }, [] {}, deadline));
90}
91
92template <template <typename...> class Atom, typename... Args>
93void atomic_notify_one_impl(const Atom<std::uint32_t, Args...>* atomic) {
94 futexWake(atomic, 1);
95 return;
96}
97
98template <template <typename...> class Atom, typename Integer, typename... Args>
99void atomic_notify_one_impl(const Atom<Integer, Args...>* atomic) {
100 static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
101 parkingLot.unpark(atomic, [&](const auto& data) {
102 FOLLY_SAFE_DCHECK(data == std::numeric_limits<std::uint32_t>::max(), "");
103 return UnparkControl::RemoveBreak;
104 });
105}
106
107template <template <typename...> class Atom, typename Integer, typename... Args>
108void atomic_notify_all_impl(const Atom<std::uint32_t, Args...>* atomic) {
109 futexWake(atomic);
110 return;
111}
112
113template <template <typename...> class Atom, typename Integer, typename... Args>
114void atomic_notify_all_impl(const Atom<Integer, Args...>* atomic) {
115 static_assert(!std::is_same<Integer, std::uint32_t>{}, "");
116 parkingLot.unpark(atomic, [&](const auto& data) {
117 FOLLY_SAFE_DCHECK(data == std::numeric_limits<std::uint32_t>::max(), "");
118 return UnparkControl::RemoveContinue;
119 });
120}
121} // namespace atomic_notification
122} // namespace detail
123
124template <typename Integer>
125void atomic_wait(const std::atomic<Integer>* atomic, Integer expected) {
126 detail::atomic_notification::atomic_wait_impl(atomic, expected);
127}
128
129template <typename Integer, typename Clock, typename Duration>
130std::cv_status atomic_wait_until(
131 const std::atomic<Integer>* atomic,
132 Integer expected,
133 const std::chrono::time_point<Clock, Duration>& deadline) {
134 return detail::atomic_notification::atomic_wait_until_impl(
135 atomic, expected, deadline);
136}
137
138template <typename Integer>
139void atomic_notify_one(const std::atomic<Integer>* atomic) {
140 detail::atomic_notification::atomic_notify_one_impl(atomic);
141}
142
143template <typename Integer>
144void atomic_notify_all(const std::atomic<Integer>* atomic) {
145 detail::atomic_notification::atomic_notify_all_impl(atomic);
146}
147
148} // namespace folly
149