Seastar
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spinlock.hh
1/*
2 * This file is open source software, licensed to you under the terms
3 * of the Apache License, Version 2.0 (the "License"). See the NOTICE file
4 * distributed with this work for additional information regarding copyright
5 * ownership. You may not use this file except in compliance with the License.
6 *
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing,
12 * software distributed under the License is distributed on an
13 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14 * KIND, either express or implied. See the License for the
15 * specific language governing permissions and limitations
16 * under the License.
17 */
18/*
19 * Copyright 2016 ScyllaDB
20 */
21
22#pragma once
23
24#include <seastar/util/modules.hh>
25
26#ifndef SEASTAR_MODULE
27#include <atomic>
28#include <cassert>
29
30#if defined(__x86_64__) || defined(__i386__)
31#include <xmmintrin.h>
32#endif
33#endif
34
35namespace seastar {
36
37namespace internal {
38#if defined(__x86_64__) || defined(__i386__)
39
45[[gnu::always_inline]]
46inline void cpu_relax() {
47 _mm_pause();
48}
49
50#elif defined(__PPC__)
51
52[[gnu::always_inline]]
53inline void cpu_relax() {
54 __asm__ volatile("yield");
55}
56
57#elif defined(__s390x__) || defined(__zarch__)
58
59// FIXME: there must be a better way
60[[gnu::always_inline]]
61inline void cpu_relax() {}
62
63#elif defined(__aarch64__)
64
65[[gnu::always_inline]]
66inline void cpu_relax() {
67 __asm__ volatile("yield");
68}
69
70#else
71
72[[gnu::always_inline]]
73inline void cpu_relax() {}
74#warning "Using an empty cpu_relax() for this architecture"
75
76#endif
77
78
79}
80
81namespace util {
82
83// Spin lock implementation.
84// BasicLockable.
85// Async-signal safe.
86// unlock() "synchronizes with" lock().
87SEASTAR_MODULE_EXPORT
88class spinlock {
89 std::atomic<bool> _busy = { false };
90public:
91 spinlock() = default;
92 spinlock(const spinlock&) = delete;
93 ~spinlock() { assert(!_busy.load(std::memory_order_relaxed)); }
94 bool try_lock() noexcept {
95 return !_busy.exchange(true, std::memory_order_acquire);
96 }
97 void lock() noexcept {
98 while (_busy.exchange(true, std::memory_order_acquire)) {
99 while (_busy.load(std::memory_order_relaxed)) {
100 internal::cpu_relax();
101 }
102 }
103 }
104 void unlock() noexcept {
105 _busy.store(false, std::memory_order_release);
106 }
107};
108
109}
110
111}
Definition: spinlock.hh:88
Seastar API namespace.
Definition: abort_on_ebadf.hh:26