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111 lines
3.8 KiB
C++
111 lines
3.8 KiB
C++
/**************************************************************************/
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/* spin_lock.h */
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/**************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/**************************************************************************/
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/**************************************************************************/
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#ifndef SPIN_LOCK_H
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#define SPIN_LOCK_H
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#include "core/typedefs.h"
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#ifdef _MSC_VER
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#include <intrin.h>
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#endif
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#if defined(__APPLE__)
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#include <os/lock.h>
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class SpinLock {
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mutable os_unfair_lock _lock = OS_UNFAIR_LOCK_INIT;
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public:
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_ALWAYS_INLINE_ void lock() const {
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os_unfair_lock_lock(&_lock);
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}
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_ALWAYS_INLINE_ void unlock() const {
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os_unfair_lock_unlock(&_lock);
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}
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};
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#else
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#include "core/os/thread.h"
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#include <atomic>
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_ALWAYS_INLINE_ static void _cpu_pause() {
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#if defined(_MSC_VER)
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// ----- MSVC.
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#if defined(_M_ARM) || defined(_M_ARM64) // ARM.
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__yield();
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#elif defined(_M_IX86) || defined(_M_X64) // x86.
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_mm_pause();
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#endif
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#elif defined(__GNUC__) || defined(__clang__)
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// ----- GCC/Clang.
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#if defined(__i386__) || defined(__x86_64__) // x86.
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__builtin_ia32_pause();
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#elif defined(__arm__) || defined(__aarch64__) // ARM.
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asm volatile("yield");
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#elif defined(__powerpc__) || defined(__ppc__) || defined(__PPC__) // PowerPC.
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asm volatile("or 27,27,27");
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#elif defined(__riscv) // RISC-V.
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asm volatile(".insn i 0x0F, 0, x0, x0, 0x010");
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#endif
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#endif
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}
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static_assert(std::atomic_bool::is_always_lock_free);
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class alignas(Thread::CACHE_LINE_BYTES) SpinLock {
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mutable std::atomic<bool> locked = ATOMIC_VAR_INIT(false);
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public:
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_ALWAYS_INLINE_ void lock() const {
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while (true) {
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bool expected = false;
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if (locked.compare_exchange_weak(expected, true, std::memory_order_acquire, std::memory_order_relaxed)) {
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break;
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}
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do {
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_cpu_pause();
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} while (locked.load(std::memory_order_relaxed));
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}
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}
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_ALWAYS_INLINE_ void unlock() const {
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locked.store(false, std::memory_order_release);
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}
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};
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#endif // __APPLE__
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#endif // SPIN_LOCK_H
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