/**************************************************************************/
/* spin_lock.h */
/**************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/**************************************************************************/
/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
/* */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the */
/* "Software"), to deal in the Software without restriction, including */
/* without limitation the rights to use, copy, modify, merge, publish, */
/* distribute, sublicense, and/or sell copies of the Software, and to */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions: */
/* */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/**************************************************************************/
#pragma once
#include "core/os/thread.h"
#include "core/typedefs.h"
#ifdef THREADS_ENABLED
// Note the implementations below avoid false sharing by ensuring their
// sizes match the assumed cache line. We can't use align attributes
// because these objects may end up unaligned in semi-tightly packed arrays.
#ifdef _MSC_VER
#include <intrin.h>
#endif
#if defined(__APPLE__)
#include <os/lock.h>
class SpinLock {
union {
mutable os_unfair_lock _lock = OS_UNFAIR_LOCK_INIT;
char aligner[Thread::CACHE_LINE_BYTES];
};
public:
_ALWAYS_INLINE_ void lock() const {
os_unfair_lock_lock(&_lock);
}
_ALWAYS_INLINE_ void unlock() const {
os_unfair_lock_unlock(&_lock);
}
};
#else // __APPLE__
#include <atomic>
_ALWAYS_INLINE_ static void _cpu_pause() {
#if defined(_MSC_VER)
// ----- MSVC.
#if defined(_M_ARM) || defined(_M_ARM64) // ARM.
__yield();
#elif defined(_M_IX86) || defined(_M_X64) // x86.
_mm_pause();
#endif
#elif defined(__GNUC__) || defined(__clang__)
// ----- GCC/Clang.
#if defined(__i386__) || defined(__x86_64__) // x86.
__builtin_ia32_pause();
#elif defined(__arm__) || defined(__aarch64__) // ARM.
asm volatile("yield");
#elif defined(__powerpc__) // PowerPC.
asm volatile("or 27,27,27");
#elif defined(__riscv) // RISC-V.
asm volatile(".insn i 0x0F, 0, x0, x0, 0x010");
#endif
#endif
}
static_assert(std::atomic_bool::is_always_lock_free);
class SpinLock {
union {
#if __cplusplus >= 202002L
mutable std::atomic<bool> locked = false;
#else
mutable std::atomic<bool> locked = ATOMIC_VAR_INIT(false);
#endif
char aligner[Thread::CACHE_LINE_BYTES];
};
public:
_ALWAYS_INLINE_ void lock() const {
while (true) {
bool expected = false;
if (locked.compare_exchange_weak(expected, true, std::memory_order_acquire, std::memory_order_relaxed)) {
break;
}
do {
_cpu_pause();
} while (locked.load(std::memory_order_relaxed));
}
}
_ALWAYS_INLINE_ void unlock() const {
locked.store(false, std::memory_order_release);
}
};
#endif // __APPLE__
#else // THREADS_ENABLED
class SpinLock {
public:
void lock() const {}
void unlock() const {}
};
#endif // THREADS_ENABLED