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// SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later
#include "core/hle/kernel/k_spin_lock.h"
#if defined(_M_X64) || defined(_M_IX86) || defined(__x86_64__) || defined(__i386__)
#include <immintrin.h>
#endif
namespace Kernel {
namespace {
// Spins of about 30-140 cycles each before a contended Lock sleeps (a few microseconds).
constexpr int SpinCount = 128;
void Pause() {
#if defined(_M_X64) || defined(_M_IX86) || defined(__x86_64__) || defined(__i386__)
_mm_pause();
#elif defined(__aarch64__)
asm volatile("yield");
#endif
}
} // Anonymous namespace
void KSpinLock::Lock() {
u32 expected = 0;
if (m_state.compare_exchange_strong(expected, 1, std::memory_order_acquire,
std::memory_order_relaxed)) {
return;
}
for (int spin = 0; spin < SpinCount; ++spin) {
Pause();
if (m_state.load(std::memory_order_relaxed) == 0) {
expected = 0;
if (m_state.compare_exchange_weak(expected, 1, std::memory_order_acquire,
std::memory_order_relaxed)) {
return;
}
}
}
// Mark the lock contended and sleep until it is released; taken this way it stays marked,
// so its Unlock wakes the next sleeper.
while (m_state.exchange(2, std::memory_order_acquire) != 0) {
m_state.wait(2, std::memory_order_relaxed);
}
}
void KSpinLock::Unlock() {
if (m_state.exchange(0, std::memory_order_release) == 2) {
m_state.notify_one();
}
}
bool KSpinLock::TryLock() {
u32 expected = 0;
return m_state.compare_exchange_strong(expected, 1, std::memory_order_acquire,
std::memory_order_relaxed);
}
} // namespace Kernel
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