Atmosphere/libraries/libmesosphere/include/mesosphere/kern_k_light_lock.hpp

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/*
* Copyright (c) 2018-2020 Atmosphère-NX
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
#include <mesosphere/kern_common.hpp>
#include <mesosphere/kern_select_cpu.hpp>
#include <mesosphere/kern_k_current_context.hpp>
#include <mesosphere/kern_k_scoped_lock.hpp>
namespace ams::kern {
class KLightLock {
private:
std::atomic<uintptr_t> m_tag;
public:
constexpr KLightLock() : m_tag(0) { /* ... */ }
void Lock() {
MESOSPHERE_ASSERT_THIS();
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer());
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const uintptr_t cur_thread_tag = (cur_thread | 1);
while (true) {
uintptr_t old_tag = m_tag.load(std::memory_order_relaxed);
while (!m_tag.compare_exchange_weak(old_tag, (old_tag == 0) ? cur_thread : old_tag | 1, std::memory_order_acquire)) {
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if ((old_tag | 1) == cur_thread_tag) {
return;
}
}
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if ((old_tag == 0) || ((old_tag | 1) == cur_thread_tag)) {
break;
}
this->LockSlowPath(old_tag | 1, cur_thread);
}
}
void Unlock() {
MESOSPHERE_ASSERT_THIS();
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer());
uintptr_t expected = cur_thread;
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do {
if (expected != cur_thread) {
return this->UnlockSlowPath(cur_thread);
}
} while (!m_tag.compare_exchange_weak(expected, 0, std::memory_order_release));
}
void LockSlowPath(uintptr_t owner, uintptr_t cur_thread);
void UnlockSlowPath(uintptr_t cur_thread);
bool IsLocked() const { return m_tag != 0; }
bool IsLockedByCurrentThread() const { return (m_tag | 0x1ul) == (reinterpret_cast<uintptr_t>(GetCurrentThreadPointer()) | 0x1ul); }
};
using KScopedLightLock = KScopedLock<KLightLock>;
}