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// SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later
#include "core/hle/kernel/k_light_lock.h"
#include "core/hle/kernel/k_scheduler.h"
#include "core/hle/kernel/k_thread.h"
#include "core/hle/kernel/k_thread_queue.h"
#include "core/hle/kernel/kernel.h"
namespace Kernel {
namespace {
class ThreadQueueImplForKLightLock final : public KThreadQueue {
public:
explicit ThreadQueueImplForKLightLock(KernelCore& kernel_) : KThreadQueue(kernel_) {}
void CancelWait(KThread* waiting_thread, Result wait_result, bool cancel_timer_task) override {
// Remove the thread as a waiter from its owner.
if (KThread* owner = waiting_thread->GetLockOwner(); owner != nullptr) {
owner->RemoveWaiter(waiting_thread);
}
// Invoke the base cancel wait handler.
KThreadQueue::CancelWait(waiting_thread, wait_result, cancel_timer_task);
}
};
} // namespace
void KLightLock::Lock() {
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel));
while (true) {
uintptr_t old_tag = tag.load(std::memory_order_relaxed);
while (!tag.compare_exchange_weak(old_tag, (old_tag == 0) ? cur_thread : (old_tag | 1),
std::memory_order_acquire)) {
}
if (old_tag == 0 || this->LockSlowPath(old_tag | 1, cur_thread)) {
break;
}
}
}
void KLightLock::Unlock() {
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel));
uintptr_t expected = cur_thread;
if (!tag.compare_exchange_strong(expected, 0, std::memory_order_release)) {
this->UnlockSlowPath(cur_thread);
}
}
bool KLightLock::LockSlowPath(uintptr_t _owner, uintptr_t _cur_thread) {
KThread* cur_thread = reinterpret_cast<KThread*>(_cur_thread);
ThreadQueueImplForKLightLock wait_queue(kernel);
// Pend the current thread waiting on the owner thread.
{
KScopedSchedulerLock sl{kernel};
// Ensure we actually have locking to do.
if (tag.load(std::memory_order_relaxed) != _owner) {
return false;
}
// Add the current thread as a waiter on the owner.
KThread* owner_thread = reinterpret_cast<KThread*>(_owner & ~1ULL);
cur_thread->SetKernelAddressKey(reinterpret_cast<uintptr_t>(std::addressof(tag)));
owner_thread->AddWaiter(cur_thread);
// Begin waiting to hold the lock.
cur_thread->BeginWait(std::addressof(wait_queue));
if (owner_thread->IsSuspended()) {
owner_thread->ContinueIfHasKernelWaiters();
}
}
return true;
}
void KLightLock::UnlockSlowPath(uintptr_t _cur_thread) {
KThread* owner_thread = reinterpret_cast<KThread*>(_cur_thread);
// Unlock.
{
KScopedSchedulerLock sl(kernel);
// Get the next owner.
bool has_waiters;
KThread* next_owner = owner_thread->RemoveKernelWaiterByKey(
std::addressof(has_waiters), reinterpret_cast<uintptr_t>(std::addressof(tag)));
// Pass the lock to the next owner.
uintptr_t next_tag = 0;
if (next_owner != nullptr) {
next_tag =
reinterpret_cast<uintptr_t>(next_owner) | static_cast<uintptr_t>(has_waiters);
next_owner->EndWait(ResultSuccess);
if (next_owner->IsSuspended()) {
next_owner->ContinueIfHasKernelWaiters();
}
}
// We may have unsuspended in the process of acquiring the lock, so we'll re-suspend now if
// so.
if (owner_thread->IsSuspended()) {
owner_thread->TrySuspend();
}
// Write the new tag value.
tag.store(next_tag, std::memory_order_release);
}
}
bool KLightLock::IsLockedByCurrentThread() const {
return (tag | 1ULL) == (reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel)) | 1ULL);
}
} // namespace Kernel
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