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// Copyright 2021 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#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/kernel.h"
namespace Kernel {
void KLightLock::Lock() {
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel));
const uintptr_t cur_thread_tag = (cur_thread | 1);
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 | 1) == cur_thread_tag) {
return;
}
}
if ((old_tag == 0) || ((old_tag | 1) == cur_thread_tag)) {
break;
}
LockSlowPath(old_tag | 1, cur_thread);
}
}
void KLightLock::Unlock() {
const uintptr_t cur_thread = reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel));
uintptr_t expected = cur_thread;
do {
if (expected != cur_thread) {
return UnlockSlowPath(cur_thread);
}
} while (!tag.compare_exchange_weak(expected, 0, std::memory_order_release));
}
void KLightLock::LockSlowPath(uintptr_t _owner, uintptr_t _cur_thread) {
KThread* cur_thread = reinterpret_cast<KThread*>(_cur_thread);
// 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;
}
// Add the current thread as a waiter on the owner.
KThread* owner_thread = reinterpret_cast<KThread*>(_owner & ~1ul);
cur_thread->SetAddressKey(reinterpret_cast<uintptr_t>(std::addressof(tag)));
owner_thread->AddWaiter(cur_thread);
// Set thread states.
if (cur_thread->GetState() == ThreadState::Runnable) {
cur_thread->SetState(ThreadState::Waiting);
} else {
KScheduler::SetSchedulerUpdateNeeded(kernel);
}
if (owner_thread->IsSuspended()) {
owner_thread->ContinueIfHasKernelWaiters();
KScheduler::SetSchedulerUpdateNeeded(kernel);
}
}
// We're no longer waiting on the lock owner.
{
KScopedSchedulerLock sl{kernel};
KThread* owner_thread = cur_thread->GetLockOwner();
if (owner_thread) {
owner_thread->RemoveWaiter(cur_thread);
}
}
}
void KLightLock::UnlockSlowPath(uintptr_t _cur_thread) {
KThread* owner_thread = reinterpret_cast<KThread*>(_cur_thread);
// Unlock.
{
KScopedSchedulerLock sl{kernel};
// Get the next owner.
s32 num_waiters = 0;
KThread* next_owner = owner_thread->RemoveWaiterByKey(
std::addressof(num_waiters), reinterpret_cast<uintptr_t>(std::addressof(tag)));
// Pass the lock to the next owner.
uintptr_t next_tag = 0;
if (next_owner) {
next_tag = reinterpret_cast<uintptr_t>(next_owner);
if (num_waiters > 1) {
next_tag |= 0x1;
}
if (next_owner->GetState() == ThreadState::Waiting) {
next_owner->SetState(ThreadState::Runnable);
} else {
KScheduler::SetSchedulerUpdateNeeded(kernel);
}
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);
}
}
bool KLightLock::IsLockedByCurrentThread() const {
return (tag | 0x1ul) == (reinterpret_cast<uintptr_t>(GetCurrentThreadPointer(kernel)) | 0x1ul);
}
} // namespace Kernel
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