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Atmosphere/libraries/libmesosphere/source/kern_k_light_lock.cpp

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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/>.
*/
#include <mesosphere.hpp>
namespace ams::kern {
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;
/* Ensure we actually have locking to do. */
if (AMS_UNLIKELY(m_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(m_tag)));
owner_thread->AddWaiter(cur_thread);
/* Set thread states. */
cur_thread->SetState(KThread::ThreadState_Waiting);
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if (owner_thread->IsSuspended()) {
owner_thread->ContinueIfHasKernelWaiters();
}
}
/* We're no longer waiting on the lock owner. */
{
KScopedSchedulerLock sl;
if (KThread *owner_thread = cur_thread->GetLockOwner(); AMS_UNLIKELY(owner_thread != nullptr)) {
owner_thread->RemoveWaiter(cur_thread);
}
}
}
void KLightLock::UnlockSlowPath(uintptr_t _cur_thread) {
KThread *owner_thread = reinterpret_cast<KThread *>(_cur_thread);
/* Unlock. */
{
KScopedSchedulerLock sl;
/* Get the next owner. */
s32 num_waiters = 0;
KThread *next_owner = owner_thread->RemoveWaiterByKey(std::addressof(num_waiters), reinterpret_cast<uintptr_t>(std::addressof(m_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);
if (num_waiters > 1) {
next_tag |= 0x1;
}
next_owner->SetState(KThread::ThreadState_Runnable);
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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. */
m_tag.store(next_tag);
}
}
}