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

/*
 * 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_k_spin_lock.hpp>
#include <mesosphere/kern_k_current_context.hpp>
#include <mesosphere/kern_k_scoped_lock.hpp>

namespace ams::kern {

    class KThread;

    /*
        TODO: C++20

        template<typename T>
        concept KSchedulerLockable = !std::is_reference<T>::value && requires {
            { T::DisableScheduling()                    } -> std::same_as<void>;
            { T::EnableScheduling(std::declval<u64>())  } -> std::same_as<void>;
            { T::UpdateHighestPriorityThreads()         } -> std::convertible_to<u64>;
        };

    */

    template<typename SchedulerType> /* TODO C++20: requires KSchedulerLockable<SchedulerType> */
    class KAbstractSchedulerLock {
        private:
            KAlignedSpinLock spin_lock;
            s32 lock_count;
            KThread *owner_thread;
        public:
            constexpr ALWAYS_INLINE KAbstractSchedulerLock() : spin_lock(), lock_count(0), owner_thread(nullptr) { MESOSPHERE_ASSERT_THIS(); }

            ALWAYS_INLINE bool IsLockedByCurrentThread() const {
                MESOSPHERE_ASSERT_THIS();

                return this->owner_thread == GetCurrentThreadPointer();
            }

            ALWAYS_INLINE void Lock() {
                MESOSPHERE_ASSERT_THIS();

                if (this->IsLockedByCurrentThread()) {
                    /* If we already own the lock, we can just increment the count. */
                    MESOSPHERE_ASSERT(this->lock_count > 0);
                    this->lock_count++;
                } else {
                    /* Otherwise, we want to disable scheduling and acquire the spinlock. */
                    SchedulerType::DisableScheduling();
                    this->spin_lock.Lock();

                    /* For debug, ensure that our state is valid. */
                    MESOSPHERE_ASSERT(this->lock_count == 0);
                    MESOSPHERE_ASSERT(this->owner_thread == nullptr);

                    /* Increment count, take ownership. */
                    this->lock_count = 1;
                    this->owner_thread = GetCurrentThreadPointer();
                }
            }

            ALWAYS_INLINE void Unlock() {
                MESOSPHERE_ASSERT_THIS();
                MESOSPHERE_ASSERT(this->IsLockedByCurrentThread());
                MESOSPHERE_ASSERT(this->lock_count > 0);

                /* Release an instance of the lock. */
                if ((--this->lock_count) == 0) {
                    /* We're no longer going to hold the lock. Take note of what cores need scheduling. */
                    const u64 cores_needing_scheduling = SchedulerType::UpdateHighestPriorityThreads();

                   /* Note that we no longer hold the lock, and unlock the spinlock. */
                    this->owner_thread = nullptr;
                    this->spin_lock.Unlock();

                    /* Enable scheduling, and perform a rescheduling operation. */
                    SchedulerType::EnableScheduling(cores_needing_scheduling);
                }
            }
    };

}