ladybird/Kernel/Scheduler.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/QuickSort.h>
#include <AK/ScopeGuard.h>
#include <AK/TemporaryChange.h>
#include <AK/Time.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/Net/Socket.h>
#include <Kernel/Process.h>
#include <Kernel/Profiling.h>
#include <Kernel/RTC.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Time/TimeManagement.h>
#include <Kernel/TimerQueue.h>

//#define LOG_EVERY_CONTEXT_SWITCH
//#define SCHEDULER_DEBUG
//#define SCHEDULER_RUNNABLE_DEBUG

namespace Kernel {

class SchedulerPerProcessorData {
    AK_MAKE_NONCOPYABLE(SchedulerPerProcessorData);
    AK_MAKE_NONMOVABLE(SchedulerPerProcessorData);

public:
    SchedulerPerProcessorData() = default;

    WeakPtr<Thread> m_pending_beneficiary;
    const char* m_pending_donate_reason { nullptr };
    bool m_in_scheduler { true };
};

SchedulerData* g_scheduler_data;
timeval g_timeofday;
RecursiveSpinLock g_scheduler_lock;

void Scheduler::init_thread(Thread& thread)
{
    ASSERT(g_scheduler_data);
    g_scheduler_data->m_nonrunnable_threads.append(thread);
}

static u32 time_slice_for(const Thread& thread)
{
    // One time slice unit == 1ms
    if (&thread == Processor::current().idle_thread())
        return 1;
    return 10;
}

timeval Scheduler::time_since_boot()
{
    return { TimeManagement::the().seconds_since_boot(), (suseconds_t)TimeManagement::the().ticks_this_second() * 1000 };
}

Thread* g_finalizer;
WaitQueue* g_finalizer_wait_queue;
Atomic<bool> g_finalizer_has_work { false };
static Process* s_colonel_process;
u64 g_uptime;

Thread::JoinBlocker::JoinBlocker(Thread& joinee, KResult& try_join_result, void*& joinee_exit_value)
    : m_joinee(&joinee)
    , m_joinee_exit_value(joinee_exit_value)
{
    auto* current_thread = Thread::current();
    // We need to hold our lock to avoid a race where try_join succeeds
    // but the joinee is joining immediately
    ScopedSpinLock lock(m_lock);
    try_join_result = joinee.try_join(*current_thread);
    m_join_error = try_join_result.is_error();
}

void Thread::JoinBlocker::was_unblocked()
{
    ScopedSpinLock lock(m_lock);
    if (!m_join_error && m_joinee) {
        // If the joinee hasn't exited yet, remove ourselves now
        ASSERT(m_joinee != Thread::current());
        m_joinee->join_done();
        m_joinee = nullptr;
    }
}

bool Thread::JoinBlocker::should_unblock(Thread&)
{
    // We need to acquire our lock as the joinee could call joinee_exited
    // at any moment
    ScopedSpinLock lock(m_lock);

    if (m_join_error) {
        // Thread::block calls should_unblock before actually blocking.
        // If detected that we can't really block due to an error, we'll
        // return true here, which will cause Thread::block to return
        // with BlockResult::NotBlocked. Technically, because m_join_error
        // will only be set in the constructor, we don't need any lock
        // to check for it, but at the same time there should not be
        // any contention, either...
        return true;
    }

    return m_joinee == nullptr;
}

void Thread::JoinBlocker::joinee_exited(void* value)
{
    ScopedSpinLock lock(m_lock);
    if (!m_joinee) {
        // m_joinee can be nullptr if the joiner timed out and the
        // joinee waits on m_lock while the joiner holds it but has
        // not yet called join_done.
        return;
    }

    m_joinee_exit_value = value;
    m_joinee = nullptr;
    set_interrupted_by_death();
}

Thread::FileDescriptionBlocker::FileDescriptionBlocker(const FileDescription& description)
    : m_blocked_description(description)
{
}

const FileDescription& Thread::FileDescriptionBlocker::blocked_description() const
{
    return m_blocked_description;
}

Thread::AcceptBlocker::AcceptBlocker(const FileDescription& description)
    : FileDescriptionBlocker(description)
{
}

bool Thread::AcceptBlocker::should_unblock(Thread&)
{
    auto& socket = *blocked_description().socket();
    return socket.can_accept();
}

Thread::ConnectBlocker::ConnectBlocker(const FileDescription& description)
    : FileDescriptionBlocker(description)
{
}

bool Thread::ConnectBlocker::should_unblock(Thread&)
{
    auto& socket = *blocked_description().socket();
    return socket.setup_state() == Socket::SetupState::Completed;
}

Thread::WriteBlocker::WriteBlocker(const FileDescription& description)
    : FileDescriptionBlocker(description)
{
}

timespec* Thread::WriteBlocker::override_timeout(timespec* timeout)
{
    auto& description = blocked_description();
    if (description.is_socket()) {
        auto& socket = *description.socket();
        if (socket.has_send_timeout()) {
            timeval_to_timespec(Scheduler::time_since_boot(), m_deadline);
            timespec_add_timeval(m_deadline, socket.send_timeout(), m_deadline);
            if (!timeout || m_deadline < *timeout)
                return &m_deadline;
        }
    }
    return timeout;
}

bool Thread::WriteBlocker::should_unblock(Thread&)
{
    return blocked_description().can_write();
}

Thread::ReadBlocker::ReadBlocker(const FileDescription& description)
    : FileDescriptionBlocker(description)
{
}

timespec* Thread::ReadBlocker::override_timeout(timespec* timeout)
{
    auto& description = blocked_description();
    if (description.is_socket()) {
        auto& socket = *description.socket();
        if (socket.has_receive_timeout()) {
            timeval_to_timespec(Scheduler::time_since_boot(), m_deadline);
            timespec_add_timeval(m_deadline, socket.receive_timeout(), m_deadline);
            if (!timeout || m_deadline < *timeout)
                return &m_deadline;
        }
    }
    return timeout;
}

bool Thread::ReadBlocker::should_unblock(Thread&)
{
    return blocked_description().can_read();
}

Thread::ConditionBlocker::ConditionBlocker(const char* state_string, Function<bool()>&& condition)
    : m_block_until_condition(move(condition))
    , m_state_string(state_string)
{
    ASSERT(m_block_until_condition);
}

bool Thread::ConditionBlocker::should_unblock(Thread&)
{
    return m_block_until_condition();
}

Thread::SleepBlocker::SleepBlocker(u64 wakeup_time)
    : m_wakeup_time(wakeup_time)
{
}

bool Thread::SleepBlocker::should_unblock(Thread&)
{
    return m_wakeup_time <= g_uptime;
}

Thread::SelectBlocker::SelectBlocker(const FDVector& read_fds, const FDVector& write_fds, const FDVector& except_fds)
    : m_select_read_fds(read_fds)
    , m_select_write_fds(write_fds)
    , m_select_exceptional_fds(except_fds)
{
}

bool Thread::SelectBlocker::should_unblock(Thread& thread)
{
    auto& process = thread.process();
    for (int fd : m_select_read_fds) {
        if (!process.m_fds[fd])
            continue;
        if (process.m_fds[fd].description()->can_read())
            return true;
    }
    for (int fd : m_select_write_fds) {
        if (!process.m_fds[fd])
            continue;
        if (process.m_fds[fd].description()->can_write())
            return true;
    }

    return false;
}

Thread::WaitBlocker::WaitBlocker(int wait_options, ProcessID& waitee_pid)
    : m_wait_options(wait_options)
    , m_waitee_pid(waitee_pid)
{
}

bool Thread::WaitBlocker::should_unblock(Thread& thread)
{
    bool should_unblock = m_wait_options & WNOHANG;
    if (m_waitee_pid != -1) {
        auto peer = Process::from_pid(m_waitee_pid);
        if (!peer)
            return true;
    }
    thread.process().for_each_child([&](Process& child) {
        if (m_waitee_pid != -1 && m_waitee_pid != child.pid())
            return IterationDecision::Continue;

        bool child_exited = child.is_dead();
        bool child_stopped = false;
        if (child.thread_count()) {
            child.for_each_thread([&](auto& child_thread) {
                if (child_thread.state() == Thread::State::Stopped && !child_thread.has_pending_signal(SIGCONT)) {
                    child_stopped = true;
                    return IterationDecision::Break;
                }
                return IterationDecision::Continue;
            });
        }

        bool fits_the_spec = ((m_wait_options & WEXITED) && child_exited)
            || ((m_wait_options & WSTOPPED) && child_stopped);

        if (!fits_the_spec)
            return IterationDecision::Continue;

        m_waitee_pid = child.pid();
        should_unblock = true;
        return IterationDecision::Break;
    });
    return should_unblock;
}

Thread::SemiPermanentBlocker::SemiPermanentBlocker(Reason reason)
    : m_reason(reason)
{
}

bool Thread::SemiPermanentBlocker::should_unblock(Thread&)
{
    // someone else has to unblock us
    return false;
}

// Called by the scheduler on threads that are blocked for some reason.
// Make a decision as to whether to unblock them or not.
void Thread::consider_unblock(time_t now_sec, long now_usec)
{
    ScopedSpinLock lock(m_lock);
    switch (state()) {
    case Thread::Invalid:
    case Thread::Runnable:
    case Thread::Running:
    case Thread::Dead:
    case Thread::Stopped:
    case Thread::Queued:
    case Thread::Dying:
        /* don't know, don't care */
        return;
    case Thread::Blocked: {
        ASSERT(m_blocker != nullptr);
        timespec now;
        now.tv_sec = now_sec,
        now.tv_nsec = now_usec * 1000ull;
        bool timed_out = m_blocker_timeout && now >= *m_blocker_timeout;
        if (timed_out || m_blocker->should_unblock(*this))
            unblock();
        return;
    }
    }
}

void Scheduler::start()
{
    ASSERT_INTERRUPTS_DISABLED();

    // We need to acquire our scheduler lock, which will be released
    // by the idle thread once control transferred there
    g_scheduler_lock.lock();

    auto& processor = Processor::current();
    processor.set_scheduler_data(*new SchedulerPerProcessorData());
    ASSERT(processor.is_initialized());
    auto& idle_thread = *processor.idle_thread();
    ASSERT(processor.current_thread() == &idle_thread);
    ASSERT(processor.idle_thread() == &idle_thread);
    idle_thread.set_ticks_left(time_slice_for(idle_thread));
    idle_thread.did_schedule();
    idle_thread.set_initialized(true);
    processor.init_context(idle_thread, false);
    idle_thread.set_state(Thread::Running);
    ASSERT(idle_thread.affinity() == (1u << processor.id()));
    processor.initialize_context_switching(idle_thread);
    ASSERT_NOT_REACHED();
}

bool Scheduler::pick_next()
{
    ASSERT_INTERRUPTS_DISABLED();

    auto current_thread = Thread::current();
    auto now = time_since_boot();

    auto now_sec = now.tv_sec;
    auto now_usec = now.tv_usec;

    // Set the m_in_scheduler flag before acquiring the spinlock. This
    // prevents a recursive call into Scheduler::invoke_async upon
    // leaving the scheduler lock.
    ScopedCritical critical;
    auto& scheduler_data = Processor::current().get_scheduler_data();
    scheduler_data.m_in_scheduler = true;
    ScopeGuard guard(
        []() {
            // We may be on a different processor after we got switched
            // back to this thread!
            auto& scheduler_data = Processor::current().get_scheduler_data();
            ASSERT(scheduler_data.m_in_scheduler);
            scheduler_data.m_in_scheduler = false;
        });

    ScopedSpinLock lock(g_scheduler_lock);

    if (current_thread->should_die() && current_thread->state() == Thread::Running) {
        // Rather than immediately killing threads, yanking the kernel stack
        // away from them (which can lead to e.g. reference leaks), we always
        // allow Thread::wait_on to return. This allows the kernel stack to
        // clean up and eventually we'll get here shortly before transitioning
        // back to user mode (from Processor::exit_trap). At this point we
        // no longer want to schedule this thread. We can't wait until
        // Scheduler::enter_current because we don't want to allow it to
        // transition back to user mode.
#ifdef SCHEDULER_DEBUG
        dbg() << "Scheduler[" << Processor::current().id() << "]: Thread " << *current_thread << " is dying";
#endif
        current_thread->set_state(Thread::Dying);
    }

    // Check and unblock threads whose wait conditions have been met.
    Scheduler::for_each_nonrunnable([&](Thread& thread) {
        thread.consider_unblock(now_sec, now_usec);
        return IterationDecision::Continue;
    });

    Process::for_each([&](Process& process) {
        if (process.is_dead()) {
            if (current_thread->process().pid() != process.pid() && (!process.ppid() || !Process::from_pid(process.ppid()))) {
                auto name = process.name();
                auto pid = process.pid();
                auto exit_status = Process::reap(process);
                dbg() << "Scheduler[" << Processor::current().id() << "]: Reaped unparented process " << name << "(" << pid.value() << "), exit status: " << exit_status.si_status;
            }
            return IterationDecision::Continue;
        }
        if (process.m_alarm_deadline && g_uptime > process.m_alarm_deadline) {
            process.m_alarm_deadline = 0;
            // FIXME: Should we observe this signal somehow?
            (void)process.send_signal(SIGALRM, nullptr);
        }
        return IterationDecision::Continue;
    });

    // Dispatch any pending signals.
    Thread::for_each_living([&](Thread& thread) -> IterationDecision {
        ScopedSpinLock lock(thread.get_lock());
        if (!thread.has_unmasked_pending_signals())
            return IterationDecision::Continue;
        // NOTE: dispatch_one_pending_signal() may unblock the process.
        bool was_blocked = thread.is_blocked();
        if (thread.dispatch_one_pending_signal() == ShouldUnblockThread::No)
            return IterationDecision::Continue;
        if (was_blocked) {
#ifdef SCHEDULER_DEBUG
            dbg() << "Scheduler[" << Processor::current().id() << "]:Unblock " << thread << " due to signal";
#endif
            ASSERT(thread.m_blocker != nullptr);
            thread.m_blocker->set_interrupted_by_signal();
            thread.unblock();
        }
        return IterationDecision::Continue;
    });

#ifdef SCHEDULER_RUNNABLE_DEBUG
    dbg() << "Scheduler[" << Processor::current().id() << "]: Non-runnables:";
    Scheduler::for_each_nonrunnable([&](Thread& thread) -> IterationDecision {
        if (thread.state() == Thread::Queued)
            dbg() << "  " << String::format("%-12s", thread.state_string()) << " " << thread << " @ " << String::format("%w", thread.tss().cs) << ":" << String::format("%x", thread.tss().eip) << " Reason: " << (thread.wait_reason() ? thread.wait_reason() : "none");
        else if (thread.state() == Thread::Dying)
            dbg() << "  " << String::format("%-12s", thread.state_string()) << " " << thread << " @ " << String::format("%w", thread.tss().cs) << ":" << String::format("%x", thread.tss().eip) << " Finalizable: " << thread.is_finalizable();
        else
            dbg() << "  " << String::format("%-12s", thread.state_string()) << " " << thread << " @ " << String::format("%w", thread.tss().cs) << ":" << String::format("%x", thread.tss().eip);
        return IterationDecision::Continue;
    });

    dbg() << "Scheduler[" << Processor::current().id() << "]: Runnables:";
    Scheduler::for_each_runnable([](Thread& thread) -> IterationDecision {
        dbg() << "  " << String::format("%3u", thread.effective_priority()) << "/" << String::format("%2u", thread.priority()) << " " << String::format("%-12s", thread.state_string()) << " " << thread << " @ " << String::format("%w", thread.tss().cs) << ":" << String::format("%x", thread.tss().eip);
        return IterationDecision::Continue;
    });
#endif

    Thread* thread_to_schedule = nullptr;

    Vector<Thread*, 128> sorted_runnables;
    for_each_runnable([&](auto& thread) {
        if ((thread.affinity() & (1u << Processor::current().id())) == 0)
            return IterationDecision::Continue;
        if (thread.state() == Thread::Running && &thread != current_thread)
            return IterationDecision::Continue;
        sorted_runnables.append(&thread);
        if (&thread == scheduler_data.m_pending_beneficiary) {
            thread_to_schedule = &thread;
            return IterationDecision::Break;
        }
        return IterationDecision::Continue;
    });

    if (thread_to_schedule) {
        // The thread we're supposed to donate to still exists
        const char* reason = scheduler_data.m_pending_donate_reason;
        scheduler_data.m_pending_beneficiary = nullptr;
        scheduler_data.m_pending_donate_reason = nullptr;

        // We need to leave our first critical section before switching context,
        // but since we're still holding the scheduler lock we're still in a critical section
        critical.leave();

#ifdef SCHEDULER_DEBUG
        dbg() << "Processing pending donate to " << *thread_to_schedule << " reason=" << reason;
#endif
        return donate_to_and_switch(thread_to_schedule, reason);
    }

    // Either we're not donating or the beneficiary disappeared.
    // Either way clear any pending information
    scheduler_data.m_pending_beneficiary = nullptr;
    scheduler_data.m_pending_donate_reason = nullptr;

    quick_sort(sorted_runnables, [](auto& a, auto& b) { return a->effective_priority() >= b->effective_priority(); });

    for (auto* thread : sorted_runnables) {
        if (thread->process().exec_tid() && thread->process().exec_tid() != thread->tid())
            continue;

        ASSERT(thread->state() == Thread::Runnable || thread->state() == Thread::Running);

        if (!thread_to_schedule) {
            thread->m_extra_priority = 0;
            thread_to_schedule = thread;
        } else {
            thread->m_extra_priority++;
        }
    }

    if (!thread_to_schedule)
        thread_to_schedule = Processor::current().idle_thread();

#ifdef SCHEDULER_DEBUG
    dbg() << "Scheduler[" << Processor::current().id() << "]: Switch to " << *thread_to_schedule << " @ " << String::format("%04x:%08x", thread_to_schedule->tss().cs, thread_to_schedule->tss().eip);
#endif

    // We need to leave our first critical section before switching context,
    // but since we're still holding the scheduler lock we're still in a critical section
    critical.leave();

    return context_switch(thread_to_schedule);
}

bool Scheduler::yield()
{
    InterruptDisabler disabler;
    auto& proc = Processor::current();
    auto& scheduler_data = proc.get_scheduler_data();

    // Clear any pending beneficiary
    scheduler_data.m_pending_beneficiary = nullptr;
    scheduler_data.m_pending_donate_reason = nullptr;

    auto current_thread = Thread::current();
#ifdef SCHEDULER_DEBUG
    dbg() << "Scheduler[" << proc.id() << "]: yielding thread " << *current_thread << " in_irq: " << proc.in_irq();
#endif
    ASSERT(current_thread != nullptr);
    if (proc.in_irq() || proc.in_critical()) {
        // If we're handling an IRQ we can't switch context, or we're in
        // a critical section where we don't want to switch contexts, then
        // delay until exiting the trap or critical section
        proc.invoke_scheduler_async();
        return false;
    }

    if (!Scheduler::pick_next())
        return false;
#ifdef SCHEDULER_DEBUG
    dbg() << "Scheduler[" << Processor::current().id() << "]: yield returns to thread " << *current_thread << " in_irq: " << Processor::current().in_irq();
#endif
    return true;
}

bool Scheduler::donate_to_and_switch(Thread* beneficiary, const char* reason)
{
    ASSERT(g_scheduler_lock.own_lock());

    auto& proc = Processor::current();
    ASSERT(proc.in_critical() == 1);

    (void)reason;
    unsigned ticks_left = Thread::current()->ticks_left();
    if (!beneficiary || beneficiary->state() != Thread::Runnable || ticks_left <= 1)
        return Scheduler::yield();

    unsigned ticks_to_donate = min(ticks_left - 1, time_slice_for(*beneficiary));
#ifdef SCHEDULER_DEBUG
    dbg() << "Scheduler[" << proc.id() << "]: Donating " << ticks_to_donate << " ticks to " << *beneficiary << ", reason=" << reason;
#endif
    beneficiary->set_ticks_left(ticks_to_donate);

    return Scheduler::context_switch(beneficiary);
}

bool Scheduler::donate_to(RefPtr<Thread>& beneficiary, const char* reason)
{
    ASSERT(beneficiary);

    if (beneficiary == Thread::current())
        return Scheduler::yield();

    // Set the m_in_scheduler flag before acquiring the spinlock. This
    // prevents a recursive call into Scheduler::invoke_async upon
    // leaving the scheduler lock.
    ScopedCritical critical;
    auto& proc = Processor::current();
    auto& scheduler_data = proc.get_scheduler_data();
    scheduler_data.m_in_scheduler = true;
    ScopeGuard guard(
        []() {
            // We may be on a different processor after we got switched
            // back to this thread!
            auto& scheduler_data = Processor::current().get_scheduler_data();
            ASSERT(scheduler_data.m_in_scheduler);
            scheduler_data.m_in_scheduler = false;
        });

    ASSERT(!proc.in_irq());

    if (proc.in_critical() > 1) {
        scheduler_data.m_pending_beneficiary = beneficiary->make_weak_ptr(); // Save the beneficiary
        scheduler_data.m_pending_donate_reason = reason;
        proc.invoke_scheduler_async();
        return false;
    }

    ScopedSpinLock lock(g_scheduler_lock);

    // "Leave" the critical section before switching context. Since we
    // still hold the scheduler lock, we're not actually leaving it.
    // Processor::switch_context expects Processor::in_critical() to be 1
    critical.leave();
    donate_to_and_switch(beneficiary, reason);
    return false;
}

bool Scheduler::context_switch(Thread* thread)
{
    thread->set_ticks_left(time_slice_for(*thread));
    thread->did_schedule();

    auto from_thread = Thread::current();
    if (from_thread == thread)
        return false;

    if (from_thread) {
        // If the last process hasn't blocked (still marked as running),
        // mark it as runnable for the next round.
        if (from_thread->state() == Thread::Running)
            from_thread->set_state(Thread::Runnable);

#ifdef LOG_EVERY_CONTEXT_SWITCH
        dbg() << "Scheduler[" << Processor::current().id() << "]: " << *from_thread << " -> " << *thread << " [" << thread->priority() << "] " << String::format("%w", thread->tss().cs) << ":" << String::format("%x", thread->tss().eip);
#endif
    }

    auto& proc = Processor::current();
    if (!thread->is_initialized()) {
        proc.init_context(*thread, false);
        thread->set_initialized(true);
    }
    thread->set_state(Thread::Running);

    // Mark it as active because we are using this thread. This is similar
    // to comparing it with Processor::current_thread, but when there are
    // multiple processors there's no easy way to check whether the thread
    // is actually still needed. This prevents accidental finalization when
    // a thread is no longer in Running state, but running on another core.
    thread->set_active(true);

    proc.switch_context(from_thread, thread);

    // NOTE: from_thread at this point reflects the thread we were
    // switched from, and thread reflects Thread::current()
    enter_current(*from_thread);
    ASSERT(thread == Thread::current());

    return true;
}

void Scheduler::enter_current(Thread& prev_thread)
{
    ASSERT(g_scheduler_lock.is_locked());
    prev_thread.set_active(false);
    if (prev_thread.state() == Thread::Dying) {
        // If the thread we switched from is marked as dying, then notify
        // the finalizer. Note that as soon as we leave the scheduler lock
        // the finalizer may free from_thread!
        notify_finalizer();
    }
}

void Scheduler::leave_on_first_switch(u32 flags)
{
    // This is called when a thread is switched into for the first time.
    // At this point, enter_current has already be called, but because
    // Scheduler::context_switch is not in the call stack we need to
    // clean up and release locks manually here
    g_scheduler_lock.unlock(flags);
    auto& scheduler_data = Processor::current().get_scheduler_data();
    ASSERT(scheduler_data.m_in_scheduler);
    scheduler_data.m_in_scheduler = false;
}

void Scheduler::prepare_after_exec()
{
    // This is called after exec() when doing a context "switch" into
    // the new process. This is called from Processor::assume_context
    ASSERT(g_scheduler_lock.own_lock());
    auto& scheduler_data = Processor::current().get_scheduler_data();
    ASSERT(!scheduler_data.m_in_scheduler);
    scheduler_data.m_in_scheduler = true;
}

void Scheduler::prepare_for_idle_loop()
{
    // This is called when the CPU finished setting up the idle loop
    // and is about to run it. We need to acquire he scheduler lock
    ASSERT(!g_scheduler_lock.own_lock());
    g_scheduler_lock.lock();
    auto& scheduler_data = Processor::current().get_scheduler_data();
    ASSERT(!scheduler_data.m_in_scheduler);
    scheduler_data.m_in_scheduler = true;
}

Process* Scheduler::colonel()
{
    ASSERT(s_colonel_process);
    return s_colonel_process;
}

void Scheduler::initialize()
{
    ASSERT(&Processor::current() != nullptr); // sanity check

    RefPtr<Thread> idle_thread;
    g_scheduler_data = new SchedulerData;
    g_finalizer_wait_queue = new WaitQueue;

    g_finalizer_has_work.store(false, AK::MemoryOrder::memory_order_release);
    s_colonel_process = &Process::create_kernel_process(idle_thread, "colonel", idle_loop, 1).leak_ref();
    ASSERT(s_colonel_process);
    ASSERT(idle_thread);
    idle_thread->set_priority(THREAD_PRIORITY_MIN);
    idle_thread->set_name(StringView("idle thread #0"));

    set_idle_thread(idle_thread);
}

void Scheduler::set_idle_thread(Thread* idle_thread)
{
    Processor::current().set_idle_thread(*idle_thread);
    Processor::current().set_current_thread(*idle_thread);
}

Thread* Scheduler::create_ap_idle_thread(u32 cpu)
{
    ASSERT(cpu != 0);
    // This function is called on the bsp, but creates an idle thread for another AP
    ASSERT(Processor::current().id() == 0);

    ASSERT(s_colonel_process);
    Thread* idle_thread = s_colonel_process->create_kernel_thread(idle_loop, THREAD_PRIORITY_MIN, String::format("idle thread #%u", cpu), 1 << cpu, false);
    ASSERT(idle_thread);
    return idle_thread;
}

void Scheduler::timer_tick(const RegisterState& regs)
{
    ASSERT_INTERRUPTS_DISABLED();
    ASSERT(Processor::current().in_irq());

    auto current_thread = Processor::current().current_thread();
    if (!current_thread)
        return;

    bool is_bsp = Processor::current().id() == 0;
    if (!is_bsp)
        return; // TODO: This prevents scheduling on other CPUs!
    if (is_bsp) {
        // TODO: We should probably move this out of the scheduler
        ++g_uptime;

        g_timeofday = TimeManagement::now_as_timeval();
    }

    if (current_thread->process().is_profiling()) {
        SmapDisabler disabler;
        auto backtrace = current_thread->raw_backtrace(regs.ebp, regs.eip);
        auto& sample = Profiling::next_sample_slot();
        sample.pid = current_thread->process().pid();
        sample.tid = current_thread->tid();
        sample.timestamp = g_uptime;
        for (size_t i = 0; i < min(backtrace.size(), Profiling::max_stack_frame_count); ++i) {
            sample.frames[i] = backtrace[i];
        }
    }

    if (is_bsp)
        TimerQueue::the().fire();

    if (current_thread->tick())
        return;

    ASSERT_INTERRUPTS_DISABLED();
    ASSERT(Processor::current().in_irq());
    Processor::current().invoke_scheduler_async();
}

void Scheduler::invoke_async()
{
    ASSERT_INTERRUPTS_DISABLED();
    auto& proc = Processor::current();
    ASSERT(!proc.in_irq());

    // Since this function is called when leaving critical sections (such
    // as a SpinLock), we need to check if we're not already doing this
    // to prevent recursion
    if (!proc.get_scheduler_data().m_in_scheduler)
        pick_next();
}

void Scheduler::notify_finalizer()
{
    if (g_finalizer_has_work.exchange(true, AK::MemoryOrder::memory_order_acq_rel) == false)
        g_finalizer_wait_queue->wake_all();
}

void Scheduler::idle_loop()
{
    dbg() << "Scheduler[" << Processor::current().id() << "]: idle loop running";
    ASSERT(are_interrupts_enabled());

    for (;;) {
        asm("hlt");

        if (Processor::current().id() == 0)
            yield();
    }
}

}