ladybird/Kernel/TimerQueue.cpp

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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Singleton.h>
#include <AK/Time.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Sections.h>
#include <Kernel/Time/TimeManagement.h>
#include <Kernel/TimerQueue.h>
namespace Kernel {
static Singleton<TimerQueue> s_the;
static Spinlock g_timerqueue_lock { LockRank::None };
Time Timer::remaining() const
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{
return m_remaining;
}
Time Timer::now(bool is_firing) const
{
// NOTE: If is_firing is true then TimePrecision::Precise isn't really useful here.
// We already have a quite precise time stamp because we just updated the time in the
// interrupt handler. In those cases, just use coarse timestamps.
auto clock_id = m_clock_id;
if (is_firing) {
switch (clock_id) {
case CLOCK_MONOTONIC:
clock_id = CLOCK_MONOTONIC_COARSE;
break;
case CLOCK_MONOTONIC_RAW:
// TODO: use a special CLOCK_MONOTONIC_RAW_COARSE like mechanism here
break;
case CLOCK_REALTIME:
clock_id = CLOCK_REALTIME_COARSE;
break;
default:
break;
}
}
return TimeManagement::the().current_time(clock_id);
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}
TimerQueue& TimerQueue::the()
{
return *s_the;
}
UNMAP_AFTER_INIT TimerQueue::TimerQueue()
{
m_ticks_per_second = TimeManagement::the().ticks_per_second();
}
bool TimerQueue::add_timer_without_id(NonnullLockRefPtr<Timer> timer, clockid_t clock_id, Time const& deadline, Function<void()>&& callback)
{
if (deadline <= TimeManagement::the().current_time(clock_id))
return false;
// Because timer handlers can execute on any processor and there is
// a race between executing a timer handler and cancel_timer() this
// *must* be a LockRefPtr<Timer>. Otherwise, calling cancel_timer() could
// inadvertently cancel another timer that has been created between
// returning from the timer handler and a call to cancel_timer().
timer->setup(clock_id, deadline, move(callback));
SpinlockLocker lock(g_timerqueue_lock);
timer->m_id = 0; // Don't generate a timer id
add_timer_locked(move(timer));
return true;
}
TimerId TimerQueue::add_timer(NonnullLockRefPtr<Timer>&& timer)
{
SpinlockLocker lock(g_timerqueue_lock);
timer->m_id = ++m_timer_id_count;
VERIFY(timer->m_id != 0); // wrapped
auto id = timer->m_id;
add_timer_locked(move(timer));
return id;
}
void TimerQueue::add_timer_locked(NonnullLockRefPtr<Timer> timer)
{
Time timer_expiration = timer->m_expires;
timer->clear_cancelled();
timer->clear_callback_finished();
timer->set_in_use();
auto& queue = queue_for_timer(*timer);
if (queue.list.is_empty()) {
queue.list.append(timer.leak_ref());
queue.next_timer_due = timer_expiration;
} else {
Timer* following_timer = nullptr;
for (auto& t : queue.list) {
if (t.m_expires > timer_expiration) {
following_timer = &t;
break;
}
}
if (following_timer) {
bool next_timer_needs_update = queue.list.first() == following_timer;
queue.list.insert_before(*following_timer, timer.leak_ref());
if (next_timer_needs_update)
queue.next_timer_due = timer_expiration;
} else {
queue.list.append(timer.leak_ref());
}
}
}
bool TimerQueue::cancel_timer(Timer& timer, bool* was_in_use)
{
bool in_use = timer.is_in_use();
if (was_in_use)
*was_in_use = in_use;
// If the timer isn't in use, the cancellation is a no-op.
if (!in_use) {
VERIFY(!timer.m_list_node.is_in_list());
return false;
}
bool did_already_run = timer.set_cancelled();
auto& timer_queue = queue_for_timer(timer);
if (!did_already_run) {
timer.clear_in_use();
SpinlockLocker lock(g_timerqueue_lock);
if (timer_queue.list.contains(timer)) {
// The timer has not fired, remove it
VERIFY(timer.ref_count() > 1);
remove_timer_locked(timer_queue, timer);
return true;
}
// The timer was queued to execute but hasn't had a chance
// to run. In this case, it should still be in m_timers_executing
// and we don't need to spin. It still holds a reference
// that will be dropped when it does get a chance to run,
// but since we called set_cancelled it will only drop its reference
VERIFY(m_timers_executing.contains(timer));
m_timers_executing.remove(timer);
return true;
}
// At this point the deferred call is queued and is being executed
// on another processor. We need to wait until it's complete!
while (!timer.is_callback_finished())
Processor::wait_check();
return false;
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}
void TimerQueue::remove_timer_locked(Queue& queue, Timer& timer)
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{
bool was_next_timer = (queue.list.first() == &timer);
queue.list.remove(timer);
auto now = timer.now(false);
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if (timer.m_expires > now)
timer.m_remaining = timer.m_expires - now;
if (was_next_timer)
update_next_timer_due(queue);
// Whenever we remove a timer that was still queued (but hasn't been
// fired) we added a reference to it. So, when removing it from the
// queue we need to drop that reference.
timer.unref();
}
void TimerQueue::fire()
{
SpinlockLocker lock(g_timerqueue_lock);
auto fire_timers = [&](Queue& queue) {
auto* timer = queue.list.first();
VERIFY(timer);
VERIFY(queue.next_timer_due == timer->m_expires);
while (timer && timer->now(true) > timer->m_expires) {
queue.list.remove(*timer);
m_timers_executing.append(*timer);
update_next_timer_due(queue);
lock.unlock();
// Defer executing the timer outside of the irq handler
Processor::deferred_call_queue([this, timer]() {
// Check if we were cancelled in between being triggered
// by the timer irq handler and now. If so, just drop
// our reference and don't execute the callback.
if (!timer->set_cancelled()) {
timer->m_callback();
SpinlockLocker lock(g_timerqueue_lock);
m_timers_executing.remove(*timer);
}
timer->clear_in_use();
timer->set_callback_finished();
// Drop the reference we added when queueing the timer
timer->unref();
});
lock.lock();
timer = queue.list.first();
}
};
if (!m_timer_queue_monotonic.list.is_empty())
fire_timers(m_timer_queue_monotonic);
if (!m_timer_queue_realtime.list.is_empty())
fire_timers(m_timer_queue_realtime);
}
void TimerQueue::update_next_timer_due(Queue& queue)
{
VERIFY(g_timerqueue_lock.is_locked());
if (auto* next_timer = queue.list.first())
queue.next_timer_due = next_timer->m_expires;
else
queue.next_timer_due = {};
}
}