1 files changed, 232 insertions, 0 deletions
diff --git a/Kernel/Time/TimerQueue.cpp b/Kernel/Time/TimerQueue.cpp
new file mode 100644
index 0000000000..89546b0c07
--- /dev/null
+++ b/Kernel/Time/TimerQueue.cpp
@@ -0,0 +1,232 @@
+/*
+ * 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/Sections.h>
+#include <Kernel/Tasks/Scheduler.h>
+#include <Kernel/Time/TimeManagement.h>
+#include <Kernel/Time/TimerQueue.h>
+
+namespace Kernel {
+
+static Singleton<TimerQueue> s_the;
+static Spinlock<LockRank::None> g_timerqueue_lock {};
+
+Duration Timer::remaining() const
+{
+    return m_remaining;
+}
+
+Duration 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);
+}
+
+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(NonnullRefPtr<Timer> timer, clockid_t clock_id, Duration 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 RefPtr<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(NonnullRefPtr<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(NonnullRefPtr<Timer> timer)
+{
+    Duration 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;
+}
+
+void TimerQueue::remove_timer_locked(Queue& queue, Timer& timer)
+{
+    bool was_next_timer = (queue.list.first() == &timer);
+    queue.list.remove(timer);
+    auto now = timer.now(false);
+    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 = {};
+}
+
+}