src/core/common/timer.cpp

/*
 *  Copyright (c) 2016, The OpenThread Authors.
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 *
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 *  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.
 *  3. Neither the name of the copyright holder nor the
 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  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
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 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @file
 *   This file implements a multiplexed timer service on top of the alarm abstraction.
 */

#include "timer.hpp"

#include "common/as_core_type.hpp"
#include "common/code_utils.hpp"
#include "common/debug.hpp"
#include "common/instance.hpp"
#include "common/locator_getters.hpp"

namespace ot {

const Timer::Scheduler::AlarmApi TimerMilli::Scheduler::sAlarmMilliApi = {
    &otPlatAlarmMilliStartAt,
    &otPlatAlarmMilliStop,
    &otPlatAlarmMilliGetNow,
};

bool Timer::DoesFireBefore(const Timer &aSecondTimer, Time aNow) const
{
    // Indicates whether the fire time of this timer is strictly
    // before the fire time of a second given timer.

    bool retval;
    bool isBeforeNow = (GetFireTime() < aNow);

    // Check if one timer is before `now` and the other one is not.
    if ((aSecondTimer.GetFireTime() < aNow) != isBeforeNow)
    {
        // One timer is before `now` and the other one is not, so if
        // this timer's fire time is before `now` then the second fire
        // time would be after `now` and this timer would fire before
        // the second timer.

        retval = isBeforeNow;
    }
    else
    {
        // Both timers are before `now` or both are after `now`. Either
        // way the difference is guaranteed to be less than `kMaxDt` so
        // we can safely compare the fire times directly.

        retval = GetFireTime() < aSecondTimer.GetFireTime();
    }

    return retval;
}

void TimerMilli::Start(uint32_t aDelay)
{
    StartAt(GetNow(), aDelay);
}

void TimerMilli::StartAt(TimeMilli aStartTime, uint32_t aDelay)
{
    OT_ASSERT(aDelay <= kMaxDelay);
    FireAt(aStartTime + aDelay);
}

void TimerMilli::FireAt(TimeMilli aFireTime)
{
    mFireTime = aFireTime;
    Get<Scheduler>().Add(*this);
}

void TimerMilli::FireAtIfEarlier(TimeMilli aFireTime)
{
    if (!IsRunning() || (mFireTime > aFireTime))
    {
        FireAt(aFireTime);
    }
}

void TimerMilli::Stop(void)
{
    Get<Scheduler>().Remove(*this);
}

void TimerMilli::RemoveAll(Instance &aInstance)
{
    aInstance.Get<Scheduler>().RemoveAll();
}

void Timer::Scheduler::Add(Timer &aTimer, const AlarmApi &aAlarmApi)
{
    Timer *prev = nullptr;
    Time   now(aAlarmApi.AlarmGetNow());

    Remove(aTimer, aAlarmApi);

    for (Timer &cur : mTimerList)
    {
        if (aTimer.DoesFireBefore(cur, now))
        {
            break;
        }

        prev = &cur;
    }

    if (prev == nullptr)
    {
        mTimerList.Push(aTimer);
        SetAlarm(aAlarmApi);
    }
    else
    {
        mTimerList.PushAfter(aTimer, *prev);
    }
}

void Timer::Scheduler::Remove(Timer &aTimer, const AlarmApi &aAlarmApi)
{
    VerifyOrExit(aTimer.IsRunning());

    if (mTimerList.GetHead() == &aTimer)
    {
        mTimerList.Pop();
        SetAlarm(aAlarmApi);
    }
    else
    {
        IgnoreError(mTimerList.Remove(aTimer));
    }

    aTimer.SetNext(&aTimer);

exit:
    return;
}

void Timer::Scheduler::SetAlarm(const AlarmApi &aAlarmApi)
{
    if (mTimerList.IsEmpty())
    {
        aAlarmApi.AlarmStop(&GetInstance());
    }
    else
    {
        Timer *  timer = mTimerList.GetHead();
        Time     now(aAlarmApi.AlarmGetNow());
        uint32_t remaining;

        remaining = (now < timer->mFireTime) ? (timer->mFireTime - now) : 0;

        aAlarmApi.AlarmStartAt(&GetInstance(), now.GetValue(), remaining);
    }
}

void Timer::Scheduler::ProcessTimers(const AlarmApi &aAlarmApi)
{
    Timer *timer = mTimerList.GetHead();

    if (timer)
    {
        Time now(aAlarmApi.AlarmGetNow());

        if (now >= timer->mFireTime)
        {
            Remove(*timer, aAlarmApi); // `Remove()` will `SetAlarm` for next timer if there is any.
            timer->Fired();
            ExitNow();
        }
    }

    SetAlarm(aAlarmApi);

exit:
    return;
}

void Timer::Scheduler::RemoveAll(const AlarmApi &aAlarmApi)
{
    Timer *timer;

    while ((timer = mTimerList.Pop()) != nullptr)
    {
        timer->SetNext(timer);
    }

    SetAlarm(aAlarmApi);
}

extern "C" void otPlatAlarmMilliFired(otInstance *aInstance)
{
    VerifyOrExit(otInstanceIsInitialized(aInstance));
    AsCoreType(aInstance).Get<TimerMilli::Scheduler>().ProcessTimers();

exit:
    return;
}

#if OPENTHREAD_CONFIG_PLATFORM_USEC_TIMER_ENABLE
const Timer::Scheduler::AlarmApi TimerMicro::Scheduler::sAlarmMicroApi = {
    &otPlatAlarmMicroStartAt,
    &otPlatAlarmMicroStop,
    &otPlatAlarmMicroGetNow,
};

void TimerMicro::Start(uint32_t aDelay)
{
    StartAt(GetNow(), aDelay);
}

void TimerMicro::StartAt(TimeMicro aStartTime, uint32_t aDelay)
{
    OT_ASSERT(aDelay <= kMaxDelay);
    FireAt(aStartTime + aDelay);
}

void TimerMicro::FireAt(TimeMicro aFireTime)
{
    mFireTime = aFireTime;
    Get<Scheduler>().Add(*this);
}

void TimerMicro::Stop(void)
{
    Get<Scheduler>().Remove(*this);
}

void TimerMicro::RemoveAll(Instance &aInstance)
{
    aInstance.Get<Scheduler>().RemoveAll();
}

extern "C" void otPlatAlarmMicroFired(otInstance *aInstance)
{
    VerifyOrExit(otInstanceIsInitialized(aInstance));
    AsCoreType(aInstance).Get<TimerMicro::Scheduler>().ProcessTimers();

exit:
    return;
}
#endif // OPENTHREAD_CONFIG_PLATFORM_USEC_TIMER_ENABLE

} // namespace ot