webrtc/modules/audio_conference_mixer/source/time_scheduler.cc

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "webrtc/base/timeutils.h"
#include "webrtc/modules/audio_conference_mixer/source/time_scheduler.h"
#include "webrtc/system_wrappers/include/critical_section_wrapper.h"

namespace webrtc {
TimeScheduler::TimeScheduler(const int64_t periodicityInMs)
    : _crit(CriticalSectionWrapper::CreateCriticalSection()),
      _isStarted(false),
      _lastPeriodMark(),
      _periodicityInMs(periodicityInMs),
      _periodicityInTicks(periodicityInMs * rtc::kNumNanosecsPerMillisec),
      _missedPeriods(0)
 {
 }

TimeScheduler::~TimeScheduler()
{
    delete _crit;
}

int32_t TimeScheduler::UpdateScheduler()
{
    CriticalSectionScoped cs(_crit);
    if(!_isStarted)
    {
        _isStarted = true;
        _lastPeriodMark = rtc::TimeNanos();
        return 0;
    }
    // Don't perform any calculations until the debt of pending periods have
    // been worked off.
    if(_missedPeriods > 0)
    {
        _missedPeriods--;
        return 0;
    }

    // Calculate the time that has past since previous call to this function.
    int64_t tickNow = rtc::TimeNanos();
    int64_t amassedTicks = tickNow - _lastPeriodMark;
    int64_t amassedMs = amassedTicks / rtc::kNumNanosecsPerMillisec;

    // Calculate the number of periods the time that has passed correspond to.
    int64_t periodsToClaim = amassedMs / _periodicityInMs;

    // One period will be worked off by this call. Make sure that the number of
    // pending periods don't end up being negative (e.g. if this function is
    // called to often).
    if(periodsToClaim < 1)
    {
        periodsToClaim = 1;
    }

    // Update the last period mark without introducing any drifting.
    // Note that if this fuunction is called to often _lastPeriodMark can
    // refer to a time in the future which in turn will yield TimeToNextUpdate
    // that is greater than the periodicity
    for(int64_t i = 0; i < periodsToClaim; i++)
    {
        _lastPeriodMark += _periodicityInTicks;
    }

    // Update the total amount of missed periods note that we have processed
    // one period hence the - 1
    _missedPeriods += periodsToClaim - 1;
    return 0;
}

int32_t TimeScheduler::TimeToNextUpdate(
    int64_t& updateTimeInMS) const
{
    CriticalSectionScoped cs(_crit);
    // Missed periods means that the next UpdateScheduler() should happen
    // immediately.
    if(_missedPeriods > 0)
    {
        updateTimeInMS = 0;
        return 0;
    }

    // Calculate the time (in ms) that has past since last call to
    // UpdateScheduler()
    int64_t tickNow = rtc::TimeNanos();
    int64_t ticksSinceLastUpdate = tickNow - _lastPeriodMark;
    const int64_t millisecondsSinceLastUpdate =
      ticksSinceLastUpdate / rtc::kNumNanosecsPerMillisec;

    updateTimeInMS = _periodicityInMs - millisecondsSinceLastUpdate;
    updateTimeInMS =  (updateTimeInMS < 0) ? 0 : updateTimeInMS;
    return 0;
}
}  // namespace webrtc