timersmanager 解析

最近在看crtmp源代碼，看到timersmanager 子產品時感覺很難了解，花了不少時間反複思考該子產品

的邏輯，現在思考的結果記錄下來，友善以後查閱。

構造函數中将處理時間方法傳進來，将_lastTime指派為目前時間，将目前slot Index設定為0，Slot指針

賦為空，slot數目賦為0。slot可以了解為槽。

TimersManager::TimersManager(ProcessTimerEvent processTimerEvent) {
	_processTimerEvent = processTimerEvent;
	_lastTime = time(NULL);
	_currentSlotIndex = 0;
	_pSlots = NULL;
	_slotsCount = 0;
}
      

　　析構時釋放掉slot，無需多解釋。

TimersManager::~TimersManager() {
    if (_pSlots != NULL)
        delete[] _pSlots;
}      

移除處理事件方法,将id為eventTimerId的事件處理方法從所有的slot中移除掉

void TimersManager::RemoveTimer(uint32_t eventTimerId) {
    for (uint32_t i = 0; i < _slotsCount; i++) {
        if (MAP_HAS1(_pSlots[i].timers, eventTimerId)) {
            _pSlots[i].timers.erase(eventTimerId);
        }
    }
}
      

void TimersManager::AddTimer(TimerEvent& timerEvent) {
    UpdatePeriods(timerEvent.period);
    uint32_t min = 999999999;
    uint32_t startIndex = 0;
    for (uint32_t i = 0; i < _slotsCount; i++) {
        if (min > _pSlots[i].timers.size()) {
            startIndex = i;
            min = _pSlots[i].timers.size();
        }
    }
    while (!MAP_HAS1(_pSlots[startIndex % _slotsCount].timers, timerEvent.id)) {
        _pSlots[startIndex % _slotsCount].timers[timerEvent.id] = timerEvent;
        startIndex += timerEvent.period;
    }
}

void TimersManager::TimeElapsed(uint64_t currentTime) {
    int64_t delta = currentTime - _lastTime;
    _lastTime = currentTime;

    if (delta <= 0 || _slotsCount == 0)
        return;

    for (int32_t i = 0; i < delta; i++) {
        //每間隔period個槽裡都會存放TimeEvent，比如某個TimeEvent的period為100，delta為9，最多
          TimeEvent對應的事件隻執行一次。
        FOR_MAP(_pSlots[_currentSlotIndex % _slotsCount].timers, uint32_t, TimerEvent, j) {
            _processTimerEvent(MAP_VAL(j));
        }
        _currentSlotIndex++;
    }
}


void TimersManager::UpdatePeriods(uint32_t period) {
//如果 TimeEvent周期已經存在直接傳回
    if (MAP_HAS1(_periodsMap, period))
        return;
    _periodsMap[period] = period;
//将TimeEvent 周期放在period vector中
    ADD_VECTOR_END(_periodsVector, period);
//計算所有period的最小公倍數，比如之前period為4，新period為3，總Slot Count 為4 * 3 = 12
    uint32_t newSlotsCount = LCM(_periodsVector, 0);
    if (newSlotsCount == 0)
        newSlotsCount = period;
    if (newSlotsCount == _slotsCount)
        return;
    Slot *pNewSlots = new Slot[newSlotsCount];
    if (_slotsCount > 0) {
//将Slot Count增加到30，本質上試講之前的slot複制5份
        for (uint32_t i = 0; i < newSlotsCount; i++) {
            pNewSlots[i] = _pSlots[i % _slotsCount];
        }
        delete[] _pSlots;
    }
    _pSlots = pNewSlots;
    _slotsCount = newSlotsCount;
}

GCD最大公約數，LCM 求最大公倍數
uint32_t TimersManager::GCD(uint32_t a, uint32_t b) {
    while (b != 0) {
        uint32_t t = b;
        b = a % b;
        a = t;
    }
    return a;
}

uint32_t TimersManager::LCM(uint32_t a, uint32_t b) {
    if (a == 0 || b == 0)
        return 0;
    uint32_t result = a * b / GCD(a, b);
    FINEST("a: %u; b: %u; r: %u", a, b, result);
    return result;
}

uint32_t TimersManager::GCD(vector<uint32_t> numbers, uint32_t startIndex) {
    if (numbers.size() <= 1)
        return 0;
    if (numbers.size() <= startIndex)
        return 0;
    if (numbers.size() - startIndex > 2) {
        return GCD(numbers[startIndex], GCD(numbers, startIndex + 1));
    } else {
        return GCD(numbers[startIndex], numbers[startIndex + 1]);
    }
}

uint32_t TimersManager::LCM(vector<uint32_t> numbers, uint32_t startIndex) {
    if (numbers.size() <= 1)
        return 0;
    if (numbers.size() <= startIndex)
        return 0;
    if (numbers.size() - startIndex > 2) {
        return LCM(numbers[startIndex], LCM(numbers, startIndex + 1));
    } else {
        return LCM(numbers[startIndex], numbers[startIndex + 1]);
    }
}


/*
 *
 * TimersManager tm(NULL);
    TimerEvent t1 = {2, 1, NULL};
    TimerEvent t2 = {3, 2, NULL};
    TimerEvent t3 = {3, 3, NULL};
    TimerEvent t4 = {4, 4, NULL};
    TimerEvent t5 = {3, 5, NULL};
    TimerEvent t6 = {2, 6, NULL};
    TimerEvent t7 = {4, 7, NULL};

    tm.AddTimer(t1);
    tm.AddTimer(t2);
    tm.AddTimer(t3);
    tm.AddTimer(t4);
    tm.AddTimer(t5);
    tm.AddTimer(t6);
    tm.AddTimer(t7);
 *
 * */
      

 如下圖所示：第一個TimeEvent的周期為4，是以slot數目為4,也就是圖1中的前4個slot。添加第二個TimeEvent的周期為3，UpdatePeriods

方法将前4個slot複制3份得到12個slot，這樣TimeEvent1被放到1，5，9個slot中。接下來AddTimer方法會将TimeEvent2添加到slot中：第一

個添加的slot是slot_2,因為這個slot的TimeEvent總數為0，接下來添加的solt分别是slot_5,slot_8,slot_11，如果繼續添加下去是（11 + 3）%

3 = 2，但slot_2已經添加過，各槽添加TimeEvent2結束。作者将slot總槽書設計為所有的period最小公倍數，在這裡發送作用了。 

                                                                                      圖1