cocos2dx源码分析：定时器Scheduler

cocos2dx的定时器Scheduler实现了每帧都需要调用的函数和有时间间隔和次数的定时器。定时器在Director的init函数中初始化

bool Director::init(void)
{
。。。
_scheduler = new (std::nothrow) Scheduler();
。。。
}

这个scheduler在Node的构造函数中付给了其成员变量_scheduler

_scheduler = _director->getScheduler();
_scheduler->retain();

通过Scheduler的schedule函数可以创建一个定时器

void Scheduler::schedule(SEL_SCHEDULE selector, Ref *target, float interval, unsigned int repeat, float delay, bool paused)
{
    CCASSERT(target, "Argument target must be non-nullptr");

    tHashTimerEntry *element = nullptr;
    // 在哈希表中查找target的定时器
    HASH_FIND_PTR(_hashForTimers, &target, element);

    if (! element)
    {
        // 没找到则创建一个
        element = (tHashTimerEntry *)calloc(sizeof(*element), 1);
        element->target = target;

        HASH_ADD_PTR(_hashForTimers, target, element);

        // Is this the 1st element ? Then set the pause level to all the selectors of this target
        element->paused = paused;
    }
    else
    {
        CCASSERT(element->paused == paused, "element's paused should be paused.");
    }

    if (element->timers == nullptr)
    {
        // 还没有任何定时器，创建一个数组
        element->timers = ccArrayNew(10);
    }
    else
    {
        // 不能有重复的定时器，遍历检查
        for (int i = 0; i < element->timers->num; ++i)
        {
            TimerTargetSelector *timer = dynamic_cast<TimerTargetSelector*>(element->timers->arr[i]);

            if (timer && selector == timer->getSelector())
            {
                CCLOG("CCScheduler#scheduleSelector. Selector already scheduled. Updating interval from: %.4f to %.4f", timer->getInterval(), interval);
                timer->setInterval(interval);
                return;
            }
        }
        ccArrayEnsureExtraCapacity(element->timers, 1);
    }
    // 创建定时器
    TimerTargetSelector *timer = new (std::nothrow) TimerTargetSelector();
    timer->initWithSelector(this, selector, target, interval, repeat, delay);
    ccArrayAppendObject(element->timers, timer);
    timer->release();
}

创建每一帧都需要调用的定时器

void Scheduler::schedulePerFrame(const ccSchedulerFunc& callback, void *target, int priority, bool paused)
{
    tHashUpdateEntry *hashElement = nullptr;
    // 在哈希表中查找目标的定时器
    HASH_FIND_PTR(_hashForUpdates, &target, hashElement);
    if (hashElement)
    {
        // check if priority has changed
        if ((*hashElement->list)->priority != priority)
        {
            if (_updateHashLocked)
            {
                CCLOG("warning: you CANNOT change update priority in scheduled function");
                hashElement->entry->markedForDeletion = false;
                hashElement->entry->paused = paused;
                return;
            }
            else
            {
                // will be added again outside if (hashElement).
                unscheduleUpdate(target);
            }
        }
        else
        {
            hashElement->entry->markedForDeletion = false;
            hashElement->entry->paused = paused;
            return;
        }
    }

    // most of the updates are going to be 0, that's way there
    // is an special list for updates with priority 0
    // 按照优先级不同，同时添加到不同的链表和哈希表_hashForUpdates中
    if (priority == 0)
    {
        appendIn(&_updates0List, callback, target, paused);
    }
    else if (priority < 0)
    {
        priorityIn(&_updatesNegList, callback, target, priority, paused);
    }
    else
    {
        // priority > 0
        priorityIn(&_updatesPosList, callback, target, priority, paused);
    }
}

在Director的drawScene函数中，如果Director未暂停，则触发定时器

void Director::drawScene()
{
。。。
 if (! _paused)
    {
        _eventDispatcher->dispatchEvent(_eventBeforeUpdate);
        _scheduler->update(_deltaTime);
        _eventDispatcher->dispatchEvent(_eventAfterUpdate);
    }
。。。
}

定时器update，大致过程是，先按优先级触发每帧都调用的定时器，然后调用其它定时器，最后删除标记为删除的定时器

void Scheduler::update(float dt)
{
    _updateHashLocked = true;

    if (_timeScale != 1.0f)
    {
        dt *= _timeScale;
    }

    //
    // Selector callbacks
    //

    // Iterate over all the Updates' selectors
    tListEntry *entry, *tmp;

    // updates with priority < 0
    DL_FOREACH_SAFE(_updatesNegList, entry, tmp)
    {
        if ((! entry->paused) && (! entry->markedForDeletion))
        {
            entry->callback(dt);
        }
    }

    // updates with priority == 0
    DL_FOREACH_SAFE(_updates0List, entry, tmp)
    {
        if ((! entry->paused) && (! entry->markedForDeletion))
        {
            entry->callback(dt);
        }
    }

    // updates with priority > 0
    DL_FOREACH_SAFE(_updatesPosList, entry, tmp)
    {
        if ((! entry->paused) && (! entry->markedForDeletion))
        {
            entry->callback(dt);
        }
    }

    // Iterate over all the custom selectors
    for (tHashTimerEntry *elt = _hashForTimers; elt != nullptr; )
    {
        _currentTarget = elt;
        _currentTargetSalvaged = false;

        if (! _currentTarget->paused)
        {
            // The 'timers' array may change while inside this loop
            for (elt->timerIndex = 0; elt->timerIndex < elt->timers->num; ++(elt->timerIndex))
            {
                elt->currentTimer = (Timer*)(elt->timers->arr[elt->timerIndex]);
                elt->currentTimerSalvaged = false;

                elt->currentTimer->update(dt);

                if (elt->currentTimerSalvaged)
                {
                    // The currentTimer told the remove itself. To prevent the timer from
                    // accidentally deallocating itself before finishing its step, we retained
                    // it. Now that step is done, it's safe to release it.
                    elt->currentTimer->release();
                }

                elt->currentTimer = nullptr;
            }
        }

        // elt, at this moment, is still valid
        // so it is safe to ask this here (issue #490)
        elt = (tHashTimerEntry *)elt->hh.next;

        // only delete currentTarget if no actions were scheduled during the cycle (issue #481)
        if (_currentTargetSalvaged && _currentTarget->timers->num == 0)
        {
            removeHashElement(_currentTarget);
        }
    }

    // delete all updates that are marked for deletion
    // updates with priority < 0
    DL_FOREACH_SAFE(_updatesNegList, entry, tmp)
    {
        if (entry->markedForDeletion)
        {
            this->removeUpdateFromHash(entry);
        }
    }

    // updates with priority == 0
    DL_FOREACH_SAFE(_updates0List, entry, tmp)
    {
        if (entry->markedForDeletion)
        {
            this->removeUpdateFromHash(entry);
        }
    }

    // updates with priority > 0
    DL_FOREACH_SAFE(_updatesPosList, entry, tmp)
    {
        if (entry->markedForDeletion)
        {
            this->removeUpdateFromHash(entry);
        }
    }

    _updateHashLocked = false;
    _currentTarget = nullptr;

#if CC_ENABLE_SCRIPT_BINDING
    //
    // Script callbacks
    //

    // Iterate over all the script callbacks
    if (!_scriptHandlerEntries.empty())
    {
        for (auto i = _scriptHandlerEntries.size() - 1; i >= 0; i--)
        {
            SchedulerScriptHandlerEntry* eachEntry = _scriptHandlerEntries.at(i);
            if (eachEntry->isMarkedForDeletion())
            {
                _scriptHandlerEntries.erase(i);
            }
            else if (!eachEntry->isPaused())
            {
                eachEntry->getTimer()->update(dt);
            }
        }
    }
#endif
    //
    // Functions allocated from another thread
    //

    // Testing size is faster than locking / unlocking.
    // And almost never there will be functions scheduled to be called.
    if( !_functionsToPerform.empty() ) {
        _performMutex.lock();
        // fixed #4123: Save the callback functions, they must be invoked after '_performMutex.unlock()', otherwise if new functions are added in callback, it will cause thread deadlock.
        auto temp = _functionsToPerform;
        _functionsToPerform.clear();
        _performMutex.unlock();
        for( const auto &function : temp ) {
            function();
        }

    }
}