muduo源码剖析--Poller/EpollPoller

Poller类

Poller是EpollPoller和poll的基类实现，是一个虚基类，主要封装了IO多路复用的核心接口

// muduo库中多路事件分发器的核心IO复用模块
class Poller
{
public:
    using ChannelList = std::vector<Channel *>;

    Poller(EventLoop *loop);
    virtual ~Poller() = default;

    // 给所有IO复用保留统一的接口
    virtual Timestamp poll(int timeoutMs, ChannelList *activeChannels) = 0; //EventLoop对象通过这个函数拿到具体发生关心事件的通道有哪些
    virtual void updateChannel(Channel *channel) = 0; //修改通道关心的事件
    virtual void removeChannel(Channel *channel) = 0; //移除通道关心的事件

    

protected:
    // map的key:sockfd value:sockfd所属的channel通道类型
    using ChannelMap = std::unordered_map<int, Channel *>;
    ChannelMap channels_;

private:
    EventLoop *ownerLoop_; // 定义Poller所属的事件循环EventLoop
};

poller类可以判断是否监听了某个通道（实际上看EventLoop对象是否绑定了该通道），也即hasChannel函数

// 判断参数channel是否在当前的Poller当中
    bool hasChannel(Channel *channel) const;

	bool Poller::hasChannel(Channel *channel) const
{
    auto it = channels_.find(channel->fd());
    return it != channels_.end() && it->second == channel;
}
    // EventLoop可以通过该接口获取默认的IO复用的具体实现， 得到epoll实例亦或是poll实例
    static Poller *newDefaultPoller(EventLoop *loop);

EpollPoller类

继承至Poller类，具体实现epoll多路复用的子类

/**
 * epoll的使用:
 * 1. epoll_create
 * 2. epoll_ctl (add, mod, del)
 * 3. epoll_wait
 **/

class Channel;

class EPollPoller : public Poller
{
public:
    EPollPoller(EventLoop *loop);
    ~EPollPoller() override;

    // 重写基类Poller的抽象方法
    Timestamp poll(int timeoutMs, ChannelList *activeChannels) override; //epoll模式下，EventLoop对象通过这个函数拿到具体发生关心事件的通道有哪些
    void updateChannel(Channel *channel) override;
    void removeChannel(Channel *channel) override;

private:
    static const int kInitEventListSize = 16; //初始化事件个数

    // 填写活跃的连接
    void fillActiveChannels(int numEvents, ChannelList *activeChannels) const;
    // 更新channel通道 其实就是调用epoll_ctl
    void update(int operation, Channel *channel);

    using EventList = std::vector<epoll_event>; // C++中可以省略struct 直接写epoll_event即可

    int epollfd_;      // epoll_create创建返回的fd保存在epollfd_中
    EventList events_; // 用于存放epoll_wait返回的所有发生的事件的文件描述符事件集
};

EpollPoller构造：首先调用基类Poller的构造绑定EventLoop对象，再通过epoll_create1方法构造epollfd， 并初始化相应监听事件的数量

EPollPoller::EPollPoller(EventLoop *loop)
    : Poller(loop)
    , epollfd_(::epoll_create1(EPOLL_CLOEXEC))
    , events_(kInitEventListSize) // vector(16)
{
    if (epollfd_ < 0)
    {
        LOG_FATAL("epoll_create error:%d \n", errno);
    }
}

epoll的io多路复用实现，即重写基类Poller的poll接口

Timestamp EPollPoller::poll(int timeoutMs, ChannelList *activeChannels)
{
    // 由于频繁调用poll 实际上应该用LOG_DEBUG输出日志更为合理 当遇到并发场景 关闭DEBUG日志提升效率
    LOG_INFO("func=%s => fd total count:%lu\n", __FUNCTION__, channels_.size());

	//调用epoll_wait方法监听事件，返回发生活跃事件fd的个数
    int numEvents = ::epoll_wait(epollfd_, &*events_.begin(), static_cast<int>(events_.size()), timeoutMs);
    int saveErrno = errno;
    Timestamp now(Timestamp::now());

    if (numEvents > 0)
    {
        LOG_INFO("%d events happend\n", numEvents); // LOG_DEBUG最合理
        fillActiveChannels(numEvents, activeChannels);  //填充活跃fd对应的通道，并放入活跃通道列表中
        if (numEvents == events_.size()) // 扩容操作
        {
            events_.resize(events_.size() * 2); //每次2倍扩容
        }
    }
    else if (numEvents == 0)
    {
        LOG_DEBUG("%s timeout!\n", __FUNCTION__);
    }
    else
    {
        if (saveErrno != EINTR)
        {
            errno = saveErrno;
            LOG_ERROR("EPollPoller::poll() error!");
        }
    }
    return now;
}

// 填写活跃的连接
void EPollPoller::fillActiveChannels(int numEvents, ChannelList *activeChannels) const
{
    for (int i = 0; i < numEvents; ++i)
    {
        Channel *channel = static_cast<Channel *>(events_[i].data.ptr);
        channel->set_revents(events_[i].events);
        activeChannels->push_back(channel); // EventLoop就拿到了它的Poller给它返回的所有发生事件的channel列表了
    }
}

与之绑定的EventLoop对象调用update()和remove()方法实际上上是调用EpollPoller的updateChannel()和removeChannel()方法。注意每添加一个新的fd，channels都会将fd与通道记录在map中，每删除一个fd，都会将这个fd对应的map映射删除。

const int kNew = -1;    // 某个channel还没添加至Poller          // channel的成员index_初始化为-1
const int kAdded = 1;   // 某个channel已经添加至Poller
const int kDeleted = 2; // 某个channel已经从Poller删除

// 调用流程：channel update remove => EventLoop updateChannel removeChannel => Poller updateChannel removeChannel
void EPollPoller::updateChannel(Channel *channel)
{
    const int index = channel->index();
    LOG_INFO("func=%s => fd=%d events=%d index=%d\n", __FUNCTION__, channel->fd(), channel->events(), index);

    if (index == kNew || index == kDeleted)
    {
        if (index == kNew)
        {
            int fd = channel->fd();
            channels_[fd] = channel;  //将新的fd设置进map
        }
        else // index == kAdd
        {
        }
        channel->set_index(kAdded);
        update(EPOLL_CTL_ADD, channel);
    }
    else // channel已经在Poller中注册过了
    {
        int fd = channel->fd();
        if (channel->isNoneEvent())
        {
            update(EPOLL_CTL_DEL, channel);
            channel->set_index(kDeleted);
        }
        else
        {
            update(EPOLL_CTL_MOD, channel);
        }
    }
}

// 从Poller中删除channel
void EPollPoller::removeChannel(Channel *channel)
{
    int fd = channel->fd();
    channels_.erase(fd); //删除之后channel_map需要移除对应的fd

    LOG_INFO("func=%s => fd=%d\n", __FUNCTION__, fd);

    int index = channel->index();
    if (index == kAdded)
    {
        update(EPOLL_CTL_DEL, channel);
    }
    channel->set_index(kNew);
}

而实际上的调用还封装了一层：Poller::updateChannel/removeChannel -> Poller::update()
Poller::update()才是真正的修改通道所绑定的fd的事件

// 更新channel通道 其实就是调用epoll_ctl add/mod/del
void EPollPoller::update(int operation, Channel *channel)
{
    epoll_event event;
    ::memset(&event, 0, sizeof(event));

    int fd = channel->fd();

    event.events = channel->events();
    event.data.fd = fd;
    event.data.ptr = channel; //绑定fd对应的Channel

    if (::epoll_ctl(epollfd_, operation, fd, &event) < 0)
    {
        if (operation == EPOLL_CTL_DEL)
        {
            LOG_ERROR("epoll_ctl del error:%d\n", errno);
        }
        else
        {
            LOG_FATAL("epoll_ctl add/mod error:%d\n", errno);
        }
    }
}

EPollPoller释放操作，关系epollfd即可

EPollPoller::~EPollPoller()
{
    ::close(epollfd_);
}