handy源码阅读（五）：PollerBase类

使用poll内核函数等待事件发生：

struct PollerBase: private noncopyable {
  int64_t id_;
  int lastActive_;
  PollerBase(): lastActive_(-) {
    static std::atomic<int64_t> id();
    id_ = ++id;
  }

  virtual void addChannel(Channel* ch) = ;
  virtual void removeChannel(Channel* ch) = ;
  virtual void updateChannel(Channel* ch) = ;
  virtual ~PollerBase() {};
};

struct PollerEpoll : public PollerBase {
  int fd_;
  std::set<Channel*> liveChannels_;
  struct epoll_event activeEvs_[kMaxEvents];

  PollerEpoll();
  ~PollerEpoll();
  void addChannel(Channel* ch) override;
  void removeChannel(Channel* ch) override;
  void updateChannel(Channel* ch) override;
  void loop_once(int waitMs) override;
};

pollerEpoll的实现主要是使用了epoll类函数。

PollerBase* createPoller() {
  return new PollerEpoll();
}

PollerEpoll::PollerEpoll() {
  fd_ = epoll_create1(EPOLL_CLOEXEC);  //创建一个epoll文件描述符
}

PollerEpoll::~PollerEpoll() {
  while (liveChannels_.size()) {
    (*liveChannels_.begin())->close();  //从poller中移除该通道，关闭通道上的文件描述符并处理该通道上的读事件。
  }
  ::close(fd_);  //关闭epoll文件描述符
}

void PollerEpoll::addChannel(Channel* ch) {
  struct epoll_event ev;
  memset(&ev, 0, sizeof(ev));
  ev.events = ch->events();
  ev.data.ptr = ch;
  int r = epoll_ctl(fd_, EPOLL_CTL_ADD, ch->fd(), &ev); //将通道内的文件描述符和其关心的事件添加到epoll监听中。
　liveChannels_.insert(ch);
}

void PollerEpoll::updateChannel(Channel* ch) {
  struct epoll_event ev;
  memset(&ev, 0, sizeof(ev));
  ev.events = ch->events();
  ev.data.ptr = ch;
  int r = epoll_ctl(fd_, EPOLL_CTL_MOD, ch->fd(), &ev);
}

void PollerEpoll::removeChannel(Channel* ch) {
  liveChannels_.erase(ch);
  for (int i = lastActive_; i >= 0; i--) {
    if (ch == activeEvs_[i].data.ptr) {
      activeEvs_[i].data.ptr = NULL;
      break;
    }
  }
}

//核心函数
void PollerEpoll::loop_once(int waitMs) {
  lastActive_ = epoll_wait(fd_, activeEvs_, kMaxEvents, waitMs);
  while (--lastActive_ >= 0) {
    int i = lastActive_;
    Channel* ch = (Channel*)activeEvs_[i].data.ptr;
    int events = activeEvs_[i].events;
    if (ch) {
      if (events & kWriteEvent) {
        ch->handleWrite();
      }
      if (events & (kReadEvent | POLLERR)) {
        ch->handleRead();
      }
      if (!(events & (kReadEvent | kWriteEvent | POLLERR))) {
        fatal("unexpected poller events");
      }
    }
  }
}