网络编程入门04
Poll函数
#include <poll.h>
int poll(struct pollfd fd[], nfds_t nfds, int timeout);
参数：
1）第一个参数:一个结构数组,struct pollfd结构如下：
struct pollfd{
int fd; //文件描述符
short events; //请求的事件
short revents; //返回的事件
};
2）第二个参数nfds：要监视的描述符的数目。
3）最后一个参数timeout：是一个用毫秒表示的时间，是指定poll在返回前没有接收事件时应该等待的时间。如果 它的值为-1，poll就永远都不会超时。如果整数值为32个比特，那么最大的超时周期大约是30分钟。
poll函数的事件标志符值
常量 说明
POLLIN 普通或优先级带数据可读
POLLRDNORM 普通数据可读
POLLRDBAND 优先级带数据可读
POLLPRI 高优先级数据可读
POLLOUT 普通数据可写
POLLWRNORM 普通数据优先级数据可写
POLLWRBAND 优先级带数据可写
POLLERR 发生错误
POLLHUP 发生挂起
POLLNVAL 描述字不是一个打开的文件
fd_set 与 select 关系先要了解.
int select(int nfds, fd_set *readfds, fd_set *writefds,fd_set *exceptfds, struct timeval *timeout);
参数说明：
nfds：监听的所有文件描述符中的最大描述符+1（其实内核是轮询查的）
readfds：读文件描述符监听集合
writefds：写文件描述符监听集合
exceptfds：异常文件描述符监听集合
timeout：有几个值如下：
大于0：设置监听超时时长
NULL：阻塞监听
0：非阻塞监听
函数返回值：
大于0：所有监听集合（3个）中，满足对应事件的总数
0：没有满足的
-1：出错error
void FD_CLR(int fd, fd_set *set); //将一个文件描述符从集合中移除
int FD_ISSET(int fd, fd_set *set); //判断一个文件描述符是否在一个集合中，返回值：在 1，不在 0
void FD_SET(int fd, fd_set *set); //将监听的文件描述符，添加到监听集合中
void FD_ZERO(fd_set *set); //清空一个文件描述符集合
time_val{
long tv_sec; //seconds
long tv_usec;// microseconds
}
Channel.h
calss Channel{
public:
typedef std::function<void()> EventCallback; //无参数可调用对象 为事件回调
typedef std::function<void(Timestamp)> ReadEventCallback; //带有时间戳参数的为 读事件回调
private:
static const int kNoneEvent = 0 //先定义三个事件常量
static const int kReadEvent = POLLIN | POLLPRI;
static const int kWriteEvent = POLLOUT;
EventLoop* loop_; //主循环
const int fd_; //监控的文件描述符
int events_; //监控的事件
int revents_; // it's the received event types of epoll or poll //收到的事件
int index_; // used by Poller.
bool logHup_;
std::weak_ptr<void> tie_;
bool tied_;
bool eventHandling_;
bool addedToLoop_;
ReadEventCallback readCallback_;
EventCallback writeCallback_;
EventCallback closeCallback_;
EventCallback errorCallback_;
public:
ctr(EventLoop* loop, int fd) //构造函数
: loop_(loop),
fd_(fd__),
events_(0),
revents_(0),
index_(-1), //出事index为-1 对应的channel在 轮训器中pollfd数组中下标的位置
logHup_(true),
tied_(false),
eventHandling_(false),
addedToLoop_(false)
{ }
~dtr(){ //析构函数
assert(!eventHandling_); //确定当前未处理时间
assert(!addedToLoop_); //确定没有加入到某个事件循环
if(loop_->isInLoopThread()) //如果当前线程为循环所在线程
{
assert(!loop_->hasChannel(this)); //确定这个时间没有这个频道
}
}
void handleEvent(Timestamp receiveTime){
std::shared_ptr<void> guard;
if (tied_) //如果有一个弱指针指向了一个类外对象
{
guard = tie_.lock(); //将指针提升为引用计数指针，保证在处理事件中，tie_指向的内存不会被析构
if (guard)
{
handleEventWithGuard(receiveTime);
}
}
else
{
handleEventWithGuard(receiveTime);
}
}
//设定几个事件的回调函数
void setReadCallback(ReadEventCallback cb)
void tie(const std::shared_ptr<void>& obj) {
tie_ = obj; //防止obj被析构，用一个弱指针指针帮助不会被析构
tied_ = true;
}
int fd() const { return fd_; }
int events() const { return events_; }
void set_revents(int revt) { revents_ = revt; } // used by pollers
// int revents() const { return revents_; }
bool isNoneEvent() const { return events_ == kNoneEvent; }
void enableReading() { events_ |= kReadEvent; update(); }
void disableReading() { events_ &= ~kReadEvent; update(); }
void enableWriting() { events_ |= kWriteEvent; update(); }
void disableWriting() { events_ &= ~kWriteEvent; update(); }
void disableAll() { events_ = kNoneEvent; update(); }
bool isWriting() const { return events_ & kWriteEvent; }
bool isReading() const { return events_ & kReadEvent; }
// for Poller
int index() { return index_; }
void set_index(int idx) { index_ = idx; }
// for debug
string reventsToString() const {
//调用 eventsToString(int fd, int ev);
}
string eventsToString() const {
//调用 eventsToString(int fd, int ev);
}
void doNotLogHup() { logHup_ = false; }
EventLoop* ownerLoop() { return loop_; }
void remove() { //频道对象移除循环对象
addedToLoop_ = false;
loop_->removeChannel(this);
}
private:
static string eventsToString(int fd, int ev) {
//把一些信息以字符串返回
}
void update() { //把频道对象加入循环对象
addedToLoop_ = true;
loop_->updateChannel(this);
}
void handleEventWithGuard(Timestamp receiveTime) {
//有什么样的事件，调用什么样的处理回调处理
}
}
Poller.h 轮训器基类
class Poller{
protected: //子类可继承
typedef std::map<int, Channel*> ChannelMap;
ChannelMap channels_; //有一个int到频道指针的映射 文件描述符到频道指针映射
private:
EventLoop* ownerLoop_; //有一个事件循环对象
public:
typedef std::vector<Channel*> ChannelList;
Poller(EventLoop* loop); //直接赋值loop的构造器
virtual ~Poller(); //默认析构器
virtual Timestamp poll(int timeoutMs, ChannelList* activeChannels) = 0; //给一个时间，限制和频道指针列表
virtual void updateChannel(Channel* channel) = 0; //更新频道
virtual void removeChannel(Channel* channel) = 0;//去除频道
virtual bool hasChannel(Channel* channel) const; //判断这个轮训器是否有这个频道
{
assertInLoopThread();
ChannelMap::const_iterator it = channels_.find(channel->fd()); //根据频道描述符查找
return it != channels_.end() && it->second == channel;
}
static Poller* newDefaultPoller(EventLoop* loop);//给一个循环对象指针，返回一个一个默认轮训器
void assertInLoopThread() const;//判断当前线程是否持有一个事件循环对象
}
PollPoller.h Poll轮询器
class PollPoller : Poller {
private:
typedef std::vector<struct pollfd> PollFdList;
PollFdList pollfds_;
void fillActiveChannels(int numEvents,
ChannelList* activeChannels) const {
for (PollFdList::const_iterator pfd = pollfds_.begin();
pfd != pollfds_.end() && numEvents > 0; ++pfd) //遍历这颗红黑树
{
if (pfd->revents > 0) //如果这个pollfd --文件描述符对应的文件有任务就绪
{
--numEvents;
ChannelMap::const_iterator ch = channels_.find(pfd->fd); //根据文件描述符找到对于的频道指针
assert(ch != channels_.end());
Channel* channel = ch->second;
assert(channel->fd() == pfd->fd);
channel->set_revents(pfd->revents); //这个频道把返回事件设定
// pfd->revents = 0;
activeChannels->push_back(channel); //加入活跃列表
}
}
}
public:
PollPoller(EventLoop* loop) { //直接把指针给父类 简单构造
}
~PollPoller() override; //默认析构
Timestamp poll(int timeoutMs, ChannelList* activeChannels) override {
int numEvents = ::poll(&*pollfds_.begin(), pollfds_.size(), timeoutMs); //轮询 poll在有事件返回或者超时前会阻塞
int savedErrno = errno;
Timestamp now(Timestamp::now());
if (numEvents > 0) //如果有任务
{
LOG_TRACE << numEvents << " events happened";
fillActiveChannels(numEvents, activeChannels); //如果有任务，就把这些时间加入活跃频道列表
}
else if (numEvents == 0) //如果没有事件就绪
{
LOG_TRACE << " nothing happened";
}
else //出错
{
if (savedErrno != EINTR)
{
errno = savedErrno;
LOG_SYSERR << "PollPoller::poll()";
}
}
return now;
}
void updateChannel(Channel* channel) override {
Poller::assertInLoopThread();
if (channel->index() < 0) //这个频道的index为-1，说明没被加入任何轮训器中
{
// a new one, add to pollfds_
assert(channels_.find(channel->fd()) == channels_.end());
struct pollfd pfd;
pfd.fd = channel->fd();
pfd.events = static_cast<short>(channel->events());
pfd.revents = 0;
pollfds_.push_back(pfd);
int idx = static_cast<int>(pollfds_.size())-1;
channel->set_index(idx); //这个频道的index设为轮训器中poolfd数组下标位置
channels_[pfd.fd] = channel;
}
else //这个频道已经被加入过轮训器中
{
// update existing one
assert(channels_.find(channel->fd()) != channels_.end()); //确定这个频道是加入由这个轮训器监控
assert(channels_[channel->fd()] == channel);
int idx = channel->index();
assert(0 <= idx && idx < static_cast<int>(pollfds_.size()));
struct pollfd& pfd = pollfds_[idx];
assert(pfd.fd == channel->fd() || pfd.fd == -channel->fd()-1); //负数是让轮训器不关注这个时间
pfd.fd = channel->fd();
pfd.events = static_cast<short>(channel->events());
pfd.revents = 0;
if (channel->isNoneEvent())
{
// ignore this pollfd
pfd.fd = -channel->fd()-1;
}
}
}
void removeChannel(Channel* channel) override {
Poller::assertInLoopThread();
LOG_TRACE << "fd = " << channel->fd();
assert(channels_.find(channel->fd()) != channels_.end());
assert(channels_[channel->fd()] == channel);
assert(channel->isNoneEvent());
int idx = channel->index();
assert(0 <= idx && idx < static_cast<int>(pollfds_.size()));
const struct pollfd& pfd = pollfds_[idx]; (void)pfd;
assert(pfd.fd == -channel->fd()-1 && pfd.events == channel->events()); //要确认这个时间已经不被关注了
size_t n = channels_.erase(channel->fd());
assert(n == 1); (void)n;
if (implicit_cast<size_t>(idx) == pollfds_.size()-1)
{
pollfds_.pop_back();
}
else //不需要移动整个数组，只需要和最后一个换一下然后pop_back
{
int channelAtEnd = pollfds_.back().fd;
iter_swap(pollfds_.begin()+idx, pollfds_.end()-1);
if (channelAtEnd < 0)
{
channelAtEnd = -channelAtEnd-1;
}
channels_[channelAtEnd]->set_index(idx);
pollfds_.pop_back();
}
}
}
EPollPoller.h 整体结构和PollPoller很类似
epoll_event结构体一般用在epoll机制中，其定义如下：
struct epoll_event
{
uint32_t events; /* Epoll events */
epoll_data_t data; /* User data variable */
} __attribute__ ((__packed__));
typedef union epoll_data
{
void *ptr;
int fd;
uint32_t u32;
uint64_t u64;
} epoll_data_t;
*const int kNew = -1; *
*const int kAdded = 1;*
*const int kDeleted = 2;*
class EPollPoller : public Poller
{
private:
typedef std::vector<struct epoll_event> EventList;
int epollfd_;
EventList events_; //epoll_event数组
public:
/*
int epoll_create1(int flags);
功能：创建一个多路复用的实例
参数：
flags：
0:如果这个参数是0，这个函数等价于poll_create（0）
EPOLL_CLOEXEC：这是这个参数唯一的有效值，如果这个参数设置为这个。那么当进程替换映像的时候会关闭这个文件描述符，这样新的映像中就无法对这个文件描述符操作，适用于多进程编程+映像替换的环境里
返回值：
success：返回一个非0 的未使用过的最小的文件描述符
error：-1 errno被设置
*/
EPollPoller(EventLoop* loop)
: Poller(loop),
epollfd_(::epoll_create1(EPOLL_CLOEXEC)),
events_(kInitEventListSize) // 16
{
if (epollfd_ < 0)
{
LOG_SYSFATAL << "EPollPoller::EPollPoller";
}
}
~EPollPoller() override {
::close(epollfd_);
}
/*
int epoll_wait(int epfd, struct epoll_event *events,int maxevents, int timeout);
功能：等待一个epoll队列中的文件描述符的I/O事件发生
参数：
epfd：目标epoll队列的描述符
events：用于放置epoll队列中准备就绪（被触发）的事件
maxevents：最大事件？
timeout：指定函数等待的时间。这个函数阻塞这么长一段时间之后接触阻塞。
返回值：
>=0，表示准备就绪的文件描述符个数
-1：出错，errno被设置
*/
Timestamp poll(int timeoutMs, ChannelList* activeChannels) override {
int numEvents = ::epoll_wait(epollfd_,
&*events_.begin(),
static_cast<int>(events_.size()),
timeoutMs);
int savedErrno = errno;
Timestamp now(Timestamp::now());
if (numEvents > 0)
{
LOG_TRACE << numEvents << " events happened";
fillActiveChannels(numEvents, activeChannels); //加入活跃频道
if (implicit_cast<size_t>(numEvents) == events_.size())
{
events_.resize(events_.size()*2);
}
}
else if (numEvents == 0)
{
LOG_TRACE << "nothing happened";
}
else
{
// error happens, log uncommon ones
if (savedErrno != EINTR)
{
errno = savedErrno;
LOG_SYSERR << "EPollPoller::poll()";
}
}
return now;
}
/*
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
RETURN：0，成功；-1，出错
函数描述：
(1) epfd为epoll_create创建的epoll描述符
(2) epoll_ctl函数对epoll进行op类型的操作，op选项为
EPOLL_CTL_ADD，对fd描述符注册event事件
EPOLL_CTL_MOD，对fd描述符的event事件进行修改
EPOLL_CTL_DEL，删除已注册的event事件
*/
void updateChannel(Channel* channel) override {
Poller::assertInLoopThread();
const int index = channel->index();
LOG_TRACE << "fd = " << channel->fd() << " events = " << channel->events() << " index = " << index;
if (index == kNew || index == kDeleted) //如果这个channel 索引为新，活着被删除
{
// a new one, add with EPOLL_CTL_ADD
int fd = channel->fd();
if (index == kNew)
{
assert(channels_.find(fd) == channels_.end());
channels_[fd] = channel; //加入文件映射中
}
else // index == kDeleted //这里的删除可以理解为不关注这个事件
{
assert(channels_.find(fd) != channels_.end());
assert(channels_[fd] == channel);
}
channel->set_index(kAdded); //设置为关注
update(EPOLL_CTL_ADD, channel);
}
else
{
// update existing one with EPOLL_CTL_MOD/DEL //这个文件描述符已经被关注
int fd = channel->fd();
(void)fd;
assert(channels_.find(fd) != channels_.end());
assert(channels_[fd] == channel);
assert(index == kAdded);
if (channel->isNoneEvent()) //如果这个频道没事，就把他关注
{
update(EPOLL_CTL_DEL, channel);
channel->set_index(kDeleted); //设置为被取消关注
}
else
{
update(EPOLL_CTL_MOD, channel);
}
}
}
void removeChannel(Channel* channel) override {
Poller::assertInLoopThread();
int fd = channel->fd();
LOG_TRACE << "fd = " << fd;
assert(channels_.find(fd) != channels_.end());
assert(channels_[fd] == channel);
assert(channel->isNoneEvent());
int index = channel->index();
assert(index == kAdded || index == kDeleted);
size_t n = channels_.erase(fd); //在事件映射出，删除这个fd 代表轮训器不处理这个频道了
(void)n;
assert(n == 1);
if (index == kAdded)
{
update(EPOLL_CTL_DEL, channel);
}
channel->set_index(kNew);
}
private:
static const int kInitEventListSize = 16;
static const char* operationToString(int op);
void fillActiveChannels(int numEvents,
ChannelList* activeChannels) const {
for (int i = 0; i < numEvents; ++i) //event_里返回的都是已经就绪的
{
Channel* channel = static_cast<Channel*>(events_[i].data.ptr);
#ifndef NDEBUG
int fd = channel->fd();
ChannelMap::const_iterator it = channels_.find(fd);
assert(it != channels_.end());
assert(it->second == channel);
#endif
channel->set_revents(events_[i].events);
activeChannels->push_back(channel);
}
}
void update(int operation, Channel* channel) { //对这个频道的事件进行注册或者修改管理
struct epoll_event event;
memZero(&event, sizeof event);
event.events = channel->events();
event.data.ptr = channel;
int fd = channel->fd();
LOG_TRACE << "epoll_ctl op = " << operationToString(operation) << " fd = " << fd << " event = { " << channel->eventsToString() << " }";
if (::epoll_ctl(epollfd_, operation, fd, &event) < 0)
{
if (operation == EPOLL_CTL_DEL)
{
LOG_SYSERR << "epoll_ctl op =" << operationToString(operation) << " fd =" << fd;
}
else
{
LOG_SYSFATAL << "epoll_ctl op =" << operationToString(operation) << " fd =" << fd;
}
}
}
typedef std::vector<struct epoll_event> EventList;
int epollfd_;
EventList events_;
};
