muduo源码剖析之poller/EpollPoller多路复用类

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muduo源码剖析之poller/EpollPoller多路复用类

简介

poller是I/O多路复用接口抽象虚基类,对I/O多路复用API的封装,muduo提供了EPollPoller和PollPoller派生类(epoll和poll),所以不支持select.

newDefaultPoller()默认选择epoll

主要接口

poll

是Poller的核心功能，使用派生类的poll或者epoll_wait来阻塞等待IO事件发生
通过派生类的实现来填充EventLoop的activeChannelList_

static createNewPoller：

工厂函数，创建一个Poller实例
在EpollPoller中，每个实例对应一个epollfd

update

更新I/O多路复用的状态，例如epoll_ctl的ADD，MOD，DEL

主要成员

loop

控制当前Poller的EventLoop指针
其余成员由派生类实现

源码剖析

poller.h

#ifndef MUDUO_NET_POLLER_H
#define MUDUO_NET_POLLER_H#include <map>
#include <vector>#include "muduo/base/Timestamp.h"
#include "muduo/net/EventLoop.h"namespace muduo
{
namespace net
{class Channel;///
/// Base class for IO Multiplexing
///
/// This class doesn't own the Channel objects.
class Poller : noncopyable
{public:typedef std::vector<Channel*> ChannelList;Poller(EventLoop* loop);virtual ~Poller();/// Polls the I/O events./// Must be called in the loop thread.virtual Timestamp poll(int timeoutMs, ChannelList* activeChannels) = 0;/// Changes the interested I/O events./// Must be called in the loop thread.virtual void updateChannel(Channel* channel) = 0;/// Remove the channel, when it destructs./// Must be called in the loop thread.virtual void removeChannel(Channel* channel) = 0;//判断是否存在virtual bool hasChannel(Channel* channel) const;//创建一个poller,默认是epollstatic Poller* newDefaultPoller(EventLoop* loop);void assertInLoopThread() const{ownerLoop_->assertInLoopThread();}protected:typedef std::map<int, Channel*> ChannelMap;ChannelMap channels_;private:EventLoop* ownerLoop_;
};}  // namespace net
}  // namespace muduo#endif  // MUDUO_NET_POLLER_H

poller

#include "muduo/net/Poller.h"
#include "muduo/net/Channel.h"using namespace muduo;
using namespace muduo::net;Poller::Poller(EventLoop* loop): ownerLoop_(loop)
{
}Poller::~Poller() = default;bool Poller::hasChannel(Channel* channel) const
{assertInLoopThread();ChannelMap::const_iterator it = channels_.find(channel->fd());return it != channels_.end() && it->second == channel;
}

EPollPoller.h

#ifndef MUDUO_NET_POLLER_EPOLLPOLLER_H
#define MUDUO_NET_POLLER_EPOLLPOLLER_H#include "muduo/net/Poller.h"#include <vector>struct epoll_event;namespace muduo
{
namespace net
{///
/// IO Multiplexing with epoll(4).
///
class EPollPoller : public Poller
{public:EPollPoller(EventLoop* loop);~EPollPoller() override;Timestamp poll(int timeoutMs, ChannelList* activeChannels) override;void updateChannel(Channel* channel) override;void removeChannel(Channel* channel) override;private:static const int kInitEventListSize = 16;static const char* operationToString(int op);void fillActiveChannels(int numEvents,ChannelList* activeChannels) const;void update(int operation, Channel* channel);typedef std::vector<struct epoll_event> EventList;int epollfd_;EventList events_;
};}  // namespace net
}  // namespace muduo
#endif  // MUDUO_NET_POLLER_EPOLLPOLLER_H

EPollPoller

// Copyright 2010, Shuo Chen.  All rights reserved.
// /
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.// Author: Shuo Chen (chenshuo at chenshuo dot com)#include "muduo/net/poller/EPollPoller.h"#include "muduo/base/Logging.h"
#include "muduo/net/Channel.h"#include <assert.h>
#include <errno.h>
#include <poll.h>
#include <sys/epoll.h>
#include <unistd.h>using namespace muduo;
using namespace muduo::net;/*struct epoll_event
{uint32_t events;   //Epoll eventsepoll_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;*/// On Linux, the constants of poll(2) and epoll(4)
// are expected to be the same.
static_assert(EPOLLIN == POLLIN,        "epoll uses same flag values as poll");
static_assert(EPOLLPRI == POLLPRI,      "epoll uses same flag values as poll");
static_assert(EPOLLOUT == POLLOUT,      "epoll uses same flag values as poll");
static_assert(EPOLLRDHUP == POLLRDHUP,  "epoll uses same flag values as poll");
static_assert(EPOLLERR == POLLERR,      "epoll uses same flag values as poll");
static_assert(EPOLLHUP == POLLHUP,      "epoll uses same flag values as poll");namespace
{
const int kNew = -1; //channel尚未添加到poller中
const int kAdded = 1; //已经添加了
const int kDeleted = 2;   //之前监听过了，后来移除了监听
}//当flag = EPOLL_CLOEXEC，创建的epfd会设置FD_CLOEXEC
//FD_CLOEXEC表示当程序执行exec函数时本fd将被系统自动关闭,表示不传递给exec创建的新进程
EPollPoller::EPollPoller(EventLoop* loop): Poller(loop),//创建epollfd，使用带1的版本//如果参数为0,则与epoll_create版本相同,设置为O_CLOEXEC,查看open函数的这个参数解释,//子进程fork并调用exec时会关闭这个fdepollfd_(::epoll_create1(EPOLL_CLOEXEC)),      events_(kInitEventListSize)                    //vector这样用时初始化kInitEventListSize个大小空间,默认16
{if (epollfd_ < 0)                           //在构造函数中判断，<0就abort(){LOG_SYSFATAL << "EPollPoller::EPollPoller";}
}EPollPoller::~EPollPoller()
{::close(epollfd_);
}Timestamp EPollPoller::poll(int timeoutMs, ChannelList* activeChannels)//ChannelList是一个存放channel的vector
{LOG_TRACE << "fd total count " << channels_.size();int numEvents = ::epoll_wait(epollfd_,&*events_.begin(),  //events_已初始化,是存放epoll_event的vectorstatic_cast<int>(events_.size()),    //监控套接字的数目timeoutMs);int savedErrno = errno;Timestamp now(Timestamp::now());if (numEvents > 0){LOG_TRACE << numEvents << " events happened";fillActiveChannels(numEvents, activeChannels);if (implicit_cast<size_t>(numEvents) == events_.size()) //如果返回的事件数目等于当前事件数组大小，就分配2倍空间{events_.resize(events_.size()*2);}}else if (numEvents == 0){LOG_TRACE << "nothing happened";}else{// error happens, log uncommon onesif (savedErrno != EINTR){errno = savedErrno;LOG_SYSERR << "EPollPoller::poll()";}}return now;
}//把返回到的这么多个事件添加到activeChannels
void EPollPoller::fillActiveChannels(int numEvents,ChannelList* activeChannels) const   
{assert(implicit_cast<size_t>(numEvents) <= events_.size());for (int i = 0; i < numEvents; ++i)                          //确定它的大小小于events_的大小，因为events_是预留的事件vector{Channel* channel = static_cast<Channel*>(events_[i].data.ptr);
#ifndef NDEBUGint fd = channel->fd();                       //debug时做一下检测ChannelMap::const_iterator it = channels_.find(fd);assert(it != channels_.end());assert(it->second == channel);
#endifchannel->set_revents(events_[i].events);        //把已发生的事件传给channel,写到通道当中activeChannels->push_back(channel);             //并且push_back进activeChannels}
}//这个函数被调用是因为channel->enablereading()被调用，再调用channel->update()，再event_loop->updateChannel()，再->epoll或poll的updateChannel被调用
//
void EPollPoller::updateChannel(Channel* channel)
{Poller::assertInLoopThread();  //在IO线程const int index = channel->index();  //初始状态index是-1LOG_INFO << "fd = " << channel->fd()<< " events = " << channel->events() << " index = " << index;// 当是新的或是之前监听过，后来移除了监听// 两者的区别在于,新的channel 之前没有在epoll 中保存// 而 del 的之前在 channels_ 中保存了，但是没有被放入epoll_ctl中监听if (index == kNew || index == kDeleted)  //index是在poll中是下标，在epoll中是三种状态，上面有三个常量{// a new one, add with EPOLL_CTL_ADDint fd = channel->fd();if (index == kNew){assert(channels_.find(fd) == channels_.end());  //channels_是一个Mapchannels_[fd] = channel;}else // index == kDeleted{assert(channels_.find(fd) != channels_.end());assert(channels_[fd] == channel);}channel->set_index(kAdded);update(EPOLL_CTL_ADD, channel);   //注册事件}else{// update existing one with EPOLL_CTL_MOD/DELint fd = channel->fd();(void)fd;assert(channels_.find(fd) != channels_.end());assert(channels_[fd] == channel);assert(index == kAdded);// 既然已经添加了，那么可能的修改就是修改监听的时间，或者不在监听// 因此这里先判断是否是没有监听的事件了，如果是那么直接移除、if (channel->isNoneEvent())   //判断无事件{update(EPOLL_CTL_DEL, channel);    //删除事件channel->set_index(kDeleted);  //删除后被设置为kDeleted}else{update(EPOLL_CTL_MOD, channel);   //修改已注册的监听事件}}
}void EPollPoller::removeChannel(Channel* channel)
{Poller::assertInLoopThread();  //判断是否在IO线程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);   //删除(void)n; assert(n == 1);if (index == kAdded){update(EPOLL_CTL_DEL, channel);}channel->set_index(kNew);
}void EPollPoller::update(int operation, Channel* channel)
{printf("-------%s,line.%d-------\n",__FUNCTION__,__LINE__);struct epoll_event event;    //存放数据的结构体memZero(&event, sizeof event);event.events = channel->events();  //注册的事件event.data.ptr = channel;int fd = channel->fd();LOG_INFO << "epoll_ctl op = " << operationToString(operation)<< " fd = " << fd << " event = { " << channel->eventsToString() << " }";if (::epoll_ctl(epollfd_, operation, fd, &event) < 0)//epoll_ctl失败返回-1{if (operation == EPOLL_CTL_DEL){LOG_SYSERR << "epoll_ctl op =" << operationToString(operation) << " fd =" << fd;}else{LOG_SYSFATAL << "epoll_ctl op =" << operationToString(operation) << " fd =" << fd;}}
}const char* EPollPoller::operationToString(int op)
{switch (op){case EPOLL_CTL_ADD:return "ADD";case EPOLL_CTL_DEL:return "DEL";case EPOLL_CTL_MOD:return "MOD";default:assert(false && "ERROR op");return "Unknown Operation";}
}