I/O多路转接之poll

多路转接之poll"/>

I/O多路转接之poll

承接上文：I/O多路转接之select-CSDN博客

简介

poll原型介绍

select代码改造成poll型

poll优缺点

在前文中我们得知了，select的诸多缺点，接下来这个poll就可以解决上述出现的问题

poll也是一种Linux中的多路转接的方案，主要解决下面这两个问题

1. select的fd有上限的问题

2. 每次调用都要重新设置关心的fd

poll原型介绍

events和revents的取值

 纯大写，全是系统内定义出来的宏

其中比较重要并且常用的就那么几个，比如POLLIN(读)，POLLOUT(写)，POLLERR(错误),还有一个POLLPRI(就是TCP中的那个带外数据)

代码改造

poll在实际上其实在代码书写上是比select要简单的，只要稍加改造就可以了

err.hpp

#pragma once#include <iostream>enum
{USAGE_ERR = 1,SOCKET_ERR,BIND_ERR,LISTEN_ERR
};

log.hpp

#pragma once#include <iostream>
#include <string>
#include <cstdarg>
#include <ctime>
#include <unistd.h>#define DEBUG   0
#define NORMAL  1
#define WARNING 2
#define ERROR   3
#define FATAL   4const char * to_levelstr(int level)
{switch(level){case DEBUG : return "DEBUG";case NORMAL: return "NORMAL";case WARNING: return "WARNING";case ERROR: return "ERROR";case FATAL: return "FATAL";default : return nullptr;}
}void logMessage(int level, const char *format, ...)
{
#define NUM 1024char logprefix[NUM];snprintf(logprefix, sizeof(logprefix), "[%s][%ld][pid: %d]",to_levelstr(level), (long int)time(nullptr), getpid());char logcontent[NUM];va_list arg;va_start(arg, format);vsnprintf(logcontent, sizeof(logcontent), format, arg);std::cout << logprefix << logcontent << std::endl;
}

main

#include "pollServer.hpp"
#include "err.hpp"
#include <memory>using namespace std;
using namespace poll_ns;static void usage(std::string proc)
{std::cerr << "Usage:\n\t" << proc << " port" << "\n\n";
}std::string transaction(const std::string &request)
{return request;
}// ./select_server 8081
int main(int argc, char *argv[])
{// if(argc != 2)// {//     usage(argv[0]);//     exit(USAGE_ERR);// }// unique_ptr<SelectServer> svr(new SelectServer(atoi(argv[1])));// std::cout << "test: " << sizeof(fd_set) * 8 << std::endl;unique_ptr<PollServer> svr(new PollServer(transaction));svr->initServer();svr->start();return 0;
}

makefile

poll_server: maing++ -o $@ $^ -std=c++11
.PHONY:clean
clean:rm -f poll_server

pollServer.hpp

#pragma once#include <iostream>
#include <string>
#include <functional>
#include <poll.h>
#include "sock.hpp"namespace poll_ns
{static const int defaultport = 8081;static const int num = 2048;static const int defaultfd = -1;using func_t = std::function<std::string (const std::string&)>;class PollServer{public:PollServer(func_t f, int port = defaultport) : _func(f), _port(port), _listensock(-1), _rfds(nullptr){}void initServer(){_listensock = Sock::Socket();Sock::Bind(_listensock, _port);Sock::Listen(_listensock);_rfds = new struct pollfd[num];for (int i = 0; i < num; i++) ResetItem(i);_rfds[0].fd = _listensock; // 不变了_rfds[0].events = POLLIN;}void Print(){std::cout << "fd list: ";for (int i = 0; i < num; i++){if (_rfds[i].fd != defaultfd)std::cout << _rfds[i].fd << " ";}std::cout << std::endl;}void ResetItem(int i){_rfds[i].fd = defaultfd;_rfds[i].events = 0;_rfds[i].revents = 0;}void Accepter(int listensock){logMessage(DEBUG, "Accepter in");// 走到这里，accept 函数，会不会阻塞？？？1 0// select 告诉我， listensock读事件就绪了std::string clientip;uint16_t clientport = 0;int sock = Sock::Accept(listensock, &clientip, &clientport); // accept = 等 + 获取if (sock < 0)return;logMessage(NORMAL, "accept success [%s:%d]", clientip.c_str(), clientport);// sock我们能直接recv/read 吗？不能，整个代码，只有select有资格检测事件是否就绪// 将新的sock 托管给select！// 将新的sock托管给select的本质，其实就是将sock，添加到fdarray数组中即可！int i = 0;for (; i < num; i++){if (_rfds[i].fd != defaultfd)continue;elsebreak;}if (i == num){logMessage(WARNING, "server if full, please wait");close(sock);}else{_rfds[i].fd = sock;_rfds[i].events = POLLIN;_rfds[i].revents = 0;}Print();logMessage(DEBUG, "Accepter out");}void Recver(int pos){logMessage(DEBUG, "in Recver");// 1. 读取request// 这样读取是有问题的！char buffer[1024];ssize_t s = recv(_rfds[pos].fd, buffer, sizeof(buffer) - 1, 0); // 这里在进行读取的时候，会不会被阻塞？1， 0if (s > 0){buffer[s] = 0;logMessage(NORMAL, "client# %s", buffer);}else if (s == 0){close(_rfds[pos].fd);ResetItem(pos);logMessage(NORMAL, "client quit");return;}else{close(_rfds[pos].fd);ResetItem(pos);logMessage(ERROR, "client quit: %s", strerror(errno));return;}// 2. 处理requeststd::string response = _func(buffer);// 3. 返回response// write bugwrite(_rfds[pos].fd, response.c_str(), response.size());logMessage(DEBUG, "out Recver");}// 1. handler event rfds 中，不仅仅是有一个fd是就绪的，可能存在多个// 2. 我们的select目前只处理了read事件void HandlerReadEvent(){for (int i = 0; i < num; i++){// 过滤掉非法的fdif (_rfds[i].fd == defaultfd)continue;if (!(_rfds[i].events & POLLIN)) continue;// 正常的fd// 正常的fd不一定就绪了// 目前一定是listensock，只有这一个if (_rfds[i].fd== _listensock && (_rfds[i].revents & POLLIN))Accepter(_listensock);else if(_rfds[i].revents & POLLIN)Recver(i);else{}}}void start(){int timeout = 1000;for (;;){int n = poll(_rfds, num, timeout);switch (n){case 0:logMessage(NORMAL, "timeout...");break;case -1:logMessage(WARNING, "poll error, code: %d, err string: %s", errno, strerror(errno));break;default:// 说明有事件就绪了,目前只有一个监听事件就绪了logMessage(NORMAL, "have event ready!");HandlerReadEvent();// HandlerWriteEvent(wfds);break;}}}~PollServer(){if (_listensock < 0)close(_listensock);if (_rfds)delete[] _rfds;}private:int _port;int _listensock;struct pollfd *_rfds;func_t _func;};
}

sock.hpp

#pragma once#include <iostream>
#include <string>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "log.hpp"
#include "err.hpp"class Sock
{const static int backlog = 32;public:static int Socket(){// 1. 创建socket文件套接字对象int sock = socket(AF_INET, SOCK_STREAM, 0);if (sock < 0){logMessage(FATAL, "create socket error");exit(SOCKET_ERR);}logMessage(NORMAL, "create socket success: %d", sock);int opt = 1;setsockopt(sock, SOL_SOCKET, SO_REUSEADDR|SO_REUSEPORT, &opt, sizeof(opt));return sock;}static void Bind(int sock, int port){// 2. bind绑定自己的网络信息struct sockaddr_in local;memset(&local, 0, sizeof(local));local.sin_family = AF_INET;local.sin_port = htons(port);local.sin_addr.s_addr = INADDR_ANY;if (bind(sock, (struct sockaddr *)&local, sizeof(local)) < 0){logMessage(FATAL, "bind socket error");exit(BIND_ERR);}logMessage(NORMAL, "bind socket success");}static void Listen(int sock){// 3. 设置socket 为监听状态if (listen(sock, backlog) < 0) // 第二个参数backlog后面在填这个坑{logMessage(FATAL, "listen socket error");exit(LISTEN_ERR);}logMessage(NORMAL, "listen socket success");}static int Accept(int listensock, std::string *clientip, uint16_t *clientport){struct sockaddr_in peer;socklen_t len = sizeof(peer);int sock = accept(listensock, (struct sockaddr *)&peer, &len);if (sock < 0)logMessage(ERROR, "accept error, next");else{logMessage(NORMAL, "accept a new link success, get new sock: %d", sock); // ?*clientip = inet_ntoa(peer.sin_addr);*clientport = ntohs(peer.sin_port);}return sock;}
};

测试结果

Poll的特点

优点

不同与select使用三个位图来表示三个fdset的方式， poll使用一个pollfd的指针实现
 

        pollfd结构包含了要监视的event和发生的event，不再使用select“参数-值”传递的方式. 接口使用比select更方便；

        poll并没有最大数量限制 (但是数量过大后性能也是会下降)；

 缺点

poll中监听的文件描述符数目增多时，因为它是以线性遍历的方式进行查看，所以我们就有了下一个接口epoll，这个接口才是集百家之长处
 

        和select函数一样， poll返回后，需要轮询pollfd来获取就绪的描述符；
        每次调用poll都需要把大量的pollfd结构从用户态拷贝到内核中；
        同时连接的大量客户端在一时刻可能只有很少的处于就绪状态, 因此随着监视的描述符数量的增长, 其效率也会线性下降；