一、IO多路转接之poll
1.1poll函数接口
1.2poll函数返回值
1.3poll参数
二、poll服务器代码
2.1PollServer.hpp文件
#pragma once #include <iostream> #include <sys/select.h> #include <sys/time.h> #include <poll.h> #include "Sock.hpp" static const uint16_t defaultport = 8080; static const int fd_num_max = 64; int defaultfd = -1; int non_event = 0; class PollServer { public: PollServer(uint16_t port = defaultport) : _port(port) { for (size_t i = 0; i < fd_num_max; i++) { _event_fds[i].fd = defaultfd; _event_fds[i].events = non_event; _event_fds[i].revents = non_event; } } bool Init() { _listensock.Socket(); _listensock.Bind(_port); _listensock.Listen(); return true; } void PrintFd() { std::cout << "online fd list:"; for (int i = 0; i < fd_num_max; i++) { if (_event_fds[i].fd == defaultfd) { continue; } else { std::cout << _event_fds[i].fd << "->"; } } std::cout << std::endl; } void Accepter() { // 连接事件就绪 uint16_t clientport; std::string clientip; // 在此处不会在阻塞了，因为selec已经告诉我事件已经就绪 int sock = _listensock.Accept(&clientip, &clientport); if (sock < 0) { return; } else { lg.logmessage(Info, "accept success! %s, %d", clientip.c_str(), clientport); // 这里不能直接读，因为读写事件不一定就绪，所以要直接把这里获取的sock交给select // 这里吧sock交给辅助数组就可以把sock交给select来监听了 int pos = 1; for (; pos < fd_num_max; pos++) { if (_event_fds[pos].fd != defaultfd) { continue; } else { break; } } // 这里跳出循环有两种情况，一是找到了没有设置的数组下标，二是数组满了 if (pos == fd_num_max) { lg.logmessage(Warning, "sorry, server is full, sockfd[%d] will close", sock); close(sock); // poll这里也可以进行扩容 } else { // 找到未被设置的下标了 _event_fds[pos].fd = sock; // 设置关心事件 _event_fds[pos].events = POLLIN | POLLOUT; _event_fds[pos].revents = non_event; PrintFd(); } } } void Recvr(int fd, int pos) { // 其他的文件描述符就绪,进行读取操作 char buffer[1024]; ssize_t n = read(fd, buffer, sizeof(buffer) - 1); if (n > 0) { buffer[n] = 0; std::cout << "get a message:" << buffer << std::endl; } else if (n == 0) { lg.logmessage(Info, "client quit, close fd is:%d", fd); _event_fds[pos].fd = defaultfd; close(fd); } else { lg.logmessage(Warning, "read error, fd is:%d", fd); _event_fds[pos].fd = defaultfd; close(fd); } } void Dispacter() { // 便利所有的文件描述符数组，因为我不知道哪一个就绪了 for (int i = 0; i < fd_num_max; i++) { int fd = _event_fds[i].fd; if (fd == defaultfd) { // 不是合法的文件描述符 continue; } if (_event_fds[i].revents & POLLIN) { if (_listensock.Fd() == fd) { // 连接管理器 Accepter(); } else { Recvr(fd, i); } } } } void Start() { _event_fds[0].fd = _listensock.Fd(); _event_fds[0].events = POLLIN; int timeout = 3000; for (;;) { int n = poll(_event_fds, fd_num_max, timeout); switch (n) { case 0: std::cout << "time out......" << std::endl; break; case -1: std::cout << "poll fail" << std::endl; break; default: // 有事件就绪 std::cout << "get a link" << std::endl; // 处理事件 Dispacter(); break; } } } ~PollServer() { _listensock.Close(); } private: Sock _listensock; uint16_t _port; struct pollfd _event_fds[fd_num_max]; };2.2 Log.hpp文件
#pragma once #include <iostream> #include <stdarg.h> #include <time.h> #include<sys/stat.h> #include<sys/types.h> #include<unistd.h> #include<stdlib.h> #include <fcntl.h> #include<string.h> #define SIZE 1024 // 设置日志等级 #define Info 0 #define Debug 1 #define Warning 2 #define Error 3 #define Fatal 4 #define Screen 1 #define Onefile 2 #define Classfile 3 #define logFile "log.txt" class log { public: log() { PrintMethod = Screen; path = "./log/"; } void Enable(int method) { PrintMethod = method; } std::string levelToString(int level) { switch (level) { case Info: return "Info"; case Debug: return "Debug"; case Warning: return "Warning"; case Error: return "Error"; default: return "None"; } } void logmessage(int level, const char *format, ...) // 后面的省略号表示可变参数 { char leftbuffer[SIZE]; time_t t = time(nullptr); struct tm *ctime = localtime(&t); snprintf(leftbuffer, sizeof(leftbuffer), "[%s],[%d-%d-%d %d:%d:%d]", levelToString(level).c_str(), ctime->tm_year + 1900, ctime->tm_mon, ctime->tm_mday, ctime->tm_hour, ctime->tm_min, ctime->tm_sec); char rightbuffer[SIZE]; va_list s; va_start(s, format); vsnprintf(rightbuffer, sizeof(rightbuffer), format, s); va_end(s); char logtxt[SIZE * 3]; snprintf(logtxt, sizeof(logtxt), "%s %s\n", leftbuffer, rightbuffer); // printf("%d-%d-%d %d:%d:%d\n",ctime->tm_year + 1900, ctime->tm_mon, ctime->tm_mday, ctime->tm_hour,ctime->tm_min,ctime->tm_sec); //printf("%s", logtxt); PrintLog(level,logtxt); // 格式：默认部分+自定义部分（可变参数部分） } void PrintLog(int level, const std::string& logtxt) { switch(PrintMethod) { case Screen: std::cout << logtxt << std::endl; break; case Onefile: printOneFile(logFile, logtxt); break; case Classfile: printClassFile(level, logtxt); break; default: break; } } void printOneFile(const std::string &logname, const std::string &logtxt) { std::string _logname = path + logname; int fd = open(_logname.c_str(),O_WRONLY|O_CREAT|O_APPEND,0666); if(fd < 0) { return ; } write(fd,logtxt.c_str(),logtxt.size()); close(fd); } void printClassFile(int level, const std::string &logtxt) { std::string filename = logFile; filename += "."; filename += levelToString(level); printOneFile(filename, logtxt); } ~log() { } private: int PrintMethod; std::string path; }; log lg;2.3 Sock.hpp文件
#pragma once #include <iostream> #include <string> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/socket.h> #include <arpa/inet.h> #include <netinet/in.h> #include <cstring> #include "Log.hpp" const int backlog = 10; extern log lg; enum { SocketError = 2, BindError, ListenError }; class Sock { public: Sock() : _sockfd(-1) { } ~Sock() { if (_sockfd >= 0) { close(_sockfd); } } // 创建套接字 void Socket() { _sockfd = socket(AF_INET, SOCK_STREAM, 0); if (_sockfd < 0) { lg.logmessage(Fatal, "socket fail, %s, %d", errno, strerror(errno)); exit(SocketError); } int opt = -1; setsockopt(_sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)); } // 创建一个绑定接口 void Bind(const uint16_t port) { 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(_sockfd, (struct sockaddr *)&local, sizeof(local)) < 0) { lg.logmessage(Fatal, "bind fail, %s, %d", errno, strerror(errno)); exit(BindError); } } void Listen() { if (listen(_sockfd, backlog) < 0) { lg.logmessage(Fatal, "listen fail, %s, %d", errno, strerror(errno)); exit(ListenError); } } int Accept(std::string *clientip, uint16_t *clientport) { struct sockaddr_in peer; socklen_t len = sizeof(peer); int newfd = accept(_sockfd, (struct sockaddr *)&peer, &len); if (newfd < 0) { lg.logmessage(Warning, "accept fail, %s, %d", errno, strerror(errno)); return -1; } char ipstr[64]; inet_ntop(AF_INET, &peer.sin_addr, ipstr, sizeof(ipstr)); // 获取远端主机的信息 *clientport = ntohs(peer.sin_port); *clientip = ipstr; return newfd; } bool Connect(const std::string &ip, const uint16_t &port) { struct sockaddr_in peer; memset(&peer, 0, sizeof(peer)); peer.sin_family = AF_INET; peer.sin_port = htons(port); inet_pton(AF_INET, ip.c_str(), &peer.sin_addr); int n = connect(_sockfd, (struct sockaddr *)&peer, sizeof(peer)); if (n == -1) { std::cerr << "connect to" << ip << ":" << port << std::endl; return false; } return true; } void Close() { close(_sockfd); } int Fd() { return _sockfd; } private: int _sockfd; };2.4main.cc文件
#include "PollServer.hpp" #include <memory> int main() { std::unique_ptr<PollServer> svr(new PollServer()); svr->Init(); svr->Start(); return 0; }三、poll的优缺点
3.1 poll的优点
(1)不同于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。
(2)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。
(3）poll并没有最大数量限制（但是数量过大后性能也是会下降）。
3.2 poll的缺点
当poll中监听的文件描述符数目增多时：
（1）poll和select函数一样，poll返回后，需要轮询pollfd来获取就绪的描述符。
（2）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。
（3）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。
