一、基本知識html
epoll是在2.6內核中提出的(mac沒有),是以前的select和poll的加強版本。相對於select和poll來講,epoll更加靈活,沒有描述符限制。epoll使用一個文件描述符管理多個描述符,將用戶關係的文件描述符的事件存放到內核的一個事件表中,這樣在用戶空間和內核空間的copy 只需一次。linux
==>內核事件表??
服務器
二、epoll接口併發
epoll操做過程須要三個接口,分別以下:llinux 系統 $man epoll 查看是否支持epoll
curl
#include <sys/epoll.h> int epoll_create(int size); int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event); int epoll_wait(int epfd, struct epoll_event * events, int maxevents, int timeout);
(1) int epoll_create(int size);
建立一個epoll的句柄,size用來告訴內核這個監聽的數目一共有多大。這個參數不一樣於select()中的第一個參數,給出最大監聽的fd+1的值。須要注意的是,當建立好epoll句柄後,它就是會佔用一個fd值,在linux下若是查看/proc/進程id/fd/,是可以看到這個fd的,所 以在使用完epoll後,必須調用close()關閉,不然可能致使fd被耗盡。socket
==》 cd /proc/進程id/fd //fd 目錄存儲進程佔用的文件描述符tcp
2)int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
epoll的事件註冊函數,它不一樣與select()是在監聽事件時告訴內核要監聽什麼類型的事件epoll的事件註冊函數,它不一樣與select()是在監聽事件時告訴內核要監聽什麼類型的事件,而是在這裏先註冊要監聽的事件類型。第一個參數是epoll_create()的返回值,函數
第二個參數表示動做,用三個宏來表示:
EPOLL_CTL_ADD:註冊新的fd到epfd中;
EPOLL_CTL_MOD:修改已經註冊的fd的監聽事件;
EPOLL_CTL_DEL:從epfd中刪除一個fd;
第三個參數是須要監聽的fd(文件,socket, STDIN_FILENO....)
測試
第四個參數是告訴內核須要監聽什麼事,struct epoll_event結構以下:ui
typedef union epoll_data{ void *ptr; int fd; __uint32_t u32; __uint64_t u64; } epoll_data_t; struct epoll_event { __uint32_t events; /* Epoll events */ epoll_data_t data; /* User data variable */ };
events能夠是如下幾個宏的集合:
EPOLLIN :表示對應的文件描述符能夠讀(包括對端SOCKET正常關閉);
EPOLLOUT:表示對應的文件描述符能夠寫;
EPOLLPRI:表示對應的文件描述符有緊急的數據可讀(這裏應該表示有帶外數據到來);
EPOLLERR:表示對應的文件描述符發生錯誤;
EPOLLHUP:表示對應的文件描述符被掛斷;
EPOLLET: 將EPOLL設爲邊緣觸發(Edge Triggered)模式,這是相對於水平觸發(Level Triggered)來講的。
EPOLLONESHOT:只監聽一次事件,當監聽完此次事件以後,若是還須要繼續監聽這個socket的話,須要再次把這個socket加入到EPOLL隊列裏
struct epoll_event ev; // init a event ev.events = EPOLLIN; ev.data.fd = fd;
3) int epoll_wait(int epfd, struct epoll_event * events, int maxevents, int timeout);
等待事件的產生,相似於select()調用。參數events用來從內核獲得事件的集合,maxevents告以內核這個events有多大,這個 maxevents的值不能大於建立epoll_create()時的size,參數timeout是超時時間(毫秒,0會當即返回,-1將不肯定,也有 說法說是永久阻塞)。該函數返回須要處理的事件數目,如返回0表示已超時。
三、工做模式
epoll對文件描述符的操做有兩種模式:LT(level trigger)和ET(edge trigger)。LT模式是默認模式,LT模式與ET模式的區別以下:
LT模式:當epoll_wait檢測到描述符事件發生並將此事件通知應用程序,應用程序能夠不當即處理該事件。下次調用epoll_wait時,會再次響應應用程序並通知此事件。
ET模式:當epoll_wait檢測到描述符事件發生並將此事件通知應用程序,應用程序必須當即處理該事件。若是不處理,下次調用epoll_wait時,不會再次響應應用程序並通知此事件。
ET模式在很大程度上減小了epoll事件被重複觸發的次數,所以效率要比LT模式高。epoll工做在ET模式的時候,必須使用非阻塞套接口,以免因爲一個文件句柄的阻塞讀/阻塞寫操做把處理多個文件描述符的任務餓死。
四、測試程序
編寫一個服務器回射程序echo,練習epoll過程。
服務器代碼以下所示:
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <netinet/in.h> #include <sys/socket.h> #include <arpa/inet.h> #include <sys/epoll.h> #include <unistd.h> #include <sys/types.h> #define IPADDRESS "127.0.0.1" #define PORT 8787 #define MAXSIZE 1024 //read maxsize #define LISTENQ 5 // #define FDSIZE 1000 #define EPOLLEVENTS 100 //綁定socket static int socket_bind(const char* ip, int port); //IO多路服用處理epoll static void do_epoll(int listenfd); //處理響應的事件 static void handle_events(int epollfd,struct epoll_event* events, int num,int listenfd, char* buf); //讀、寫、監聽事件 static void handle_accept(int epollfd, int listenfd); static void do_read(int epollfd, int listenfd, char* buf); static void do_write(int epollfd, int listenfd, char* buf); //註冊監聽fd static void add_event(int epollfd, int fd, int state); static void modify_event(int epollfd, int fd, int state); static void delete_event(int epollfd, int fd, int state); // change epoll contains differerents listenfd int main(int argc, char** argv) { int listenfd; listenfd = socket_bind(IPADDRESS, PORT); listen(listenfd, LISTENQ); do_epoll(listenfd); return 0; } static int socket_bind(const char* ip, int port) { int listenfd; struct sockaddr_in servaddr; listenfd = socket(AF_INET, SOCK_STREAM,0); if(listenfd == -1) { perror("socket error.\n"); exit(0); } bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; inet_pton(AF_INET, ip,&servaddr.sin_addr); servaddr.sin_port = htons(port); if(bind(listenfd, (struct sockaddr*)&servaddr,sizeof(servaddr)) == -1) { perror("bind error.\n"); exit(1); } return listenfd; } static void do_epoll(int listenfd) { int epollfd; struct epoll_event events[EPOLLEVENTS]; int ret; char buf[MAXSIZE]; memset(buf,0,MAXSIZE); epollfd = epoll_create(FDSIZE); add_event(epollfd, listenfd, EPOLLIN); //本地端口監聽時間,可讀 for(;;) { ret = epoll_wait(epollfd, events,EPOLLEVENTS,-1); handle_events(epollfd, events,ret, listenfd,buf); } close(epollfd); //關閉epollfd, } static void handle_events(int epollfd, struct epoll_event* events, int num, int listenfd, char* buf) { int i; int fd; for( i=0; i<num; i++) { fd = events[i].data.fd; if( (fd == listenfd) && (events[i].events & EPOLLIN)) //處理接受連接事件 handle_accept(epollfd, listenfd); else if (events[i].events & EPOLLIN) do_read(epollfd, fd, buf); else if (events[i].events & EPOLLOUT) do_write(epollfd, fd, buf); //echo } } static void handle_accept(int epollfd, int listenfd) { int clifd; struct sockaddr_in cliaddr; socklen_t cliaddrlen; //若是不初始化,可能出現arguent error bzero(&cliaddr,sizeof(cliaddr)); cliaddrlen = sizeof(cliaddr); clifd = accept(listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen); if(clifd == -1) perror("accept error.\n"); else { printf("accept a new client:%s:%d\n",inet_ntoa(cliaddr.sin_addr),cliaddr.sin_port); add_event(epollfd, clifd, EPOLLIN); //從cliaddr端口, 可讀 } } static void do_read(int epollfd, int fd, char* buf) { int nread; nread = read(fd, buf, MAXSIZE); if(nread == -1) { perror("read error.\n"); close(fd); delete_event(epollfd,fd, EPOLLIN); } else if (nread == 0) { fprintf(stderr,"client close.\n"); close(fd); delete_event(epollfd, fd, EPOLLIN); } else { printf("read message is: %s",buf); modify_event(epollfd, fd, EPOLLOUT); //實現echo處理 } } static void do_write(int epollfd, int fd, char* buf) { int nwrite; nwrite = write(fd, buf, strlen(buf)); if(nwrite == -1) { perror("write error:"); close(fd); delete_event(epollfd, fd, EPOLLOUT); } else { modify_event(epollfd, fd, EPOLLIN); memset(buf, 0, MAXSIZE); //寫完清空 } } static void add_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev); } static void modify_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &ev); } static void delete_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &ev); }
客戶端也用epoll實現,控制STDIN_FILENO、STDOUT_FILENO、和sockfd三個描述符,程序以下所示:
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <netinet/in.h> #include <sys/epoll.h> #include <time.h> #include <unistd.h> #include <sys/types.h> #include <arpa/inet.h> #define MAXSIZE 1024 #define IPADDRESS "127.0.0.1" #define SERV_PORT 8787 #define FDSIZE 1024 #define EPOLLEVENTS 20 static void handle_connection(int sockfd); static void handle_events(int epollfd, struct epoll_event* event, int num, int sockfd, char* buf); static void do_read(int epollfd, int fd, int sockfd, char* buf); static void do_write(int epollfd, int fd, int sockfd, char* buf); static void add_event(int epollfd, int fd, int state); static void modify_event(int epollfd, int fd, int state); static void delete_event(int epollfd, int fd, int state); int main(int argc, char**argv) { int sockfd; struct sockaddr_in servaddr; sockfd = socket(AF_INET, SOCK_STREAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(SERV_PORT); inet_pton(AF_INET, IPADDRESS, &servaddr.sin_addr); connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)); //連接服務器 handle_connection(sockfd); //處理連接 close(sockfd); return 0; } static void handle_connection(int sockfd) { int epollfd; struct epoll_event events[EPOLLEVENTS]; char buf[MAXSIZE]; int ret; epollfd = epoll_create(FDSIZE); add_event(epollfd, STDIN_FILENO, EPOLLIN); //從標準輸入讀取 for(;;) { ret = epoll_wait(epollfd, events, EPOLLEVENTS, -1); handle_events(epollfd, events, ret, sockfd, buf); } close(epollfd); //關閉epollfd } static void handle_events(int epollfd, struct epoll_event* events, int num, int sockfd, char* buf) { int fd; int i; for(i=0; i<num; i++) { fd = events[i].data.fd; if(events[i].events & EPOLLIN) do_read(epollfd, fd, sockfd, buf); else if(events[i].events & EPOLLOUT) do_write(epollfd, fd, sockfd, buf); } } static void do_read(int epollfd, int fd, int sockfd, char* buf) { int nread; nread = read(fd, buf, MAXSIZE); if(nread == -1) { perror("read error.\n"); close(fd); } else if(nread == 0) { fprintf(stderr,"server close.\n"); close(fd); } else { if(fd == STDIN_FILENO) add_event(epollfd, sockfd, EPOLLOUT); //從STDIN_FILENO 讀取結束後,準備向sockfd寫入 else { delete_event(epollfd, sockfd, EPOLLIN); //從sockfd讀取結束, add_event(epollfd, STDOUT_FILENO, EPOLLOUT); //添加STDOUT_FILENO輸出 } } } static void do_write(int epollfd, int fd, int sockfd, char* buf) { int nwrite; nwrite = write(fd, buf, strlen(buf)); //strlen() 字符串未滿 if(nwrite == -1) { perror("write error.\n"); close(fd); } else { if(fd == STDOUT_FILENO) delete_event(epollfd, fd, EPOLLOUT); else modify_event(epollfd, fd, EPOLLIN); //向sockfd寫完,添加等待讀取事件 } memset(buf,0,MAXSIZE); //清空 } static void add_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev); } static void modify_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &ev); } static void delete_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &ev); }
參考資料:
http://www.cnblogs.com/OnlyXP/archive/2007/08/10/851222.html
http://www.cnblogs.com/lexus/archive/2011/11/19/2254798.html
https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/
epoll 實現的同時處理 監聽TCP,UDP的 併發 服務器代碼:
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <netinet/in.h> #include <sys/socket.h> #include <arpa/inet.h> #include <sys/epoll.h> #include <unistd.h> #include <sys/types.h> #include <errno.h> #define IPADDRESS "127.0.0.1" #define TCP_PORT 8787 #define UDP_PORT 8989 #define MAXSIZE 1024 #define LISTENQ 5 #define FDSIZE 1000 #define EPOLLEVENTS 100 static void handle_events(int epollfd,struct epoll_event* events, int num, int tcpfd, int udpfd, char* buf); static void handle_accept(int epollfd, int tcpfd); static void do_read(int epollfd, int listenfd, char* buf); static void do_write(int epollfd, int listenfd, char* buf); //處理數據轉發 static void tcp_read(int epollfd, int fd, char* buf); static void udp_read(int epollfd, int fd, char* buf); static void add_event(int epollfd, int fd, int state); static void modify_event(int epollfd, int fd, int state); static void delete_event(int epollfd, int fd, int state); // change epoll contains differerents listenfd int main(int argc, char** argv) { int tcpfd,udpfd; struct sockaddr_in servaddr,addr; int epollfd; struct epoll_event events[EPOLLEVENTS]; int ret; char buf[MAXSIZE]; memset(buf,0,MAXSIZE); //tcp socket tcpfd = socket(AF_INET, SOCK_STREAM,0); if(tcpfd == -1) { perror("tcp socket error.\n"); exit(0); } bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; inet_pton(AF_INET, IPADDRESS,&servaddr.sin_addr); servaddr.sin_port = htons(TCP_PORT); if(bind(tcpfd, (struct sockaddr*)&servaddr,sizeof(servaddr)) == -1) { perror("bind tcpfd error.\n"); exit(1); } //udp socket udpfd = socket(AF_INET, SOCK_DGRAM,0); if(udpfd == -1) { perror("udp socket error.\n"); exit(1); } bzero(&addr, sizeof(addr)); addr.sin_family = AF_INET; inet_pton(AF_INET, IPADDRESS, &addr.sin_addr); addr.sin_port = htons(UDP_PORT); if(bind(udpfd, (struct sockaddr*)&addr, sizeof(addr)) == -1) { perror("bind udpfd error.\n"); exit(1); } /* while(1) { memset(buf,0,MAXSIZE); if(recvfrom(udpfd, buf, MAXSIZE, 0, NULL, NULL) == -1) { printf("recv error.\n"); exit(1); } printf("recv:%s\n",buf); } */ listen(tcpfd, LISTENQ); epollfd = epoll_create(FDSIZE); add_event(epollfd, tcpfd, EPOLLIN); add_event(epollfd, udpfd, EPOLLIN); for(;;) { ret = epoll_wait(epollfd, events,EPOLLEVENTS,-1); handle_events(epollfd, events, ret, tcpfd, udpfd,buf); } close(epollfd); return 0; } static void handle_events(int epollfd, struct epoll_event* events, int num, int tcpfd, int udpfd, char* buf) { int i; int fd; for( i=0; i<num; i++) { fd = events[i].data.fd; printf("num:%d,fd:%d,tcpfd:%d,udp:%d\n",num,fd,tcpfd,udpfd); if((fd == tcpfd) && (events[i].events & EPOLLIN)) { //獲取新的TCP連接 handle_accept(epollfd, tcpfd); } else if((fd == udpfd) && (events[i].events & EPOLLIN)) { //接收UDP數據 udp_read(epollfd, fd, buf); } else if((fd == udpfd) && (events[i].events & EPOLLOUT)) { //udp端口echo } else if ((fd != udpfd) && (events[i].events & EPOLLIN)) { //接受普通端口數據 tcp_read(epollfd, fd, buf); } else if ((fd != udpfd) && (events[i].events & EPOLLOUT)) { //do_write(epollfd, fd, buf); } else { //處理其餘事件 } } } static void handle_accept(int epollfd, int listenfd) { int clifd; struct sockaddr_in cliaddr; socklen_t cliaddrlen; //若是不初始化,可能出現arguent error bzero(&cliaddr,sizeof(cliaddr)); cliaddrlen = sizeof(cliaddr); clifd = accept(listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen); if(clifd == -1) perror("accept error.\n"); else { printf("accept a new tcp:%s:%d\n",inet_ntoa(cliaddr.sin_addr),cliaddr.sin_port); add_event(epollfd, clifd, EPOLLIN); } } static void tcp_read(int epollfd, int fd, char* buf) { int nread; nread = read(fd, buf, MAXSIZE); if(nread <= 0) { fprintf(stderr,"tcp error.\n"); close(fd); delete_event(epollfd, fd, EPOLLIN); } else { //to-do curl printf("recv tcp: %s\n",buf); } // close(fd); // delete_event(epollfd, fd, EPOLLIN); // add_event(epollfd, fd, EPOLLIN); memset(buf,0,MAXSIZE); } static void udp_read(int epollfd, int fd, char* buf) { int nread; struct sockaddr_in cliaddr; socklen_t cliaddrlen; //若是不初始化,可能出現arguent error bzero(&cliaddr,sizeof(cliaddr)); cliaddrlen = sizeof(cliaddr); nread=recvfrom(fd, buf, MAXSIZE,0,(struct sockaddr*)&cliaddr, &cliaddrlen); if(nread <= 0) { fprintf(stderr,"udp error.\n"); } else { //to-do curl printf("recv udp: %s\n",buf); } memset(buf,0,MAXSIZE); } static void do_read(int epollfd, int fd, char* buf) { int nread; nread = read(fd, buf, MAXSIZE); if(nread == -1) { perror("read error.\n"); close(fd); delete_event(epollfd,fd, EPOLLIN); } else if (nread == 0) { fprintf(stderr,"client close.\n"); close(fd); delete_event(epollfd, fd, EPOLLIN); } else { printf("read message is: %s",buf); modify_event(epollfd, fd, EPOLLOUT); } } static void do_write(int epollfd, int fd, char* buf) { int nwrite; nwrite = write(fd, buf, strlen(buf)); if(nwrite == -1) { perror("write error:"); close(fd); delete_event(epollfd, fd, EPOLLOUT); } else { modify_event(epollfd, fd, EPOLLIN); } memset(buf, 0, MAXSIZE); } static void add_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev); } static void modify_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &ev); } static void delete_event(int epollfd, int fd, int state) { struct epoll_event ev; ev.events = state; ev.data.fd = fd; epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &ev); }