任务：
实现一个TCP server的回声服务器，功能是将客户端发送的消息原样返回，应用epoll处理事件循环实现IO多路复用。借此任务理解IO多路复用应用的开发模式。
参考资料：
/linux/man-pages/man2/epoll_create1.2.html
/linux/man-pages/man2/epoll_wait.2.html
/linux/man-pages/man2/epoll_ctl.2.html
代码实现：
#include <stdio.h>#include <sys/socket.h>#include <sys/types.h>#include <netinet/in.h>#include <stdlib.h>#include <sys/epoll.h>#define LISTEN_BACKLOG 50#define BUFFER_SIZE 1024#define MAX_EVENTS 1024typedef struct efddata{void * ptr;int fd;uint64_t len;} efd_data;int main(int argc,char* argv[]){int sfd,cfd,epfd,nfds,n,r,w;char* buf[MAX_EVENTS];struct sockaddr_in addr_in = {0};// 创建epollepfd = epoll_create1(EPOLL_CLOEXEC);printf("epfd: %d\n",epfd);if (epfd == -1){perror("epoll_create1 fail");exit(EXIT_FAILURE);}// 创建监听socketsfd = socket(AF_INET,SOCK_STREAM | SOCK_NONBLOCK,0);printf("sfd: %d\n",sfd);if (sfd == -1){perror("socket fail");exit(EXIT_FAILURE);}addr_in.sin_family = AF_INET;addr_in.sin_port = htons(80);if(bind(sfd,(const struct sockaddr*)&addr_in,sizeof(struct sockaddr_in)) == -1){perror("bind fail");exit(EXIT_FAILURE);}if(listen(sfd,LISTEN_BACKLOG) == -1){perror("listen fail");exit(EXIT_FAILURE);}// 将监听socket的EPOLLIN事件加入队列struct epoll_event evt = {0};evt.events = EPOLLIN;evt.data.fd = sfd;if(epoll_ctl(epfd,EPOLL_CTL_ADD,sfd,&evt) == -1){perror("epoll_ctl add epfd fail");exit(EXIT_FAILURE);}// 预分配fd事件内存struct epoll_event events[MAX_EVENTS],*fdevents[MAX_EVENTS];for(n = 0; n < MAX_EVENTS; ++n){struct epoll_event *e = (struct epoll_event *)malloc(sizeof(struct epoll_event));if(e == NULL){perror("malloc");exit(EXIT_FAILURE);}fdevents[n] = e;}for(;;){nfds = epoll_wait(epfd,events,MAX_EVENTS,-1);if(nfds == -1){perror("epoll_wait fail");close(epfd);exit(EXIT_FAILURE);}for(n = 0; n < nfds; ++n){if(events[n].data.fd == sfd){ // 接受客户端连接cfd = accept(sfd,NULL,NULL);if (cfd == -1){fprintf(stderr,"accept fail %d\n",sfd);continue;}char * rbuf = (char *)malloc(BUFFER_SIZE);buf[cfd] = rbuf;efd_data* data = (efd_data *)malloc(sizeof(efd_data));data->ptr = buf[cfd];data->fd = cfd;struct epoll_event *e = fdevents[cfd];e->events = EPOLLIN;e->data.ptr = data;if(epoll_ctl(epfd,EPOLL_CTL_ADD,cfd,fdevents[cfd]) == -1){perror("epoll_ctl add fail");close(cfd);}fprintf(stdout,"accept cfd %d\n",cfd);}else{efd_data * data = (efd_data *)events[n].data.ptr; // 处理读事件if(events[n].events & EPOLLIN){fprintf(stdout,"epollin ready cfd %d\n",data->fd);r = read(data->fd,data->ptr,BUFFER_SIZE);if(r == -1){perror("read fail");if(epoll_ctl(epfd,EPOLL_CTL_DEL,data->fd,NULL) == -1){perror("epoll_ctl del fail");exit(EXIT_FAILURE);;}close(data->fd);}else{struct epoll_event *evt = fdevents[data->fd];evt->events = EPOLLOUT;((efd_data *)(evt->data.ptr))->len= r;if(epoll_ctl(epfd,EPOLL_CTL_MOD,data->fd,evt) == -1){perror("epoll_ctl mod epollout fail");}}}// 处理写事件if(events[n].events & EPOLLOUT){w = write(data->fd,data->ptr,data->len);if(w == -1){fprintf(stderr,"write fail to cfd:%d\n",data->fd);}epoll_ctl(epfd,EPOLL_CTL_DEL,data->fd,NULL);close(data->fd);fprintf(stdout,"write success cfd: %d\n",data->fd);}}}}}
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可以用go写一个tcp的客户端，模拟并发访问。
package mainimport ("flag""fmt""log""net""sync")var wg sync.WaitGroupfunc testEcho(n int) {defer wg.Done()con, err := net.Dial("tcp", "[192.168.171.134]:80")if err != nil {log.Fatal(err)}defer con.Close()msg := fmt.Sprintf("Hello epoll %d~", n)l, err := con.Write([]byte(msg))if err != nil {log.Fatal(err)}buffer := make([]byte, 1024)l, err = con.Read(buffer)if err != nil {log.Fatal(err)}log.Println(string(buffer[0:l]))}var n = flag.Int("n", 100, "set the max test count")func main() {flag.Parse()log.Println("start\n")for i := 0; i < *n; i++ {wg.Add(1)go testEcho(i)}wg.Wait()log.Println("End\n")}
View Code
执行效果：
经过这个过程，可以更加深刻的理解epoll的工作原理，对于理解redis和nginx的IO多路复用机制很有帮助~
