linux—epoll

一、epoll服务端实现中需要的3个函数：

• epoll_create：创建保存epoll文件描述符的空间。
• epoll_ctl：向空间注册并注销文件描述符。
• epoll_wait：与select函数类似，等待文件描述符发生变化。

二、示例

回声服务端：

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <sys/epoll.h>

 #define BUF_SIZE 1024
 #define EPOLL_SIZE 50
 void error_handling(char * messages);

 int main(int argc, char *argv[])
 {
     if(argc != )
     {
         printf("Usage : %s <port>\n", argv[]);
         exit();
     }
     int serverSock, clientSock;
     struct sockaddr_in serverAddr, clientAddr;
     socklen_t clientAddrSize;

     char buf[BUF_SIZE];
     int strLen;

     struct epoll_event *ep_events;
     struct epoll_event event;
     int epfd, event_cnt;

     serverSock =socket(PF_INET, SOCK_STREAM, );
     if(serverSock == -)
         error_handling("socket() error");

     memset(&serverAddr, , sizeof(serverAddr));
     serverAddr.sin_family = AF_INET;
     serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
     serverAddr.sin_port = htons(atoi(argv[]));

     if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -)
         error_handling("bind() error");
     if(listen(serverSock, ) == -)
         error_handling("listen() error");

     epfd = epoll_create(EPOLL_SIZE);
     ep_events = (struct epoll_event*)malloc(sizeof(struct epoll_event) * EPOLL_SIZE);

     event.events = EPOLLIN;
     event.data.fd = serverSock;
     epoll_ctl(epfd, EPOLL_CTL_ADD, serverSock, &event);

     puts("Server start...");
     while(){
         event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -);
         if(event_cnt == -){
             puts("epoll_wait() error");
             break;
         }
         for(int i = ; i < event_cnt; i++){
             if(ep_events[i].data.fd == serverSock){
                 clientAddrSize = sizeof(clientAddr);
                 clientSock = accept(serverSock, (struct sockaddr*)&clientAddr, &clientAddrSize);
                 event.events = EPOLLIN;
                 event.data.fd = clientSock;
                 epoll_ctl(epfd, EPOLL_CTL_ADD, clientSock, &event);
                 printf("connected client: %d\n", clientSock);
             }
             else{
                 strLen = read(ep_events[i].data.fd, buf, BUF_SIZE);
                 if(strLen == ){
                     epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL);
                     close(ep_events[i].data.fd);
                     printf("closed client: %d\n", ep_events[i].data.fd);
                 }
                 else{
                     write(ep_events[i].data.fd, buf, strLen);
                     puts("echo");
                 }
             }
         }
     }
     close(serverSock);
     puts("Server close...");
     return ;
 }

 void error_handling(char * messages)
 {
     puts(messages);
     exit();
 }

三、条件触发和边缘触发

　　条件触发方式中，只要输入缓冲有数据就会一直通知该事件。

　　边缘触发方式中输入缓冲收到数据时仅注册一次该事件。即使输入缓冲中还留有数据，也不会再进行注册。

　　select模型是以条件触发的方式工作的。

　　epoll默认是以条件触发方式工作的。

　　若将文件（套接字）改为非阻塞模式。调用read&write函数时，无论是否存在数据，都会形成非阻塞文件（套接字）。

　　边缘触发方式下，以阻塞方式工作的read&write函数又可能引起服务器端的长事件停顿。因此，边缘触发方式中一定要采用非阻塞read&write函数。

边缘触发的回声服务端：

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <sys/epoll.h>
 #include <fcntl.h>
 #include <errno.h>

 #define BUF_SIZE 4
 #define EPOLL_SIZE 50
 void setnonblockingmode(int fd);
 void error_handling(char * messages);

 int main(int argc, char *argv[])
 {
     if(argc != )
     {
         printf("Usage : %s <port>\n", argv[]);
         exit();
     }
     int serverSock, clientSock;
     struct sockaddr_in serverAddr, clientAddr;
     socklen_t clientAddrSize;

     char buf[BUF_SIZE];
     int strLen;

     struct epoll_event *ep_events;
     struct epoll_event event;
     int epfd, event_cnt;

     serverSock =socket(PF_INET, SOCK_STREAM, );
     if(serverSock == -)
         error_handling("socket() error");

     memset(&serverAddr, , sizeof(serverAddr));
     serverAddr.sin_family = AF_INET;
     serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
     serverAddr.sin_port = htons(atoi(argv[]));

     if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -)
         error_handling("bind() error");
     if(listen(serverSock, ) == -)
         error_handling("listen() error");

     epfd = epoll_create(EPOLL_SIZE);
     ep_events = (struct epoll_event*)malloc(sizeof(struct epoll_event) * EPOLL_SIZE);

     setnonblockingmode(serverSock);
     event.events = EPOLLIN;
     event.data.fd = serverSock;
     epoll_ctl(epfd, EPOLL_CTL_ADD, serverSock, &event);

     puts("Server start...");
     while(){
         event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -);
         if(event_cnt == -){
             puts("epoll_wait() error");
             break;
         }
         puts("return epoll_wait");
         for(int i = ; i < event_cnt; i++){
             if(ep_events[i].data.fd == serverSock){
                 clientAddrSize = sizeof(clientAddr);
                 clientSock = accept(serverSock, (struct sockaddr*)&clientAddr, &clientAddrSize);
                 setnonblockingmode(clientSock);
                 event.events = EPOLLIN|EPOLLET;
                 event.data.fd = clientSock;
                 epoll_ctl(epfd, EPOLL_CTL_ADD, clientSock, &event);
                 printf("connected client: %d\n", clientSock);
             }
             else{
                 while()
                 {
                     strLen = read(ep_events[i].data.fd, buf, BUF_SIZE);
                     if(strLen == ){
                         epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL);
                         close(ep_events[i].data.fd);
                         printf("closed client: %d\n", ep_events[i].data.fd);
                         break;
                     }
                     else if(strLen < ){
                         if(errno == EAGAIN)
                             break;
                         else
                             puts("???????");
                     }
                     else{
                         write(ep_events[i].data.fd, buf, strLen);
                     }
                 }
             }
         }
     }
     close(serverSock);
     puts("Server close...");
     return ;
 }

 void setnonblockingmode(int fd) // 套接字改成非阻塞的
 {
     int flag = fcntl(fd, F_GETFL, );
     fcntl(fd, F_SETFL, flag|O_NONBLOCK);
 }

 void error_handling(char * messages)
 {
     puts(messages);
     exit();
 }