epoll学习（二）
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当一个进程调用epoll_create时，内核会创建一个struct eventpoll。这个结构体有两个成员与epoll的使用方式密切相关。
struct eventpoll { ........ /* List of ready file descriptors */ //双向链表rdllist保存着通过epoll_wait返回给用户的、满足条件的事件 struct list_head rdllist; /* RB tree root used to store monitored fd structs */ //红黑树根节点保存所有要监控的事件 struct rb_root rbr; ........... };每一个epoll对象都有一个独立的eventpoll结构体，这个结构体会在内核空间创造独立的内存，用于存储使用epoll_ctl向epoll对象添加的事件，这些事件会挂到rbr红黑树中，重复添加的的事件就可通过红黑树识别，在epoll中每个事件都会建立一个epitem结构体，
/* * Each file descriptor added to the eventpoll interface will * have an entry of this type linked to the "rbr" RB tree. */ struct epitem { /* RB tree node used to link this structure to the eventpoll RB tree */ struct rb_node rbn; /* List header used to link this structure to the eventpoll ready list */ struct list_head rdllink; /* * Works together "struct eventpoll"->ovflist in keeping the * single linked chain of items. */ struct epitem *next; /* The file descriptor information this item refers to */ //事件句柄信息 struct epoll_filefd ffd; /* Number of active wait queue attached to poll operations */ int nwait; /* List containing poll wait queues */ struct list_head pwqlist; /* The "container" of this item */ //指向所属的epoll对象 struct eventpoll *ep; /* List header used to link this item to the "struct file" items list */ struct list_head fllink;};此外，epoll还维护一个双链表，用于存储发生的事件，当epoll_wait调用时，仅仅观察这个list链表的eptime即可，有数据就返回，没数据就sleep，而且通常要监控百万级的句柄，大多一次返回很少量就绪的句柄，epoll_wait仅需从内核copy少量的句柄到用户态。
维护list链表：当执行epoll_ctl时，除了把socket放到epoll文件系统file对象对应的红黑树上外，还会给内核中断处理函数注册一个回调函数，告诉内核，如果这个句柄到了就调用回调函数把句柄放入list链表，所以当一个socket上有数据，内核就把socket从网卡copy到内核后就把socket插入到就绪链表里。
epoll实现需要一棵红黑树，一个准备就绪句柄链表，少量内核缓存，就能解决大并发socket问题， 执行epoll_create创建红黑树和就绪链表，执行epoll_ctl，就增加socket句柄，则检查红黑树中是否存在，存在就返回，不存在就添加到树干上，然后向内核注册回调函数，用于当数据到来中断处理来临时向准备链表插入数据，执行epoll_wait时返回就绪链表里的数据。
epoll框架：
for( ; ; ){ndfs = epoll_wait(efpd, events, 20, 500);for(i = 0; i < ndfs; i++){if(events[i].data.fd == listened) //遍历所有端口有新连接{connfd = accept(listened, (sockaddr*)&clientaddr, &clilen);//接受连接ev.data.fd = connfd;ev.events = EPOLLIN|EPOLLET;epoll_ctl(epfd, EPOLL_CTL_ADD, sockfd, &ev);//将新的描述符添加到epoll监控队列}else if (events[i].events & EPOLLIN) //接收数据，读socket{n = read(sockfd, line, MAXLINE);ev.ptr.data = md ;ev.events = EPOLLOUT|EPOLLET;epoll_ctl(epfd, EPOLL_CTL_MOD, socketfd, &ev);//修改描述符等待下次循环发送数据}else if(events[i].events& EPOLLOUT){struct myepoll_data *md = (struct mypoll_data*)events[i].data.ptr;//取数据sockfd = md->fd ;send(sockfd, md->ptr, strlen((char*)md->ptr),0); //发送数据ev.data.fd = sockfd;ev.events = EPOLLIN|EPOLLOUT;epoll_ctl(epfd,EPOLL_CTL_MOD, sockfd, &ev);//修改描述符等待下次接受}else｛｝}}应用：
2. // a simple echo server using epoll in linux 3. // 4. 9. #include <sys/socket.h> 10. #include <sys/epoll.h> 11. #include <netinet/in.h> 12. #include <arpa/inet.h> 13. #include <fcntl.h> 14. #include <unistd.h> 15. #include <stdio.h> 16. #include <errno.h> 17. #include <iostream> 18. using namespace std; 19. #define MAX_EVENTS 500 20. struct myevent_s 21. { 22. int fd; 23. void (*call_back)(int fd, int events, void *arg); 24. int events; 25. void *arg; 26. int status; // 1: in epoll wait list, 0 not in 27. char buff[128]; // recv data buffer 28. int len, s_offset; 29. long last_active; // last active time 30. }; 31. // set event 32. void EventSet(myevent_s *ev, int fd, void (*call_back)(int, int, void*), void *arg) 33. { 34. ev->fd = fd; 35. ev->call_back = call_back; 36. ev->events = 0; 37. ev->arg = arg; 38. ev->status = 0; 39. bzero(ev->buff, sizeof(ev->buff)); 40. ev->s_offset = 0; 41. ev->len = 0; 42. ev->last_active = time(NULL); 43. } 44. // add/mod an event to epoll 45. void EventAdd(int epollFd, int events, myevent_s *ev) 46. { 47. struct epoll_event epv = {0, {0}}; 48. int op; 49. epv.data.ptr = ev; 50. epv.events = ev->events = events; 51. if(ev->status == 1){ 52. op = EPOLL_CTL_MOD; 53. } 54. else{ 55. op = EPOLL_CTL_ADD; 56. ev->status = 1; 57. } 58. if(epoll_ctl(epollFd, op, ev->fd, &epv) < 0) 59. printf("Event Add failed[fd=%d], evnets[%d]\n", ev->fd, events); 60. else 61. printf("Event Add OK[fd=%d], op=%d, evnets[%0X]\n", ev->fd, op, events); 62. } 63. // delete an event from epoll 64. void EventDel(int epollFd, myevent_s *ev) 65. { 66. struct epoll_event epv = {0, {0}}; 67. if(ev->status != 1) return; 68. epv.data.ptr = ev; 69. ev->status = 0; 70. epoll_ctl(epollFd, EPOLL_CTL_DEL, ev->fd, &epv); 71. } 72. int g_epollFd; 73. myevent_s g_Events[MAX_EVENTS+1]; // g_Events[MAX_EVENTS] is used by listen fd 74. void RecvData(int fd, int events, void *arg); 75. void SendData(int fd, int events, void *arg); 76. // accept new connections from clients 77. void AcceptConn(int fd, int events, void *arg) 78. { 79. struct sockaddr_in sin; 80. socklen_t len = sizeof(struct sockaddr_in); 81. int nfd, i; 82. // accept 83. if((nfd = accept(fd, (struct sockaddr*)&sin, &len)) == -1) 84. { 85. if(errno != EAGAIN && errno != EINTR) 86. { 87. } 88. printf("%s: accept, %d", __func__, errno); 89. return; 90. } 91. do 92. { 93. for(i = 0; i < MAX_EVENTS; i++) 94. { 95. if(g_Events[i].status == 0) 96. { 97. break; 98. } 99. } 100. if(i == MAX_EVENTS) 101. { 102. printf("%s:max connection limit[%d].", __func__, MAX_EVENTS); 103. break; 104. } 105. // set nonblocking 106. int iret = 0; 107. if((iret = fcntl(nfd, F_SETFL, O_NONBLOCK)) < 0) 108. { 109. printf("%s: fcntl nonblocking failed:%d", __func__, iret); 110. break; 111. } 112. // add a read event for receive data 113. EventSet(&g_Events[i], nfd, RecvData, &g_Events[i]); 114. EventAdd(g_epollFd, EPOLLIN, &g_Events[i]); 115. }while(0); 116. printf("new conn[%s:%d][time:%d], pos[%d]\n", inet_ntoa(sin.sin_addr), 117. ntohs(sin.sin_port), g_Events[i].last_active, i); 118. } 119. // receive data 120. void RecvData(int fd, int events, void *arg) 121. { 122. struct myevent_s *ev = (struct myevent_s*)arg; 123. int len; 124. // receive data 125. len = recv(fd, ev->buff+ev->len, sizeof(ev->buff)-1-ev->len, 0); 126. EventDel(g_epollFd, ev); 127. if(len > 0) 128. { 129. ev->len += len; 130. ev->buff[len] = '\0'; 131. printf("C[%d]:%s\n", fd, ev->buff); 132. // change to send event 133. EventSet(ev, fd, SendData, ev); 134. EventAdd(g_epollFd, EPOLLOUT, ev); 135. } 136. else if(len == 0) 137. { 138. close(ev->fd); 139. printf("[fd=%d] pos[%d], closed gracefully.\n", fd, ev-g_Events); 140. } 141. else 142. { 143. close(ev->fd); 144. printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno)); 145. } 146. } 147. // send data 148. void SendData(int fd, int events, void *arg) 149. { 150. struct myevent_s *ev = (struct myevent_s*)arg; 151. int len; 152. // send data 153. len = send(fd, ev->buff + ev->s_offset, ev->len - ev->s_offset, 0); 154. if(len > 0) 155. { 156. printf("send[fd=%d], [%d<->%d]%s\n", fd, len, ev->len, ev->buff); 157. ev->s_offset += len; 158. if(ev->s_offset == ev->len) 159. { 160. // change to receive event 161. EventDel(g_epollFd, ev); 162. EventSet(ev, fd, RecvData, ev); 163. EventAdd(g_epollFd, EPOLLIN, ev); 164. } 165. } 166. else 167. { 168. close(ev->fd); 169. EventDel(g_epollFd, ev); 170. printf("send[fd=%d] error[%d]\n", fd, errno); 171. } 172. } 173. void InitListenSocket(int epollFd, short port) 174. { 175. int listenFd = socket(AF_INET, SOCK_STREAM, 0); 176. fcntl(listenFd, F_SETFL, O_NONBLOCK); // set non-blocking 177. printf("server listen fd=%d\n", listenFd); 178. EventSet(&g_Events[MAX_EVENTS], listenFd, AcceptConn, &g_Events[MAX_EVENTS]); 179. // add listen socket 180. EventAdd(epollFd, EPOLLIN, &g_Events[MAX_EVENTS]); 181. // bind & listen 182. sockaddr_in sin; 183. bzero(&sin, sizeof(sin)); 184. sin.sin_family = AF_INET; 185. sin.sin_addr.s_addr = INADDR_ANY; 186. sin.sin_port = htons(port); 187. bind(listenFd, (const sockaddr*)&sin, sizeof(sin)); 188. listen(listenFd, 5); 189. } 190. int main(int argc, char **argv) 191. { 192. unsigned short port = 12345; // default port 193. if(argc == 2){ 194. port = atoi(argv[1]); 195. } 196. // create epoll 197. g_epollFd = epoll_create(MAX_EVENTS); 198. if(g_epollFd <= 0) printf("create epoll failed.%d\n", g_epollFd); 199. // create & bind listen socket, and add to epoll, set non-blocking 200. InitListenSocket(g_epollFd, port); 201. // event loop 202. struct epoll_event events[MAX_EVENTS]; 203. printf("server running:port[%d]\n", port); 204. int checkPos = 0; 205. while(1){ 206. // a simple timeout check here, every time 100, better to use a mini-heap, and add timer event 207. long now = time(NULL); 208. for(int i = 0; i < 100; i++, checkPos++) // doesn't check listen fd 209. { 210. if(checkPos == MAX_EVENTS) checkPos = 0; // recycle 211. if(g_Events[checkPos].status != 1) continue; 212. long duration = now - g_Events[checkPos].last_active; 213. if(duration >= 60) // 60s timeout 214. { 215. close(g_Events[checkPos].fd); 216. printf("[fd=%d] timeout[%d--%d].\n", g_Events[checkPos].fd, g_Events[checkPos].last_active, now); 217. EventDel(g_epollFd, &g_Events[checkPos]); 218. } 219. } 220. // wait for events to happen 221. int fds = epoll_wait(g_epollFd, events, MAX_EVENTS, 1000); 222. if(fds < 0){ 223. printf("epoll_wait error, exit\n"); 224. break; 225. } 226. for(int i = 0; i < fds; i++){ 227. myevent_s *ev = (struct myevent_s*)events[i].data.ptr; 228. if((events[i].events&EPOLLIN)&&(ev->events&EPOLLIN)) // read event 229. { 230. ev->call_back(ev->fd, events[i].events, ev->arg); 231. } 232. if((events[i].events&EPOLLOUT)&&(ev->events&EPOLLOUT)) // write event 233. { 234. ev->call_back(ev->fd, events[i].events, ev->arg); 235. } 236. } 237. } 238. // free resource 239. return 0; 240. } 0 0
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