1.Begins~
有的人学习linux编程很久，只知道网络编程是socket，bind， listen。。。，然而这些都是网络通信软件最基本的接口。在某网络公司待了y，也了解到公司的基础就是网络转发 ，然而网络转发实现并非我们平时所见的简单的send，recv。公司设备的转发都是建立在稳定并且高效的内部业务的基础上的，例如一个可靠性的服务：BFD(链路双向快速检测)，进程内业务就是建立在内核与用户态，后台处理与前台配置交互的过程上实现。在做项目的日子里，渐渐的对公司BFD模块有一定了解，特别是涉及到框架的地方，仔细看发现，一些技巧其实就是我们平日所用的技能外加一些优化。对于单进程用户态来说，处理前台进程交互与内核上送消息，如果没有一个高效的机制，是很难处理上以千计甚至万计的消息的。在参看公司代码的初始化阶段，发现一共用了至少3 个epoll回调机制，一个是处理前台发送的配置及查询，一个是处理与其他应用模块的交互，另一个是向其他应用通报状态变化的机制。公司的epoll_event 机制不知道是不是修改了内核，结构大致是这样：
typedef struct epoll_event { uint32_t events; // Epoll events epoll_data_t data; // User data variable ep_callback callback; /* 这跟linux内核不一样 ？ */}EPOLL_PACK; /*在添加epoll事件的时候就多了一个回调函数注册，这个十分方便了，回调函数可以用一个全局变量搞定，一个框架搭好，随后添加就大大的简单多了*/实际内核提供给我们使用的用户态结构是这样：
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 }; 不过我们也可以将epoll_data_t这个联合体封装在一个结构，只需要用指针*ptr指向封装的带fd及回调函数就可以。打算自己学习一些必要的技能，暂且就记录一下吧
2.Epoll API
extern int epoll_create(int size);extern int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);extern int epoll_wait(int epfd, struct epoll_event* events, int maxevents, int timeout);① int epoll_create(int size); 创建一个epoll的句柄。自从linux2.6.8之后，size参数是被忽略的。需要注意的是，当创建好epoll句柄后， 它就是会占用一个fd值，在linux下如果查看/proc/进程id/fd/，是能够看到这个fd的，所以在使用完epoll 后，必须调用close()关闭，否则可能导致fd被耗尽。 ②int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event); epoll的事件注册函数，它不同于select()是在监听事件时告诉内核要监听什么类型的事件，而是在这里先 注册要监听的事件类型。 参数： 第一个参数是epoll_create()的返回值。 第二个参数表示动作，用三个宏来表示： EPOLL_CTL_ADD：注册新的fd到epfd中； EPOLL_CTL_MOD：修改已经注册的fd的监听事件； EPOLL_CTL_DEL：从epfd中删除一个fd； 第三个参数是需要监听的fd。 第四个参数是告诉内核需要监听什么事，struct epoll_event结构如下：
enum EPOLL_EVENTS{
EPOLLIN = 0x001,
#define EPOLLIN EPOLLIN
EPOLLPRI = 0x002,
#define EPOLLPRI EPOLLPRI
EPOLLOUT = 0x004,
#define EPOLLOUT EPOLLOUT
EPOLLRDNORM = 0x040,
#define EPOLLRDNORM EPOLLRDNORM
EPOLLRDBAND = 0x080,
#define EPOLLRDBAND EPOLLRDBAND
EPOLLWRNORM = 0x100,
#define EPOLLWRNORM EPOLLWRNORM
EPOLLWRBAND = 0x200,
#define EPOLLWRBAND EPOLLWRBAND
EPOLLMSG = 0x400,
#define EPOLLMSG EPOLLMSG
EPOLLERR = 0x008,
#define EPOLLERR EPOLLERR
EPOLLHUP = 0x010,
#define EPOLLHUP EPOLLHUP
EPOLLRDHUP = 0x2000,
#define EPOLLRDHUP EPOLLRDHUP
EPOLLWAKEUP = 1u << 29,
#define EPOLLWAKEUP EPOLLWAKEUP
EPOLLONESHOT = 1u << 30,
#define EPOLLONESHOT EPOLLONESHOT
EPOLLET = 1u << 31
#define EPOLLET EPOLLET
};
(3)epoll_wait();
参数events是分配好的epoll_event结构体数组； epoll将会把发生的事件复制到events数组中(events不可以是空指针，内核只负责把数据复制到) 参数timeout 是超时时间(毫秒，0表示立即返回，-1表示永久阻塞)； 如果函数调用成功，返回对应IO上已经准备好的文件描述符数目；如果返回0，表示已超时；如果返回值小于0，表示函数失败。
Linuxc/c++服务器开发高阶视频学习资料后台私信【架构】获取
3.epoll mode
epoll的使用也很方便，基本都会用到以下模型，取自linux帮助手册：
/*Example for suggested usageWhile the usage of epoll when employed as a level-triggered interface does have the same semantics as poll(2), the edge-triggered usage requires moreclarification to avoid stalls in the application event loop. In this example, listener is a nonblocking socket on which listen(2) has been called. Thefunction do_use_fd() uses the new ready file descriptor until EAGAIN is returned by either read(2) or write(2). An event-driven state machine applica‐tion should, after having received EAGAIN, record its current state so that at the next call to do_use_fd() it will continue to read(2) or write(2) fromwhere it stopped before.*/ #define MAX_EVENTS 10struct epoll_event ev, events[MAX_EVENTS];int listen_sock, conn_sock, nfds, epollfd; /* Code to set up listening socket, 'listen_sock', (socket(), bind(), listen()) omitted */ static Epoll_Case(){ epollfd = epoll_create1(0); if (epollfd == -1) { perror("epoll_create1"); exit(EXIT_FAILURE); } ev.events = EPOLLIN; ev.data.fd = listen_sock; if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) { perror("epoll_ctl: listen_sock"); exit(EXIT_FAILURE); } for (;;) { nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1); if (nfds == -1) { perror("epoll_wait"); exit(EXIT_FAILURE); } for (n = 0; n < nfds; ++n) { if (events[n].data.fd == listen_sock) { conn_sock = accept(listen_sock, (struct sockaddr *) &local, &addrlen); if (conn_sock == -1) { perror("accept"); exit(EXIT_FAILURE); } setnonblocking(conn_sock); ev.events = EPOLLIN | EPOLLET; ev.data.fd = conn_sock; if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock, &ev) == -1) { perror("epoll_ctl: conn_sock"); exit(EXIT_FAILURE); } } else { do_use_fd(events[n].data.fd); } } }} /* When used as an edge-triggered interface, for performance reasons, it is possible to add the file descriptor inside the epoll interface (EPOLL_CTL_ADD)once by specifying (EPOLLIN|EPOLLOUT). This allows you to avoid continuously switching between EPOLLIN and EPOLLOUT calling epoll_ctl(2) withEPOLL_CTL_MOD.*/ 下面给出一个epoll 服务器的简单例子,参考了网上不少方式，自己写了一个，算不上原创，把BIT_TEST部分注释打开，可以忽略basetype.h,可以编译通过。创建socket的地方可以自己优化省略，我实现的时候觉得这种方式比较容易看清楚socket的获取方式。
#include #include #include #include #include #include #include #include #include #include #include #include #include #include "basetype.h" static int g_Main_Epoll_Fd = -1;#define MAX_EPOLL_EVENT_COUNT 64#define MAX_LISTEN_NUM 10#define MAX_BUFF_LEN 512 /*#define BIT_TEST(a, b) ((a) & (b))#define BIT_RESET(a, b) ((a) ~= (b))#define BIT_SET(a, b) ((a) |= (b))#define BIT_MATCH(a,b) ((a)&(b) = (b))#define BIT_COMPARE(a, b, c) ((a)&(b) == (c))*/ static void print_socket_info(struct addrinfo *ai){ char ipstr[INET6_ADDRSTRLEN]; uint16_t port; void *addr = NULL; char *ipver = NULL; struct sockaddr_in *ipv4 = NULL; struct sockaddr_in6 *ipv6 = NULL; assert(NULL != ai); if (ai->ai_family == AF_INET) { // IPv4 ipv4 = (struct sockaddr_in *)ai->ai_addr; addr = &(ipv4->sin_addr); ipver = "IPv4"; port =ntohs(((struct sockaddr_in*)ai->ai_addr)->sin_port); } else { // IPv6 ipv6 = (struct sockaddr_in6 *)ai->ai_addr; addr = &(ipv6->sin6_addr); ipver = "IPv6"; port =ntohs(((struct sockaddr_in6*)ai->ai_addr)->sin6_port); } // convert the IP to a string and print it: (void)inet_ntop(ai->ai_family, addr, ipstr, sizeof ipstr); printf(" server initing... AF: %s IP: %s,PORT: %u", ipver, ipstr,port); return ;} static int SetSocketNoblocking(const int sockfd){ int flags = 0; int iret = 0; flags = fcntl (sockfd, F_GETFL, 0); if (flags == -1) { perror ("fcntl"); return -1; } flags |= O_NONBLOCK; iret = fcntl (sockfd, F_SETFL, flags); if (iret == -1) { perror ("fcntl"); return -1; } return 0;} static int Epoll_Control(const int sockfd, const int oper, const int events){ struct epoll_event ep_event; int iret = 0; memset(&ep_event, 0, sizeof(ep_event)); ep_event.events = events; ep_event.data.fd = sockfd; iret = epoll_ctl(g_Main_Epoll_Fd, oper, sockfd, &ep_event); if (0 > iret) { perror("epoll_ctl error."); printf("epoll_ctl error opt:%d", oper); return -1; } return 0;} static int CreateServerScoket(const char *host, const char *port){ struct addrinfo hints; struct addrinfo*ailist= NULL; struct addrinfo *ai= NULL; int iret; int sockfd = 0; int sockoptval = 1; memset(&hints, 0, sizeof(hints)); hints.ai_family = AF_UNSPEC; // AF_INET 或 AF_INET6 hints.ai_socktype = SOCK_STREAM; hints.ai_flags = AI_PASSIVE; /* All interfaces */ iret = getaddrinfo(host, port, &hints, &ailist); if (0 != iret) { fprintf(stderr, "getaddrinfo: %s", gai_strerror(iret)); return -1; } for(ai = ailist;ai != NULL; ai = ai->ai_next) { sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol); if (0 > sockfd) { continue; } /* set reuse addr */ iret = setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &sockoptval, sizeof(sockoptval)); if (0 > iret) { perror("setsockopt error"); freeaddrinfo(ailist); return -1; } iret = bind(sockfd, ai->ai_addr, ai->ai_addrlen);/*sizeof(struct sockaddr)*/ if (0 == iret) { print_socket_info(ai); break; } else { close(sockfd); } } if (NULL == ai) { fprintf(stderr, "get server socket error."); return -1; } freeaddrinfo(ailist); /* set no-block mode */ iret = SetSocketNoblocking(sockfd); if (0 != iret) { return -1; } /* listen socket */ iret = listen(sockfd, MAX_LISTEN_NUM); if (0 > iret) { perror("listen socket error."); return -1; } printf("server socket init success. listenning..."); return sockfd;} static void HandleAccept(const int listen_scok, int Event){ struct sockaddr_in addr; socklen_t len = sizeof(addr); int client_sock = -1; if (BIT_TEST(EPOLLIN, Event)) { client_sock = accept(listen_scok, (struct sockaddr *)&addr, &len); if(client_sock < 0 ) { perror("accept infd error"); return; } (void)Epoll_Control(client_sock, EPOLL_CTL_ADD, EPOLLIN); } return ;} static void ProcRecvMsg(int sockfd){ ssize_t recvlen = 0; char recvBuf[MAX_BUFF_LEN]; //read ev ready; recvlen = recv(sockfd, recvBuf, sizeof(recvBuf), 0); if(recvlen < 0) { perror("recv error."); return ; } else if(recvlen == 0) { printf("client quit"); (void)Epoll_Control(sockfd, EPOLL_CTL_DEL, 0); close(sockfd); } else { (void)Epoll_Control(sockfd, EPOLL_CTL_MOD, EPOLLOUT); printf("recv msg fprom client:msg#:%s",recvBuf); } return ;} static void SendMsg2Client(const int sockfd){ ssize_t sendlen = 0; char sendBuf[MAX_BUFF_LEN]; int event = 0; sprintf(sendBuf, "HTTP/1.0 200 OKHello Epoll! [client_fd:%d]
", sockfd); int sendsize = send(sockfd, sendBuf, strlen(sendBuf)+1, 0); if(sendsize <= 0) { perror("send error."); (void)Epoll_Control(sockfd, EPOLL_CTL_DEL, 0); close(sockfd); } else { printf("Server reply msg ok! data: %s", sendBuf); event = EPOLLIN | EPOLLERR | EPOLLHUP; (void)Epoll_Control(sockfd, EPOLL_CTL_MOD, event); } return ;} int main(int argc, char *argv[]){ int listenfd =0; int epfd = 0; int iret = 0; int event = 0; struct epoll_event ep_events[MAX_EPOLL_EVENT_COUNT]; int ev_num = 0; int in_sockfd = 0; int loop = 0; if (3 > argc) { printf("Usage: %s [ip_addr] [port]",argv[0]); return -1; } listenfd = CreateServerScoket(argv[1], argv[2]); if (0 > listenfd) { return -1; } epfd = epoll_create(1); if (-1 == epfd) { perror("create epoll error."); return -1; } else { g_Main_Epoll_Fd = epfd; } event = EPOLLIN; iret = Epoll_Control(listenfd, EPOLL_CTL_ADD, event); if (0 != iret) { return -1; } /* proc epoll event regined */ printf("server init success, epoll wait now."); for(;;) { memset(ep_events, 0, sizeof(ep_events)); ev_num = epoll_wait(g_Main_Epoll_Fd, ep_events, MAX_EPOLL_EVENT_COUNT, -1); switch (ev_num) { case 0: { printf("epoll_wait timeout."); break; } case -1: { perror("epoll_wait error."); break; } default: { for (loop = 0; loop < ev_num; loop++) { in_sockfd = ep_events[loop].data.fd; event = ep_events[loop].events; if (in_sockfd == listenfd) { HandleAccept(in_sockfd, event); } else { if (BIT_TEST(EPOLLIN, event)) { /* have data to read */ ProcRecvMsg(in_sockfd); } else if (BIT_TEST(EPOLLOUT, event)) { SendMsg2Client(in_sockfd); } } } break; } } } return 0;}结果如下，客户端任意都可以：注意，运行时需要手动输入服务器主机名及端口号。
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