服务器四：多进程epoll

 #include <fcntl.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <signal.h>
 #include <fcntl.h>
 #include <sys/wait.h>
 #include <sys/epoll.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <errno.h>
 #include <string.h>
 #include <vector>
 #include <algorithm>
 #include <iostream>
 #include <pthread.h>
 #include <sys/types.h>//包含pthread_self
 #include <unistd.h>//包含syscall
 #include <sys/syscall.h>

 #define gettid() syscall(__NR_gettid)

 typedef std::vector<struct epoll_event> EventList;

 #define ERR_EXIT(m) \
     do \
 { \
     perror(m); \
     exit(EXIT_FAILURE); \
     } while()

 int main(void)
 {
     //CP是全双工的信道, 可以看作两条单工信道, TCP连接两端的两个端点各负责一条. 当对端调用close时, 虽然本意是关闭整个两条信道,
     //但本端只是收到FIN包. 按照TCP协议的语义, 表示对端只是关闭了其所负责的那一条单工信道, 仍然可以继续接收数据. 也就是说, 因为TCP协议的限制,
     //一个端点无法获知对端的socket是调用了close还是shutdown.
     //对一个已经收到FIN包的socket调用read方法,
     //如果接收缓冲已空, 则返回0, 这就是常说的表示连接关闭. 但第一次对其调用write方法时, 如果发送缓冲没问题, 会返回正确写入(发送).
     //但发送的报文会导致对端发送RST报文, 因为对端的socket已经调用了close, 完全关闭, 既不发送, 也不接收数据. 所以,
     //第二次调用write方法(假设在收到RST之后), 会生成SIGPIPE信号, 导致进程退出.
     //为了避免进程退出, 可以捕获SIGPIPE信号, 或者忽略它, 给它设置SIG_IGN信号处理函数:
     //这样, 第二次调用write方法时, 会返回-1, 同时errno置为SIGPIPE. 程序便能知道对端已经关闭.
     signal(SIGPIPE, SIG_IGN);//防止进程退出
     //忽略SIGCHLD信号，这常用于并发服务器的性能的一个技巧
     //因为并发服务器常常fork很多子进程，子进程终结之后需要
     //服务器进程去wait清理资源。如果将此信号的处理方式设为
     //忽略，可让内核把僵尸子进程转交给init进程去处理，省去了
     //大量僵尸进程占用系统资源。(Linux Only)
     signal(SIGCHLD, SIG_IGN);

     int idlefd = open("/dev/null", O_RDONLY | O_CLOEXEC);
     int listenfd;
     //if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
     if ((listenfd = socket(PF_INET, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, IPPROTO_TCP)) < )
         ERR_EXIT("socket");

     struct sockaddr_in servaddr;
     memset(&servaddr, , sizeof(servaddr));
     servaddr.sin_family = AF_INET;
     servaddr.sin_port = htons();
     servaddr.sin_addr.s_addr = htonl(INADDR_ANY);

     int on = ;
     if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < )
         ERR_EXIT("setsockopt");

     if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < )
         ERR_EXIT("bind");
     if (listen(listenfd, SOMAXCONN) < )
         ERR_EXIT("listen");

     //create epoll object
     int epollfd;
     epollfd = epoll_create1(EPOLL_CLOEXEC);

     //add EPOLLIN event to epoll
     struct epoll_event event;
     event.data.fd = listenfd;
     event.events = EPOLLIN | EPOLLET;
     epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &event);

     EventList events();
     struct sockaddr_in peeraddr;
     socklen_t peerlen;
     int connfd;

     std::vector<int> clients;

     int nready;
     while ()
     {
         //return active event
         nready = epoll_wait(epollfd, &*events.begin(), static_cast<int>(events.size()), -);
         if (nready == -)
         {
             if (errno == EINTR)
                 continue;

             ERR_EXIT("epoll_wait");
         }
         if (nready == )    // nothing happended
             continue;

         //double capacity
         if ((size_t)nready == events.size())
             events.resize(events.size()*);

         //treat all active event
         for (int i = ; i < nready; ++i)
         {
             //如果是主socket的事件的话，则表示有新连接进入了，进行新连接的处理
             if (events[i].data.fd == listenfd)
             {
                 peerlen = sizeof(peeraddr);
                 connfd = ::accept4(listenfd, (struct sockaddr*)&peeraddr,
                                    &peerlen, SOCK_NONBLOCK | SOCK_CLOEXEC);

                 if (connfd == -)
                 {
                     //防止文件句柄超过最大数量
                     if (errno == EMFILE)
                     {
                         close(idlefd);
                         idlefd = accept(listenfd, NULL, NULL);
                         close(idlefd);
                         idlefd = open("/dev/null", O_RDONLY | O_CLOEXEC);
                         continue;
                     }
                     else
                         ERR_EXIT("accept4");
                 }

                 std::cout<<"ip="<<inet_ntoa(peeraddr.sin_addr)<<
                            " port="<<ntohs(peeraddr.sin_port)<<std::endl;

                 clients.push_back(connfd);

                 event.data.fd = connfd;
                 event.events = EPOLLIN | EPOLLET;
                 epoll_ctl(epollfd, EPOLL_CTL_ADD, connfd, &event);
             }
             else if (events[i].events & EPOLLIN)
             {
                 connfd = events[i].data.fd;
                 if (connfd < )
                     continue;

                 pid_t pid = fork();
                 if(pid == )
                 {
                     char recvBuf[] = {};
                     int ret = ;

                     while(true)
                     {
                         ret = read(connfd, recvBuf, );// 接受客户端消息
                         if(ret < )
                         {
                             break;// 这里表示读取数据出问题.
                             //由于是非阻塞的模式,所以当errno为EAGAIN时,表示当前缓冲区已无数据可//读在这里就当作是该次事件已处理过。
                             if(errno == EAGAIN)
                             {
                                 printf("EAGAIN\n");
                                 break;
                             }
                             else
                             {
                                 printf("read error! errno:%d\n", errno);
                                 ret = ;
                                 break;
                             }
                         }
                         else if(ret == )
                         {
                             // 这里表示对端的socket已正常关闭.
                             std::cout<<"client close"<<std::endl;
                             close(connfd);
                             event = events[i];
                             epoll_ctl(epollfd, EPOLL_CTL_DEL, connfd, &event);
                             clients.erase(std::remove(clients.begin(), clients.end(), connfd), clients.end());
                             break;
                         }
                         else
                         {
                             pid_t pid = getpid();
                             std::cout << pid << " recive data: " << recvBuf;
                             write(connfd, recvBuf, strlen(recvBuf));
                             break;
                         }
                     }
                 }
                 else
                 {
                     continue;
                 }
             }

         }
     }

     return ;
 }