网络编程--IO模型示例

IO模型在Richard Stevens的《UNIX网络编程，第一卷》（程序猿必备！）一书中有非常详尽的描述，以下简要介绍，并给出代码示例。

另外比较好的总结性blog，推荐：
使用异步 I/O 大大提高应用程序的性能
IO - 同步，异步，阻塞，非阻塞 （亡羊补牢篇）

常见网络IO模型：阻塞式IO、无阻塞式IO、IO复用、异步IO、信号驱动

阻塞式IO：
在一个进程发出IO请求后，进入阻塞状态，直到内核返回数据，才重新运行，如图：

代码
sever端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>int main(){int sockfd, new_fd;int sin_size, numbytes;struct sockaddr_in addr, cliaddr;//创建socketif((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){perror("createSocket");return -1;}//初始化socket结构memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_port = htons(7092);addr.sin_addr.s_addr = htonl(INADDR_ANY);//绑定套接口if(bind(sockfd,(struct sockaddr *)&addr,sizeof(struct sockaddr))==-1){perror("bind");return -1;}//创建监听套接口if(listen(sockfd,10)==-1){perror("listen");return -1;}printf("server is running!\n");char buff[1024];//等待连接while(1) {sin_size = sizeof(struct sockaddr_in);//接受连接if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1){perror("accept");return -1;}//生成一个子进程来完成和客户端的会话，父进程继续监听if(!fork()){//读取客户端发来的信息memset(buff,0,sizeof(buff));if((numbytes = recv(new_fd,buff,sizeof(buff),0))==-1){perror("recv");return -1;}printf("buff=%s\n",buff);//将从客户端接收到的信息再发回客户端if(send(new_fd,buff,strlen(buff),0)==-1){perror("send");}close(new_fd);return 0;}//父进程关闭new_fdclose(new_fd);}close(sockfd);}

client端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>int main(int argc,char *argv[]){if(argc!=3){printf("%s: input IP & port\n",argv[0]);return 1;}int sockfd,numbytes;char buf[100] = "hello world";struct hostent *he;struct sockaddr_in their_addr;//将基本名字和地址转换he = gethostbyname(argv[1]);//建立一个TCP套接口if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}//初始化结构体their_addr.sin_family = AF_INET;their_addr.sin_port = htons(atoi(argv[2]));their_addr.sin_addr = *((struct in_addr *)he->h_addr);bzero(&(their_addr.sin_zero),8);//和服务器建立连接if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){perror("connect");exit(1);}//向服务器发送字符串if(send(sockfd,buf,strlen(buf),0)==-1){perror("send");exit(1);}memset(buf,0,sizeof(buf));//接受从服务器返回的信息if((numbytes = recv(sockfd,buf,100,0))==-1){perror("recv");exit(1);}close(sockfd);return 0;}

运行：
$ ./bin/server
server is running!
buff=hello world
buff=hello world

$ ./bin/client 10.32.49.10 7092
$ ./bin/client 10.32.49.10 7092

无阻塞式IO：
在一个进程发出IO请求后，不阻塞，如果数据没有准备好，就直接返回错误码，如图：

可以通过fcntl控制socket描述符属性。
int flags;
flag=fcntl(sockfd,F_GETFL,0);
fcntl(sockfd,F_SETFL,flag|O_NONBLOCK)

非阻塞式I/O模型对4种I/O操作返回的错误
读操作：接收缓冲区无数据时返回EWOULDBLOCK
写操作：发送缓冲区无空间时返回EWOULDBLOCK；空间不够时部分拷贝，返回实际拷贝字节数
建立连接：启动3次握手，立刻返回错误EINPROGRESS；服务器客户端在同一主机上connect立即返回成功
接受连接：没有新连接返回EWOULDBLOCK

代码：
server端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>#include <fcntl.h>int main(){int sockfd, new_fd;int sin_size;struct sockaddr_in addr, cliaddr;//创建socketif((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){perror("createSocket");return -1;}//初始化socket结构memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_port = htons(7092);addr.sin_addr.s_addr = htonl(INADDR_ANY);//绑定套接口if(bind(sockfd,(struct sockaddr *)&addr,sizeof(struct sockaddr))==-1){perror("bind");return -1;}//创建监听套接口if(listen(sockfd,10)==-1){perror("listen");return -1;}printf("server is running!\n");char buff[1024];//等待连接while(1) {sin_size = sizeof(struct sockaddr_in);//接受连接if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1){perror("accept");return -1;}//生成一个子进程来完成和客户端的会话，父进程继续监听if(!fork()){//设置new_fd无阻塞属性int flags;if((flags=fcntl(new_fd, F_GETFL, 0))<0)              {            perror("fcntl F_GETFL");              }        flags |= O_NONBLOCK;        if(fcntl(new_fd, F_SETFL,flags)<0)              {            perror("fcntl F_SETFL");  }//读取客户端发来的信息memset(buff,0,sizeof(buff));while(1){if((recv(new_fd,buff,sizeof(buff),0)) < 0){if(errno==EWOULDBLOCK){perror("recv error, wait....");sleep(1);continue;}}else{printf("buff=%s\n",buff);}break;}//发送数据while(1){if(send(new_fd,buff,strlen(buff),0) < 0){if(errno==EWOULDBLOCK){perror("send error, wait....");sleep(1);continue;}}else{printf("buff=%s\n",buff);}break;}close(new_fd);return 0;}//父进程关闭new_fdclose(new_fd);}close(sockfd);}

client端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>int main(int argc,char *argv[]){if(argc!=3){printf("%s: input IP & port\n",argv[0]);return 1;}int sockfd,numbytes;char buf[100] = "hello world";struct hostent *he;struct sockaddr_in their_addr;//将基本名字和地址转换he = gethostbyname(argv[1]);//建立一个TCP套接口if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}//初始化结构体their_addr.sin_family = AF_INET;their_addr.sin_port = htons(atoi(argv[2]));their_addr.sin_addr = *((struct in_addr *)he->h_addr);bzero(&(their_addr.sin_zero),8);//和服务器建立连接if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){perror("connect");exit(1);}sleep(5);//向服务器发送字符串if(send(sockfd,buf,strlen(buf),0)==-1){perror("send");exit(1);}memset(buf,0,sizeof(buf));sleep(5);//接受从服务器返回的信息if((numbytes = recv(sockfd,buf,100,0))==-1){perror("recv");exit(1);}close(sockfd);return 0;}

运行：
$ ./bin/server
server is running!
recv error, wait....: Resource temporarily unavailable
recv error, wait....: Resource temporarily unavailable
recv error, wait....: Resource temporarily unavailable
recv error, wait....: Resource temporarily unavailable
recv error, wait....: Resource temporarily unavailable
buff=hello world
buff=hello world

$ ./bin/client 10.32.49.10 7092

IO复用：
IO复用阻塞在select、poll或epoll这样的系统调用上，通过这种方式，在不使用多线程的前提下，单个进程可以同时处理多个网络连接的IO。如图：

代码
sever端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>#include <fcntl.h>#include <netdb.h>#include <sys/epoll.h>#define MAXEVENT 1024int create_server_socket(int& sockfd){struct sockaddr_in addr;//创建socketif((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){perror("createSocket");return -1;}//初始化socket结构memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_port = htons(7092);addr.sin_addr.s_addr = htonl(INADDR_ANY);//绑定套接口if(bind(sockfd,(struct sockaddr *)&addr,sizeof(struct sockaddr))==-1){perror("bind");return -1;}//创建监听套接口if(listen(sockfd,10)==-1){perror("listen");return -1;}return 0;}int set_socket_non_blocking(int fd){int flags, s;flags = fcntl (fd, F_GETFL, 0);if (flags == -1){perror ("fcntl F_GETFL failed");return -1;}flags |= O_NONBLOCK;s = fcntl (fd, F_SETFL, flags);if (s == -1){perror ("fcntl F_SETFL failed");return -1;}return 0;}int main(){int sockfd, efd;struct epoll_event event;struct epoll_event *events;int s;if(create_server_socket(sockfd) != 0){perror("create server sock failed\n");return 1;}set_socket_non_blocking(sockfd);printf("server is running!\n");//创建一个epoll的句柄//int epoll_create(int size)  //Since Linux 2.6.8, the size argument is unused. (The kernel dynamically sizes the required data structures without needing this initial hint.)efd = epoll_create(MAXEVENT);if (efd == -1){perror ("epoll_create");abort ();}//注册新事件到epoll efdevent.data.fd = sockfd;event.events = EPOLLIN | EPOLLET;s = epoll_ctl(efd, EPOLL_CTL_ADD, sockfd, &event);if (s == -1){perror ("epoll_ctl EPOLL_CTL_ADD failed");abort ();}events = (epoll_event*)calloc(MAXEVENT, sizeof(event));while (1){int n, i;n = epoll_wait(efd, events, MAXEVENT, -1);for (i = 0; i < n; i++){    //fd error      if ((events[i].events & EPOLLERR) ||              (events[i].events & EPOLLHUP) ||              (!(events[i].events & EPOLLIN)))        {perror("epoll error\n");close (events[i].data.fd);continue;}//新连接      else if (sockfd == events[i].data.fd)       {while (1){struct sockaddr in_addr;socklen_t in_len;int infd;char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];//接受连接in_len = sizeof(in_addr);infd = accept(sockfd, &in_addr, &in_len);if (infd == -1){if ((errno == EAGAIN) ||  (errno == EWOULDBLOCK)){//已接受所有连接      break;    }else{perror ("accept");break;}}s = getnameinfo (&in_addr, in_len,               hbuf, sizeof hbuf,               sbuf, sizeof sbuf,               NI_NUMERICHOST | NI_NUMERICSERV);if (s == 0){  printf("Accepted connection on descriptor %d "         "(host=%s, port=%s)\n", infd, hbuf, sbuf);}/* 设置新接受的socket连接无阻塞*/s = set_socket_non_blocking (infd);if (s == -1){return 1;}//注册新事件到epollevent.data.fd = infd;event.events = EPOLLIN | EPOLLET;s = epoll_ctl(efd, EPOLL_CTL_ADD, infd, &event);if (s == -1){  perror ("epoll_ctl");  return 1;}}continue;            }            //数据可读          else            {              int done = 0;              while (1)              {                  ssize_t count;                  char buf[512];                  count = read(events[i].data.fd, buf, sizeof(buf));                  if(count == -1)                  {                      //数据读完                      if (errno != EAGAIN)                      {                          perror ("read");                          done = 1;                      }                      break;                  }                  else if(count == 0)                  {                      /* End of file. The remote has closed the                         connection. */                      done = 1;                      break;                   }                  printf("recv: %s\n", buf);                }              if (done)              {                  printf ("Closed connection on descriptor %d\n", events[i].data.fd);                  close (events[i].data.fd);              }            }        }    }  free (events);  close(sockfd);  return 0;}

client端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>int main(int argc,char *argv[]){if(argc!=3){printf("%s: input IP & port\n",argv[0]);return 1;}int sockfd,numbytes;char buf[100] = "hello world";struct hostent *he;struct sockaddr_in their_addr;//将基本名字和地址转换he = gethostbyname(argv[1]);//建立一个TCP套接口if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}//初始化结构体their_addr.sin_family = AF_INET;their_addr.sin_port = htons(atoi(argv[2]));their_addr.sin_addr = *((struct in_addr *)he->h_addr);bzero(&(their_addr.sin_zero),8);//和服务器建立连接if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){perror("connect");exit(1);}//向服务器发送字符串while(1){if(send(sockfd,buf,strlen(buf),0)==-1){perror("send");exit(1);}sleep(2);}memset(buf,0,sizeof(buf));close(sockfd);return 0;}

运行：
$ ./bin/server    
server is running!
Accepted connection on descriptor 5 (host=10.32.49.10, port=39001)
recv: hello world
recv: hello world
recv: hello world
recv: hello world

./bin/client 10.32.49.10 7092

异步IO：
在一个进程发出IO请求后直接返回，内核在整个操作（包括将数据复制到进程缓冲区）完成后通知进程，如图：

代码
server端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>#include <fcntl.h>#include <aio.h>#include <pthread.h>#define BUF_SIZE 1024void aio_completion_handler(sigval_t sigval);void setup_io(int fd, aiocb& my_aiocb){//初始化AIO请求bzero( (char *)&my_aiocb, sizeof(struct aiocb) );my_aiocb.aio_fildes = fd;my_aiocb.aio_buf = malloc(BUF_SIZE+1);my_aiocb.aio_nbytes = BUF_SIZE;my_aiocb.aio_offset = 0;//设置线程回调函数my_aiocb.aio_sigevent.sigev_notify = SIGEV_THREAD;my_aiocb.aio_sigevent.sigev_notify_function = aio_completion_handler;my_aiocb.aio_sigevent.sigev_notify_attributes = NULL;my_aiocb.aio_sigevent.sigev_value.sival_ptr = &my_aiocb;}//回调函数void aio_completion_handler(sigval_t sigval){struct aiocb *req;int ret;req = (struct aiocb *)sigval.sival_ptr;if (aio_error(req) == 0) {if((ret = aio_return(req)) > 0){printf("Thread id %u recv:%s\n", (unsigned int)pthread_self(), (char*)req->aio_buf);}}char* buf = (char*)req->aio_buf;if(send(req->aio_fildes, buf, strlen(buf), 0) == -1){perror("send");return;}close(req->aio_fildes);return;}int main(){int sockfd;int sin_size;struct sockaddr_in addr, cliaddr;//创建socketif((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){perror("createSocket");return -1;}//初始化socket结构memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_port = htons(7092);addr.sin_addr.s_addr = htonl(INADDR_ANY);//绑定套接口if(bind(sockfd,(struct sockaddr *)&addr,sizeof(struct sockaddr))==-1){perror("bind");return -1;}//创建监听套接口if(listen(sockfd,10)==-1){perror("listen");return -1;}printf("server is running!\n");//等待连接while(1) {int new_fd;  struct aiocb my_aiocb;sin_size = sizeof(struct sockaddr_in);//接受连接if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1){perror("accept");return -1;}printf("Thread id %u accept connect, fd: %d\n", (unsigned int)pthread_self(), new_fd);setup_io(new_fd, my_aiocb);aio_read(&my_aiocb);}close(sockfd);}

client端：

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <unistd.h>int main(int argc,char *argv[]){if(argc!=3){printf("%s: input IP & port\n",argv[0]);return 1;}int sockfd,numbytes;char buf[100] = "hello world";struct hostent *he;struct sockaddr_in their_addr;//将基本名字和地址转换he = gethostbyname(argv[1]);//建立一个TCP套接口if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}//初始化结构体their_addr.sin_family = AF_INET;their_addr.sin_port = htons(atoi(argv[2]));their_addr.sin_addr = *((struct in_addr *)he->h_addr);bzero(&(their_addr.sin_zero),8);//和服务器建立连接if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){perror("connect");exit(1);}//向服务器发送字符串if(send(sockfd,buf,strlen(buf),0)==-1){perror("send");exit(1);}         //接收数据if((numbytes = recv(sockfd, buf, 100, 0)) == -1){perror("recv");return 1;}printf("recv: %s\n", buf);close(sockfd);return 0;}

运行：
$ ./bin/server
server is running!
Thread id 2505492000 accept connect, fd: 4
Thread id 1084246368 recv:hello world
（注意：线程ID不一样）

$ ./bin/client 10.32.49.10 7092
recv: hello world


信号驱动IO：
使用信号驱动I/O时，当网络套接字可读后，内核通过发送SIGIO信号通知应用进程，于是应用可以开始读取数据。如图：

为了让套接字描述符可以工作于信号驱动I/O模式，应用进程必须完成如下三步设置：
1.注册SIGIO信号处理程序。(安装信号处理器)
2.使用fcntl的F_SETOWN命令，设置套接字所有者。（设置套接字的所有者）
3.使用fcntl的F_SETFL命令，置O_ASYNC标志，允许套接字信号驱动I/O。（允许这个套接字进行信号输入输出）
注意，必须保证在设置套接字所有者之前，向系统注册信号处理程序，否则就有可能在fcntl调用后，信号处理程序注册前内核向应用交付SIGIO信号，导致应用丢失此信号。

在UDP编程中使用信号驱动I/O，此时SIGIO信号产生于下面两种情况：
套接字收到一个数据报。
套接字上发生了异步错误。
因此，当应用因为收到一个UDP数据报而产生的SIGIO时，要么可以调用recvfrom读取该数据报，要么得到一个异步错误。
对于TCP编程，信号驱动I/O就没有太大意义了，因为对于流式套接字而言，有很多情况都可以导致SIGIO产生，而应用又无法区分是什么具体情况导致该信号产生的
信号驱动IO模型在网络编程中极少使用，这里不写例子了，有兴趣的同学可以参考：http://blog.csdn.net/yskcg/article/details/6021275

例子源码打包下载：
http://download.csdn.net/detail/yfkiss/4288465

reference：
UNIX网络编程，第一卷
Linux下 fcntl 函数用法说明
Linux Epoll详解
使用异步 I/O 大大提高应用程序的性能
信号驱动IO