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socket if((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! "); 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 ",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_fd close(new_fd); } close(sockfd); }
#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 ",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socket if((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! "); 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 ",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 ",buff); } break; } close(new_fd); return 0; } //父进程关闭new_fd close(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 ",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 1024 int create_server_socket(int& sockfd) { struct sockaddr_in addr; //创建socket if((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 "); return 1; } set_socket_non_blocking(sockfd); printf("server is running! "); //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 efd event.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 "); 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) ", 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epoll event.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 ", buf); } if (done) { printf ("Closed connection on descriptor %d ", 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 ",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 1024 void 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 ", (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socket if((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! "); //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 ", (unsigned int)pthread_self(), new_fd); setup_io(new_fd, my_aiocb); aio_read(&my_aiocb); } close(sockfd); }
client端:
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