最简单的 socket 套接字编程(2) -- poll() 和 epoll()
最简单的 socket 套接字编程(2) – poll() 和 epoll()
本文主要介绍了使用poll()和epoll()在UNIX环境下socket网络编程的主要步骤，实现
了一个简单的 服务器和客户端代码实例，实现了一个网络服务，该服务接受一个字符串的命令，执行该命
令，并且把结 果返回给客户端。
关于socket网络编程的基本概念以及多进程、多线程的网络服务器的原理和实例，参考 最简单的socket套接字编程。
关于poll()和epoll()的介绍和用法，参考
一步步理解Linux之IO（2）–高级IO
Client
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define BUFLEN 256
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[BUFLEN];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
if ((server = gethostbyname(argv[1])) == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
while (1) {
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
error("ERROR opening socket");
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
printf(">>> ");
bzero(buffer, BUFLEN);
fgets(buffer, BUFLEN, stdin);
if((n = send(sockfd, buffer, strlen(buffer), 0)) <= 0)
error("ERROR writing to socket");
bzero(buffer, BUFLEN);
while ((n = recv(sockfd, buffer, BUFLEN, 0)) > 0) {
printf("%s",buffer);
}
}
return 0;
}
poll()实现的server
/* A simple server to run system commands use poll */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <poll.h>
#include <fcntl.h>
#define PORTNO 4444
#define BACKLOG 10
#define BUFLEN 256
#define MAXCONN 100
#define TRUE 1
#define FALSE 0
void error(const char *msg) {
perror(msg);
}
/*
* function really do the service
* run cmd geted from client and return the output to client
*/
void serve(struct pollfd *pfd) {
int n;
char buffer[BUFLEN];
FILE *fp;
bzero(buffer, BUFLEN);
printf("in serve ,fd=%d\n", pfd->fd);
if (pfd->revents & POLLIN) { /* read */
if ((n = read(pfd->fd, buffer, BUFLEN)) < 0)
printf("ERROR reading from socket : %d", n);
printf("CMD : %s\n",buffer);
if ((fp = popen(buffer, "r")) == NULL)
error("ERROR when popen");
while (fgets(buffer, BUFLEN, fp) != NULL) {
if (send(pfd->fd, buffer, BUFLEN, 0) == -1)
error("send ERROR");
}
printf("serve end, closing %d\n", pfd->fd);
close(pfd->fd);
pfd->fd = -1;
pclose(fp);
}
}
/*
* Init listen socket and bind it to addr, return the listen socket
*/
int init_server() {
int sockfd;
struct sockaddr_in serv_addr;
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
error("ERROR opening socket");
exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(PORTNO);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
error("ERROR on binding");
exit(1);
}
return sockfd;
}
/*
* set fd nonblocking, success return 0, fail return -1
*/
int setnonblocking(int fd) {
if (fd > 0) {
int flags = fcntl(fd, F_GETFL, 0);
flags = flags|O_NONBLOCK;
if (fcntl(fd, F_SETFL, flags) == 0) {
printf("setnonblocking success!\n");
return 0;
}
}
return -1;
}
void printfd(struct pollfd array[], int n) {
int i;
printf("array = ");
for(i = 0; i < n; i++)
printf("[%d]:%d ", i, array[i].fd);
printf("\n");
}
/*
* Use poll() to serve for every connection
*/
int main(int argc, char *argv[]) {
int endserver = FALSE;
int listen_sock, conn_sock, pos, i, j;
struct sockaddr_in cli_addr;
socklen_t clilen = sizeof(cli_addr);
/* INIT pollfd structures */
struct pollfd allfds[MAXCONN];
printf("sizeof(allfds)=%d\n", (int)sizeof(allfds));
memset(allfds, 0, sizeof(allfds));
int nfds = 0; /* number of fds in allfds */
int currentsize; /* current size of allfds */
int poll_result;
/* init listen socket, bind, listen */
listen_sock = init_server();
setnonblocking(listen_sock);
listen(listen_sock, BACKLOG);
/* add listen_socket to allfds array */
allfds[0].fd = listen_sock;
allfds[0].events = POLLIN;
nfds++;
while (endserver == FALSE) {
printfd(allfds, nfds);
printf("nfds=%d\n", nfds);
/* wait for events on sockets, timeout = -1 means waite forever */
poll_result = poll(allfds, nfds, -1);
if (poll_result == -1) {
error("poll ERROR");
break;
} else if (poll_result == 0) {
printf("poll round timeout, enther another poll...\n");
continue;
}
/*******************************************************************/
/* One or more descriptors are readable */
/*******************************************************************/
currentsize = nfds;
printf("correntsize=%d\n", currentsize);
for (pos = 0; pos < currentsize; pos++) {
if (allfds[pos].revents & POLLIN &&
allfds[pos].fd == listen_sock) { /* listen socket */
printf("event on listen sock\n");
/* Accept all incomming connections */
do {
printf("listen_sock=%d\n", listen_sock);
conn_sock = accept(listen_sock,
(struct sockaddr *)&cli_addr, &clilen);
if (conn_sock < 0)
continue;
setnonblocking(conn_sock);
if (nfds >= MAXCONN) {
error("nfds >= MAXCONN");
break;
}
allfds[nfds].fd = conn_sock;
allfds[nfds].events = POLLIN;
nfds++;
} while(conn_sock != -1);
/* regular socket */
} else {
serve(&allfds[pos]);
}
/* comparess allfds, delete the items which fd = -1 */
for (i = 0; i < nfds; i++) {
if (allfds[i].fd == -1) {
for (j = i; j < nfds; j++) {
allfds[j] = allfds[j+1];
}
nfds--;
i--;
}
}
}
}
/* end server */
for (i = 0; i < nfds; i++) {
if (allfds[i].fd >= 0)
close(allfds[i].fd);
}
return 0;
}
epoll()实现的server
/* A simple server to run system commands use poll */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <fcntl.h>
#define PORTNO 4444
#define BACKLOG 10
#define BUFLEN 256
#define MAXCONN 100
#define TRUE 1
#define FALSE 0
void error(const char *msg) {
perror(msg);
}
/*
* function really do the service
* run cmd geted from client and return the output to client
*/
void serve(int fd) {
int n;
char buffer[BUFLEN];
FILE *fp;
bzero(buffer, BUFLEN);
printf("in serve ,fd=%d\n", fd);
if ((n = read(fd, buffer, BUFLEN)) < 0)
printf("ERROR reading from socket : %d", n);
printf("CMD : %s\n",buffer);
if ((fp = popen(buffer, "r")) == NULL)
error("ERROR when popen");
while (fgets(buffer, BUFLEN, fp) != NULL) {
if (send(fd, buffer, BUFLEN, 0) == -1)
error("send ERROR");
}
printf("serve end, closing %d\n", fd);
pclose(fp);
}
/*
* Init listen socket and bind it to addr, return the listen socket
*/
int init_server() {
int sockfd;
struct sockaddr_in serv_addr;
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
error("ERROR opening socket");
exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(PORTNO);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
error("ERROR on binding");
exit(1);
}
return sockfd;
}
/*
* set fd nonblocking, success return 0, fail return -1
*/
int setnonblocking(int fd) {
if (fd > 0) {
int flags = fcntl(fd, F_GETFL, 0);
flags = flags|O_NONBLOCK;
if (fcntl(fd, F_SETFL, flags) == 0) {
printf("setnonblocking success!\n");
return 0;
}
}
return -1;
}
/*
* Use poll() to serve for every connection
*/
int main(int argc, char *argv[]) {
int endserver = FALSE;
int listen_sock, conn_sock, n;
struct sockaddr_in cli_addr;
socklen_t clilen = sizeof(cli_addr);
/* INIT pollfd structures */
struct epoll_event ev, events[MAXCONN];
int nfds;
int epollfd = epoll_create(10);
if (epollfd == -1) {
printf("epoll_create error\n");
exit(1);
}
/* init listen socket, bind, listen */
listen_sock = init_server();
setnonblocking(listen_sock);
listen(listen_sock, BACKLOG);
/* register listen_sock to epollfd */
ev.events = EPOLLIN;
ev.data.fd = listen_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) {
printf("ERROR: epoll_ctl\n");
exit(1);
}
while (endserver == FALSE) {
nfds = epoll_wait(epollfd, events, MAXCONN, -1);
if (nfds == -1) {
printf("epoll_wait ERROR\n");
exit(1);
}
for (n = 0; n < nfds; n++) {
if (events[n].data.fd == listen_sock) { /* listen socket */
do {
printf("listen_sock=%d\n", listen_sock);
conn_sock = accept(listen_sock,
(struct sockaddr *)&cli_addr, &clilen);
if (conn_sock < 0)
continue;
setnonblocking(conn_sock);
ev.events = EPOLLIN|EPOLLET;
ev.data.fd = conn_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock, &ev)
== -1) {
printf("epoll_ctl for conn_sock ERROR\n");
exit(1);
}
} while(conn_sock != -1);
} else { /* regular connection */
serve(events[n].data.fd);
ev.events = EPOLLIN|EPOLLET;
ev.data.fd = conn_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_DEL, events[n].data.fd, &ev)
== -1) {
printf("epoll_ctl DEL ERROR\n");
exit(1);
}
close(events[n].data.fd);
}
}
}
return 0;
}
参考资料：
- 《UNIX环境高级编程》
- Using poll() instead of select()
- Man pages