知识点：三个多路并发模型（select 、poll 、epoll）
题目：以epoll模型，编写一个可供多个客户端访问的服务器程序。
实现代码：
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <sys/epoll.h>
#include <string.h>
#define SRV_PORT 60000
#define BUF_SIZE 1024
#define MAX_CONN 10000000 // 最大连接数
#define EVS_LEN 10 // epoll_wait()可保存的“收到数据”的fd的最大数目
void startServer()
{
int iRet;
char szSnd[BUF_SIZE];
char szRcv[BUF_SIZE];
char szBuf[BUF_SIZE];
int fd;
fd = socket(PF_INET, SOCK_STREAM, 0);
if (fd == -1) {
perror("fail socket");
return;
}
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);
addr.sin_port = htons(SRV_PORT);
iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr));
if (iRet == -1) {
perror("fail bind");
close(fd);
return;
}
listen(fd, MAX_CONN);
/*=========================================== epoll =======================================*/
int epfd = epoll_create(MAX_CONN); // function 1
struct epoll_event ev;
ev.events = EPOLLIN;
ev.data.fd = STDIN_FILENO;
epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev); // function 2
ev.events = EPOLLIN;
ev.data.fd = fd;
epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);
int clientFd;
struct sockaddr_in cliAddr;
socklen_t addrLen = sizeof(cliAddr);
struct epoll_event evs[EVS_LEN]; // 可容纳10个变化的fd
int cnt;
while(1) {
cnt = epoll_wait(epfd, evs, EVS_LEN, -1); // function 3
int i;
for (i = 0; i < cnt; i++) {
if (evs[i].data.fd == fd) {
/* new connect */
clientFd = accept(fd, (struct sockaddr*)&cliAddr, &addrLen);
ev.events = EPOLLIN;
ev.data.fd = clientFd;
epoll_ctl(epfd, EPOLL_CTL_ADD, clientFd, &ev);
printf("New connect from %s:%d\n", inet_ntoa(cliAddr.sin_addr), ntohs(cliAddr.sin_port));
write(clientFd, "Welcome...", 11);
}
else if (evs[i].data.fd == STDIN_FILENO) {
read(STDIN_FILENO, szSnd, BUF_SIZE);
printf("command not found\n");
}
else {
memset (szRcv, 0, BUF_SIZE);
iRet = read(evs[i].data.fd, szRcv, BUF_SIZE);
if (iRet == 0) {
/* 断开连接 */
printf("Disconnect fd:%d\n", evs[i].data.fd);
ev.data.fd = evs[i].data.fd;
epoll_ctl(epfd, EPOLL_CTL_DEL, evs[i].data.fd, NULL);
close(evs[i].data.fd);
}
else if (iRet < 0) {
perror("fail read");
return;
}
else {
memset(szBuf, 0, BUF_SIZE);
printf("Recv[%d]:%s\n", evs[i].data.fd, szRcv);
memcpy(szBuf, "I have received!", 17);
write(evs[i].data.fd, szBuf, strlen(szBuf));
}
}
}
}
close(fd);
return;
}
int main()
{
startServer();
return 0;
}
题目：以select模型，编写一个可供多个客户端访问的服务器程序。
实现代码：
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#define SRV_PORT 60000
#define BUF_SIZE 1024
#define MAX_CONN 10000
void startServer()
{
int iRet;
char szSnd[BUF_SIZE];
char szRcv[BUF_SIZE];
int fd;
fd = socket(PF_INET, SOCK_STREAM, 0);
if (fd == -1) {
perror("fail socket");
return;
}
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);
addr.sin_port = htons(SRV_PORT);
iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr));
if (iRet == -1) {
perror("fail bind");
close(fd);
return;
}
listen(fd, MAX_CONN);
/**************************************************** select *********************************************************/
fd_set fdset;
int i;
int maxfd = fd;
int clientFd;
int fdCnt = 0; // 当前连接的客户端数
int fdArr[MAX_CONN]; // 存放文件描述符fd的数组
struct sockaddr_in cliAddr;
socklen_t addrLen = sizeof(cliAddr);
while(1) {
/* select模型每次都要将“fd们”重新加入fdset，开销很大 */
FD_ZERO(&fdset);
FD_SET(STDIN_FILENO, &fdset);
FD_SET(fd, &fdset);
for (i = 0; i < fdCnt; i++) {
FD_SET(fdArr[i], &fdset); // 将用于和客户端通信的fd都加入fdset
}
select(maxfd + 1, &fdset, NULL, NULL, NULL);
if (FD_ISSET(fd, &fdset)) {
clientFd = accept(fd, (struct sockaddr*)&cliAddr, &addrLen);
if (fdCnt == MAX_CONN) {
printf("Connect over count\n");
write(clientFd, "please wait...", 15);
close(clientFd);
}
else {
printf("Connect from %s:%d success...\n", inet_ntoa(cliAddr.sin_addr), ntohs(cliAddr.sin_port));
write(clientFd, "Welcome...", 11);
fdArr[fdCnt++] = clientFd;
if (clientFd > maxfd) {
maxfd = clientFd; // 更新maxfd
}
}
}
if (FD_ISSET(STDIN_FILENO, &fdset)) {
memset(szSnd, 0, BUF_SIZE);
read(STDIN_FILENO, szSnd, 1024);
printf("command not found\n");
}
for (i = 0; i < fdCnt; i++) {
if (FD_ISSET(fdArr[i], &fdset)) {
memset(szRcv, 0, BUF_SIZE);
iRet = read(fdArr[i], szRcv, BUF_SIZE);
if (iRet > 0) {
printf("Recv[%d]:%s\n", fdArr[i], szRcv);
write(fdArr[i], "I received!", 12);
}
else if (iRet == 0) {
close(fdArr[i]);
printf("fd:%d disconnect...\n", fdArr[i]);
int j;
for(j = i; j < fdCnt - 1; j++) {
fdArr[j] = fdArr[j+1];
}
fdCnt--;
i--;
}
else {
perror("read fail");
return;
}
}
}
}
return;
}
int main()
{
startServer();
return 0;
}
小结：epoll模型的优点在于：①对于客户端的数量没有限制；②内核主动将“可读”的fd写入到struct epoll_events数组内，所以节省了poll模型和select模型的每次轮询整个fd集合的开销。