实现TCP并发服务器之四（poll函数）

poll函数类似于select函数，但是它的程序员接口不同，尽管它也可用于任何类型 文件描述符。与select不同，poll不为每个状态（可读，可写，异常状态）构造一个描述符集，而是构造一个pollfd结构数组，每个数组元素指定一个描述符编号以及对其所关心的状态。

struct pollfd {
int fd;				//file descriptor to check
short events;		//events of interest on fd
short revents;		//events that occured on fd
};

同样实现一个TCP服务器看看。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/poll.h>
#include<limits.h>

#define MAX_LISTEN 5
#define PORT 1987
#define IP "127.0.0.1"

#define MAX_POLL 100

//#define POLLRDNORM 0x0040

int main()
{
int conn_fd;
int sock_fd = socket(AF_INET,SOCK_STREAM,0);
if (sock_fd < 0) {
perror("create socket failed");
exit(1);
}

struct sockaddr_in addr_client;
int client_size = sizeof(struct sockaddr_in);

struct sockaddr_in addr_serv;
memset(&addr_serv, 0, sizeof(addr_serv));
addr_serv.sin_family = AF_INET;
addr_serv.sin_port = htons(PORT);
addr_serv.sin_addr.s_addr = inet_addr(IP);

if (bind(sock_fd,(struct sockaddr *)&addr_serv,sizeof(struct sockaddr_in)) < 0) {
perror("bind error");
exit(1);
}

if (listen(sock_fd,MAX_LISTEN) < 0) {
perror("listen failed");
exit(1);
}

//
int recv_num;
int send_num;
char recv_buf[100];
char send_buf[100];

//initial "poll" elements
int i, ready;
struct pollfd client[MAX_POLL];

client[0].fd = sock_fd;
client[0].events = POLLRDNORM;
for (i = 1;i < MAX_POLL; i ++) {
client[i].fd = -1;
}
int maxi = 0;

while (1) {

ready = poll(client, maxi + 1, 0);

//create new connection
if (client[0].revents & POLLRDNORM) {
conn_fd = accept(sock_fd, (struct sockaddr *)&addr_client, &client_size);
if (conn_fd < 0) {
perror("accept failed");
exit(1);
}

for (i = 1;i < MAX_POLL;i ++) {
if (client[i].fd < 0) {
client[i].fd = conn_fd;
break;
}
}
if (i == MAX_POLL) {
perror("too many clients");
exit(1);
}

if (i > maxi)
maxi = i;
}

//send and receive
for (i = 1; i <= maxi; i ++) {
if (client[i].fd >= 0 && (client[i].revents & (POLLRDNORM | POLLERR))) {

recv_num = recv(client[i].fd, recv_buf, sizeof(recv_buf), 0);
if (recv_num <= 0) {
close(client[i].fd);
client[i].fd = -1;
} else {
recv_buf[recv_num] = '\0';
memset(send_buf,0,sizeof(send_buf));
sprintf(send_buf, "server proc got %d bytes\n", recv_num);
send_num = send(client[i].fd, send_buf, strlen(send_buf), 0);
if (send_num <= 0) {
close(client[i].fd);
client[i].fd = -1;
}
}
}
}
}

close(sock_fd);
return 0;
}

其实poll函数和select函数差不多的，都是在获取可用描述符处等待，只是select的文件描述符数目受限于操作系统内核设定，我感觉poll函数用起来更加方便些，每个人都各有所好吧。接下来再看看epoll函数