linux socket accept can't been blocked - linux

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
int main()
{
int server_sockfd,client_sockfd;
int server_len,client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address;
create a new socket
unlink("server_socket");
server_sockfd=socket(AF_INET,SOCK_STREAM,0);
name it
server_address.sin_family=AF_INET;
server_address.sin_addr.s_addr=htonl(INADDR_ANY);
server_address.sin_port=htons(9734);
server_len=sizeof(server_address);
bind(server_sockfd,(struct sockaddr *)&server_address,server_len);
set block
int flags=fcntl(server_sockfd,F_GETFL,0);
if(flags&O_NONBLOCK==1){
printf("NONBLOCK");
}else{
printf("BLOCK");
}
flags=flags&~O_NONBLOCK;
fcntl(server_sockfd,F_SETFL,flags);
if(flags&O_NONBLOCK==1){
printf("NONBLOCK");
}else{
printf("BLOCK");
}
listen
listen(server_sockfd,5);
while(1){
char ch;
printf("server waiting\n");
client_len=sizeof(client_address);
client_sockfd=
accept(server_sockfd,(struct sockaddr*)&client_sockfd,&client_len);
it is blocked at first time
read(client_sockfd,&ch,1);
ch++;
write(client_sockfd,&ch,1);
close(client_sockfd);
}
}
when the client connected first,I work,but the next won't work

Answer 1

A mismatch may occurs between client_address and client_sockfd.
The man page of accept() says:
int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
The addrlen argument is a value-result argument: the caller must initialize it to
contain the size (in bytes) of the structure pointed to by addr; on return it
will contain the actual size of the peer address.
Try:
client_sockfd=
accept( server_sockfd, (struct sockaddr*)&client_address, &client_len );