posix multithread.With Multiple threas using one socket to receive data , when will the data be taken away from recv buffer? - multithreading

Question

I use multuple thread to receive data from one socket. they all can receive the same data. I want to know when the data will be taken away from recv buffer? Why does not one thread receive the next data when former thread read former data.
pthread_create(&(ntid[i]), NULL, find_host, (void *)&start_addr);
int find_host(void * arg)
{
int sockfd;
unsigned long ip ;
tv.tv_sec = 0;
tv.tv_usec = 100000;
struct sockaddr_in from;
char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
ip = *(unsigned long *)arg;
struct sockaddr_in present_addr;
if( (sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto) )<0)
{
perror("socket error");
exit(1);
}
setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) );
if(setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv))<0){
printf("socket option SO_RCVTIMEO not support\n");
return;
}
bzero(&present_addr,sizeof(present_addr));
present_addr.sin_family=AF_INET;
present_addr.sin_addr.s_addr = htonl(ip);
pthread_mutex_unlock(&lock);
printf("PING (%s): %d bytes data in ICMP packets.\n",
inet_ntoa(present_addr.sin_addr),ICMP_DATA_LEN);
send_packet(sockfd, sendpacket, present_addr);
recv_packet(sockfd, recvpacket, from);
close(sockfd);
}
void recv_packet(int sockfd, char * recvpacket, struct sockaddr_in from)
{ int n,from_len;
extern int errno;
int nreceived = 0;
struct timeval recv_time;
from_len = sizeof(from);
while (nreceived < MAX_SEND_TIMES)
{
if((n=recvfrom(sockfd,recvpacket, PACKET_SIZE, 0,
(struct sockaddr *)&from,&from_len)) <0)
{
if(errno == EWOULDBLOCK || errno== EAGAIN )
{
printf("recvfrom Timeout!!!!\n");
pthread_exit(NULL);
}
}
gettimeofday(&recv_time,NULL);
if (1 == unpack(recv_time, recvpacket, n, from))
{
printf(" find %u\n", (unsigned short)pthread_self());
nreceived++;
}
else
printf(" not find\n");
}
}