linux系统父子进程共享端口
nginx 就是使用了父子进程 共享端口，所以nginx快速这个也算一个原因

#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main()
{
int sfp,nfp;
struct sockaddr_in s_add,c_add;
int sin_size;
unsigned short portnum=8888;

printf("Hello,welcome to my server !\r\n");
sfp = socket(AF_INET, SOCK_STREAM, 0);
if(-1 == sfp)
{
    printf("socket fail ! \r\n");
    return -1;
}
printf("socket ok !\r\n");


bzero(&s_add,sizeof(struct sockaddr_in));
s_add.sin_family=AF_INET;
s_add.sin_addr.s_addr=htonl(INADDR_ANY);
s_add.sin_port=htons(portnum);

if(-1 == bind(sfp,(struct sockaddr *)(&s_add), sizeof(struct sockaddr)))
{
    printf("bind fail !\r\n");
    return -1;
}
printf("bind ok !\r\n");

if(-1 == listen(sfp,5))
{
    printf("listen fail !\r\n");
    return -1;
}
printf("listen ok\r\n");

fork();
while(1)
{
sin_size = sizeof(struct sockaddr_in);

nfp = accept(sfp, (struct sockaddr *)(&c_add), &sin_size);
printf("\t\t\t\t\t\tprocess is %ld\n",(long)getpid());
if(-1 == nfp)
{
    printf("accept fail !\r\n");
    return -1;
}
printf("accept ok!\r\nServer start get connect from %#x : %#x\r\n",ntohl(c_add.sin_addr.s_addr),ntohs(c_add.sin_port));


if(-1 == write(nfp,"hello,welcome to my server \r\n",32))
{
    printf("write fail!\r\n");
    return -1;
}
printf("write ok!\r\n");
close(nfp);

}
close(sfp);
return 0;
}

客户端
#include <stdlib.h>
#include <sys/types.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main()
{
int cfd;
int recbytes;
int sin_size;
char buffer[1024]={0};  
struct sockaddr_in s_add,c_add;
unsigned short portnum=8888;

printf("Hello,welcome to client !\r\n");

cfd = socket(AF_INET, SOCK_STREAM, 0);
if(-1 == cfd)
{
    printf("socket fail ! \r\n");
    return -1;
}
printf("socket ok !\r\n");

bzero(&s_add,sizeof(struct sockaddr_in));
s_add.sin_family=AF_INET;
s_add.sin_addr.s_addr= inet_addr("127.0.0.1");
s_add.sin_port=htons(portnum);
printf("s_addr = %#x ,port : %#x\r\n",s_add.sin_addr.s_addr,s_add.sin_port);


if(-1 == connect(cfd,(struct sockaddr *)(&s_add), sizeof(struct sockaddr)))
{
    printf("connect fail !\r\n");
    return -1;
}
printf("connect ok !\r\n");

if(-1 == (recbytes = read(cfd,buffer,1024)))
{
    printf("read data fail !\r\n");
    return -1;
}
printf("read ok\r\nREC:\r\n");

buffer[recbytes]='\0';
printf("%s\r\n",buffer);

getchar();
close(cfd);
return 0;
}

分别多次运行客户端，可以发现显示的进程号是不同的

Hello,welcome to my server !
socket ok !
bind ok !
listen ok
process is 3277
accept ok!
Server start get connect from 0x7f000001 : 0xc67d
write ok!
process is 3278
accept ok!
Server start get connect from 0x7f000001 : 0xc681
write ok!
process is 3277
accept ok!
Server start get connect from 0x7f000001 : 0xc682
write ok!
process is 3278
accept ok!
Server start get connect f