1多进程并发服务器
使用多进程并发服务器时要考虑以下几点：
a.父最大文件描述个数（父进程中需要close关闭accept返回的新文件描述符）
b.系统内创建进程个数（和内存大小相关）
c.进程创建过多是否降低整体服务性能（进程调度）
2.案例说明
server.c,代码如下：
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <ctype.h>
#include <unistd.h>
#include "wrap.h"
#define maxline 80
#define serv_port 8000
void do_sigchild(int num) {
waitpid(0,null,wnohang);
}
int main(void) {
struct sockaddr_in servaddr,cliaddr;
socklen_t cliaddr_len;
int listenfd,connfd;
char buf[maxline];
//inet_addrstrlen是ip地址的最大长度，是系统定义的一个宏
char str[inet_addrstrlen];
int i,n;
pid_t pid;
struct sigaction newact;
newact.sa_handler = do_sigchild;
sigemptyset(&newact.sa_mask);
newact.sa_flags = 0;
//发信号
sigaction(sigchld,&newact,null);
//1.这里建立一个tcp的连接，因为是sock_stream的，表示的是tcp的
listenfd = socket(af_inet,sock_stream,0);
//将seraddr内容清零
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = af_inet;
servaddr.sin_addr.s_addr = htonl(inaddr_any);
servaddr.sin_port = htons(serv_port);
//2.绑定ip地址和端口号
bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
//监听，最多的可以是20个
listen(listenfd,20);
printf("accepting connections...\n");
while(1) {
cliaddr_len = sizeof(cliaddr_len);
//connfd:这里才是后续进程需要用的文件描述符
//listenfd:已经不用里，可以被销毁,这个程序是在子进程里面销毁
connfd = accept(listenfd,(struct sockaddr *)&cliaddr,&cliaddr_len);
pid = fork();
if(pid ==0) {
if(pid == 0) {
close(listenfd);
n = read(connfd,buf,maxline);
if(n == 0) {
printf("the other side has been closed.\n");
break;
printf("received from %s at port %d\n",
inet_ntop(af_inet,&cliaddr.sin_addr.s_addr,str,sizeof(str)),
ntohs(cliaddr.sin_port));
for(i = 0; i< n; i++) {
buf[i] = toupper(buf[i]);
write(connfd,buf,n);
close(connfd);
return 0;
} else if(pid > 0) {
} else {
perr_exit("fork");
client.c
int main(int argc,char *argv[]) {
struct sockaddr_in servaddr;
int sockfd,n;
sockfd = socket(af_inet,sock_stream,0);
inet_pton(af_inet,"127.0.0.1",&servaddr.sin_addr.s_addr);
connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
while(fgets(buf,maxline,stdin) != null) {
write(sockfd,buf,strlen(buf));
n = read(sockfd,buf,maxline);
printf("the other side has ben closed.\n");
write(stdout_fileno,buf,n);
close(sockfd);
wrap.h
#ifndef __wrap_h_
#define __wrap_h_
void perr_exit(const char *s);
int accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
void bind(int fd, const struct sockaddr *sa, socklen_t salen);
void connect(int fd, const struct sockaddr *sa, socklen_t salen);
void listen(int fd, int backlog);
int socket(int family, int type, int protocol);
ssize_t read(int fd, void *ptr, size_t nbytes);
ssize_t write(int fd, const void *ptr, size_t nbytes);
void close(int fd);
ssize_t readn(int fd, void *vptr, size_t n);
ssize_t writen(int fd, const void *vptr, size_t n);
static ssize_t my_read(int fd, char *ptr);
ssize_t readline(int fd, void *vptr, size_t maxlen);
#endif
wrap.c
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
void perr_exit(const char *s)
{
perror(s);
exit(1);
int accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
int n;
again:
if ( (n = accept(fd, sa, salenptr)) < 0) {
if ((errno == econnaborted) || (errno == eintr))
goto again;
else
perr_exit("accept error");
return n;
void bind(int fd, const struct sockaddr *sa, socklen_t salen)
if (bind(fd, sa, salen) < 0)
perr_exit("bind error");
void connect(int fd, const struct sockaddr *sa, socklen_t salen)
if (connect(fd, sa, salen) < 0)
perr_exit("connect error");
void listen(int fd, int backlog)
if (listen(fd, backlog) < 0)
perr_exit("listen error");
int socket(int family, int type, int protocol)
if ( (n = socket(family, type, protocol)) < 0)
perr_exit("socket error");
ssize_t read(int fd, void *ptr, size_t nbytes)
ssize_t n;
if ( (n = read(fd, ptr, nbytes)) == -1) {
if (errno == eintr)
return -1;
ssize_t write(int fd, const void *ptr, size_t nbytes)
if ( (n = write(fd, ptr, nbytes)) == -1) {
void close(int fd)
if (close(fd) == -1)
perr_exit("close error");
ssize_t readn(int fd, void *vptr, size_t n)
size_t nleft;
ssize_t nread;
char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nread = read(fd, ptr, nleft)) < 0) {
nread = 0;
} else if (nread == 0)
nleft -= nread;
ptr += nread;
return n - nleft;
ssize_t writen(int fd, const void *vptr, size_t n)
size_t nleft;
ssize_t nwritten;
const char *ptr;
if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
if (nwritten < 0 && errno == eintr)
nwritten = 0;
nleft -= nwritten;
ptr += nwritten;
static ssize_t my_read(int fd, char *ptr)
static int read_cnt;
static char *read_ptr;
static char read_buf[100];
if (read_cnt <= 0) {
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
} else if (read_cnt == 0)
read_ptr = read_buf;
read_cnt--;
*ptr = *read_ptr++;
return 1;
ssize_t readline(int fd, void *vptr, size_t maxlen)
ssize_t n, rc;
char c, *ptr;
for (n = 1; n < maxlen; n++) {
if ( (rc = my_read(fd, &c)) == 1) {
*ptr++ = c;
if (c == '\n')
} else if (rc == 0) {
*ptr = 0;
return n - 1;
*ptr = 0;
运行结果（编译server）：
运行client端