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 <arpa/inet.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);
while(1) {
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) {
Close(connfd);
} else {
perr_exit("fork");
}
}
}
}
client.c
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "wrap.h"
#define MAXLINE 80
#define SERV_PORT 8000
int main(int argc,char *argv[]) {
struct sockaddr_in servaddr;
char buf[MAXLINE];
int sockfd,n;
sockfd = Socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
inet_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr.s_addr);
servaddr.sin_port = htons(SERV_PORT);
Connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
while(fgets(buf,MAXLINE,stdin) != NULL) {
Write(sockfd,buf,strlen(buf));
n = Read(sockfd,buf,MAXLINE);
if(n == 0) {
printf("the other side has ben closed.\n");
} else {
Write(STDOUT_FILENO,buf,n);
}
}
Close(sockfd);
return 0;
}
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)
{
int n;
if ( (n = socket(family, type, protocol)) < 0)
perr_exit("socket error");
return n;
}
ssize_t Read(int fd, void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = read(fd, ptr, nbytes)) == -1) {
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = write(fd, ptr, nbytes)) == -1) {
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
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) {
if (errno == EINTR)
nread = 0;
else
return -1;
} else if (nread == 0)
break;
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;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
if (nwritten < 0 && errno == EINTR)
nwritten = 0;
else
return -1;
}
nleft -= nwritten;
ptr += nwritten;
}
return n;
}
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) {
again:
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
if (errno == EINTR)
goto again;
return -1;
} else if (read_cnt == 0)
return 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;
ptr = vptr;
for (n = 1; n < maxlen; n++) {
if ( (rc = my_read(fd, &c)) == 1) {
*ptr++ = c;
if (c == '\n')
break;
} else if (rc == 0) {
*ptr = 0;
return n - 1;
} else {
return -1;
}
}
*ptr = 0;
return n;
}
运行结果（编译server）：
运行client端