Linux下多进程避免僵尸进程的方法

首先服务端是这样的的，使用父进程进行监听，每当有一个链接到来就开启一个子进程所以程序大概是这个样子的：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

//wait(NULL) 只要有一个子进程退出，那么wait就会返回
//若多个子进程，只能等待一个。

//while (waitpid(-1, NULL, WNOHANG) > 0)
//	;
//WNOHANG 不挂起，如果没有子进程，会返回-1，从而可以跳出循环，信号函数执行完毕

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

ssize_t readn(int fd, void *buf, size_t count)
{
size_t nleft = count;
ssize_t nread;
char *bufp = (char*)buf;

while (nleft > 0)
{
if ((nread = read(fd, bufp, nleft)) < 0)
{
if (errno == EINTR)
continue;
return -1;
}
else if (nread == 0)
return count - nleft;

bufp += nread;
nleft -= nread;
}

return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
size_t nleft = count;
ssize_t nwritten;
char *bufp = (char*)buf;

while (nleft > 0)
{
if ((nwritten = write(fd, bufp, nleft)) < 0)
{
if (errno == EINTR)
continue;
return -1;
}
else if (nwritten == 0)
continue;

bufp += nwritten;
nleft -= nwritten;
}

return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
while (1)
{
int ret = recv(sockfd, buf, len, MSG_PEEK);
if (ret == -1 && errno == EINTR)
continue;
return ret;
}
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
int ret;
int nread;
char *bufp = buf;
int nleft = maxline;
while (1)
{
ret = recv_peek(sockfd, bufp, nleft);
if (ret < 0)
return ret;
else if (ret == 0)
return ret;

nread = ret;
int i;
for (i=0; i<nread; i++)
{
if (bufp[i] == '\n')
{
ret = readn(sockfd, bufp, i+1);
if (ret != i+1)
exit(EXIT_FAILURE);

return ret;
}
}

if (nread > nleft)
exit(EXIT_FAILURE);

nleft -= nread;
ret = readn(sockfd, bufp, nread);
if (ret != nread)
exit(EXIT_FAILURE);

bufp += nread;
}

return -1;
}

void echo_srv(int conn)
{
char recvbuf[1024];
        while (1)
        {
                memset(recvbuf, 0, sizeof(recvbuf));
                int ret = readline(conn, recvbuf, 1024); 
if (ret == -1)
ERR_EXIT("readline");
if (ret == 0)
{
printf("client close\n");
//发现对方关闭时自己也关闭
close(conn);
break;
}

                fputs(recvbuf, stdout);
                writen(conn, recvbuf, strlen(recvbuf));
                
             
        }
}

//原因如上
void handle_sigchld(int sig)
{
int mypid = 0;

while ( (mypid=waitpid(-1, NULL, WNOHANG)) >0 )
{
printf("父进程等待子进程退出:%d \n", mypid);
}
}
int main(void)
{
    	signal(SIGCHLD, SIG_IGN);

signal(SIGCHLD, handle_sigchld);
int listenfd;
if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
ERR_EXIT("socket");

struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(8001);
//servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
/*inet_aton("127.0.0.1", &servaddr.sin_addr);*/

int on = 1;
if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
ERR_EXIT("setsockopt");

if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
ERR_EXIT("bind");

if (listen(listenfd, SOMAXCONN) < 0)
ERR_EXIT("listen");

struct sockaddr_in peeraddr;
socklen_t peerlen = sizeof(peeraddr);
int conn;

pid_t pid;
while (1)
{	//父进程监听
if ((conn = accept(listenfd, (struct sockaddr*)&peeraddr, &peerlen)) < 0)
ERR_EXIT("accept");

printf("ip=%s port=%d\n", inet_ntoa(peeraddr.sin_addr), ntohs(peeraddr.sin_port));

pid = fork();
if (pid == -1)
ERR_EXIT("fork");
if (pid == 0)  //子进程与客户端建立链接
{
close(listenfd);
echo_srv(conn);
exit(EXIT_SUCCESS);
}
else{
close(conn); //父进程也有一份连接，需要关闭
}

}
return 0;
}

顺便给出client的代码，共同复用的函数在上面已经给出下面只贴上主要代码：

void echo_cli(int sock)
{
char sendbuf[1024] = {0};
char recvbuf[1024] = {0};
while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
{
writen(sock, sendbuf, strlen(sendbuf));

int ret = readline(sock, recvbuf, sizeof(recvbuf));
if (ret == -1)
ERR_EXIT("readline");
else if (ret == 0)
{
printf("client close\n");
break;
}

fputs(recvbuf, stdout);
memset(sendbuf, 0, sizeof(sendbuf));
memset(recvbuf, 0, sizeof(recvbuf));
}

close(sock);
}

int main(void)
{
int sock;
if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
ERR_EXIT("socket");

struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(8001);
servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");

if (connect(sock, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
ERR_EXIT("connect");

struct sockaddr_in localaddr;
socklen_t addrlen = sizeof(localaddr);
if (getsockname(sock, (struct sockaddr*)&localaddr, &addrlen) < 0)
ERR_EXIT("getsockname");

printf("ip=%s port=%d\n", inet_ntoa(localaddr.sin_addr), ntohs(localaddr.sin_port));

echo_cli(sock);

return 0;
}

以上在client关闭时，server 也可以正常关闭

结语：

建立链接很简单，但是关闭链接需要小心，close()函数是引用计数型的，而且socket链接也是可以复制的，所以需要小心拷贝复制！！！

不足之处 请务必指出，感谢