在研究TCP IP的11种状态之前，我们先看一下服务器中存在僵尸进程的情况。
服务器是多进程模型，客户端是单进程。
服务器程序如下：
1 #include <sys/types.h>
2 #include <unistd.h>
3 #include <stdlib.h>
4 #include <stdio.h>
5 #include <string.h>
6 #include <errno.h>
7 #include <arpa/inet.h>
8 #include <sys/socket.h>
9 #include <netinet/in.h>
10 #include <sys/socket.h>
11 #include <netinet/ip.h> /* superset of previous */
12
13
14 int main()
15 {
16 int sockfd = 0;
17 sockfd = socket(AF_INET, SOCK_STREAM, 0);
18
19 if(sockfd == -1)
20 {
21 perror("socket error");
22 exit(0);
23 }
24
25 struct sockaddr_in addr;
26 addr.sin_family = AF_INET;
27 addr.sin_port = htons(8001);
28 inet_aton("192.168.31.128", &addr.sin_addr);
29 //addr.sin_addr.s_addr = inet_addr("192.168.6.249");
30 //addr.sin_addr.s_addr = INADDR_ANY;
31
32 int optval = 1;
33 if( setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0)
34 {
35 perror("setsockopt error");
36 exit(0);
37 }
38
39 if( bind(sockfd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
40 {
41 perror("bind error");
42 exit(0);
43 }
44
45 if(listen(sockfd, SOMAXCONN) < 0)
46 {
47 perror("listen error");
48 exit(0);
49 }
50
51 struct sockaddr_in peeraddr;
52 socklen_t peerlen;
53
54 int conn = 0;
55
56 while(1)
57 {
58 conn = accept(sockfd, (struct sockaddr *)&peeraddr, &peerlen);
59 if(conn == -1)
60 {
61 perror("accept error");
62 exit(0);
63 }
64
65 char *p = NULL;
66 int peerport = 0;
67 p = inet_ntoa(peeraddr.sin_addr);
68 peerport = ntohs(peeraddr.sin_port);
69 printf("peeraddr = %s\n peerport = %d\n", p, peerport);
70
71 pid_t pid = fork();
72
73 if(pid == -1)
74 {
75 perror("fork error");
76 exit(0);
77 }
78
79 if(pid == 0)
80 {
81 char recvbuf[1024] = {0};
82 int ret = 0;
83 while(1)
84 {
85 ret = read(conn, recvbuf, sizeof(recvbuf));
86
87 if(ret == 0)
88 {
89 printf("peer closed \n");
90 exit(0);
91 }
92 else if(ret < 0)
93 {
94 perror("read error");
95 exit(0);
96 }
97
98 fputs(recvbuf, stdout);
99
100 write(conn, recvbuf, ret);
101 }
102 }
103 }
104
105 close(conn);
106 close(sockfd);
107
108 return 0;
109 }
客户端程序如下：
1 #include <sys/types.h>
2 #include <unistd.h>
3 #include <stdlib.h>
4 #include <stdio.h>
5 #include <string.h>
6 #include <errno.h>
7 #include <arpa/inet.h>
8 #include <sys/socket.h>
9 #include <netinet/in.h>
10 #include <sys/socket.h>
11 #include <netinet/ip.h> /* superset of previous */
12
13 int main()
14 {
15 int sockfd = 0;
16 sockfd = socket(AF_INET, SOCK_STREAM, 0);
17
18 struct sockaddr_in addr;
19 addr.sin_family = AF_INET;
20 addr.sin_port = htons(8001);
21 inet_aton("192.168.31.128", &addr.sin_addr);
22 //addr.sin_addr.s_addr = inet_addr("192.168.31.128");
23
24 if( connect(sockfd, (struct sockaddr *)&addr, sizeof(addr)) == -1 )
25 {
26 perror("connect error");
27 exit(0);
28 }
29
30 char recvbuf[1024] = {0};
31 char sendbuf[1024] = {0};
32 int ret = 0;
33
34 while(fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
35 {
36 write(sockfd, sendbuf, strlen(sendbuf));
37
38 ret = read(sockfd, recvbuf, sizeof(recvbuf));
39
40 fputs(recvbuf, stdout);
41 memset(recvbuf, 0, sizeof(recvbuf));
42 memset(sendbuf, 0, sizeof(sendbuf));
43
44 }
45
46 close(sockfd);
47
48 return 0;
49 }
执行结果如下：
可以看到，当客户端使用ctrl+c关闭时，服务器中的子进程成了僵尸进程。这是因为，子进程死了，但是没有进程给它收尸，我们可以调用signal(SIGCHLD, SIG_IGN)函数告诉内核，忽略SIGCHLD信号，让内核来处理SIGCHLD信号，也即让内核收尸，但是工程中一般不这样做。一般是注册信号让父进程调用wait来收尸。
修改服务器程序，加入信号处理函数，如下所示：
1 #include <sys/types.h>
2 #include <unistd.h>
3 #include <stdlib.h>
4 #include <stdio.h>
5 #include <string.h>
6 #include <errno.h>
7 #include <signal.h>
8 #include <arpa/inet.h>
9 #include <sys/socket.h>
10 #include <netinet/in.h>
11 #include <sys/socket.h>
12 #include <netinet/ip.h> /* superset of previous */
13
14 void handler(int num)
15 {
16 printf("child die\n");
17 wait(NULL);
18 }
19
20 int main()
21 {
22 int sockfd = 0;
23 signal(SIGCHLD, handler);
24 sockfd = socket(AF_INET, SOCK_STREAM, 0);
25
26 if(sockfd == -1)
27 {
28 perror("socket error");
29 exit(0);
30 }
31
32 struct sockaddr_in addr;
33 addr.sin_family = AF_INET;
34 addr.sin_port = htons(8001);
35 inet_aton("192.168.31.128", &addr.sin_addr);
36 //addr.sin_addr.s_addr = inet_addr("192.168.6.249");
37 //addr.sin_addr.s_addr = INADDR_ANY;
38
39 int optval = 1;
40 if( setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0)
41 {
42 perror("setsockopt error");
43 exit(0);
44 }
45
46 if( bind(sockfd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
47 {
48 perror("bind error");
49 exit(0);
50 }
51
52 if(listen(sockfd, SOMAXCONN) < 0)
53 {
54 perror("listen error");
55 exit(0);
56 }
57
58 struct sockaddr_in peeraddr;
59 socklen_t peerlen;
60
61 int conn = 0;
62
63 while(1)
64 {
65 conn = accept(sockfd, (struct sockaddr *)&peeraddr, &peerlen);
66 if(conn == -1)
67 {
68 perror("accept error");
69 exit(0);
70 }
71
72 char *p = NULL;
73 int peerport = 0;
74 p = inet_ntoa(peeraddr.sin_addr);
75 peerport = ntohs(peeraddr.sin_port);
76 printf("peeraddr = %s\n peerport = %d\n", p, peerport);
77
78 pid_t pid = fork();
79
80 if(pid == -1)
81 {
82 perror("fork error");
83 exit(0);
84 }
85
86 if(pid == 0)
87 {
88 char recvbuf[1024] = {0};
89 int ret = 0;
90 while(1)
91 {
92 ret = read(conn, recvbuf, sizeof(recvbuf));
93
94 if(ret == 0)
95 {
96 printf("peer closed \n");
97 exit(0);
98 }
99 else if(ret < 0)
100 {
101 perror("read error");
102 exit(0);
103 }
104
105 fputs(recvbuf, stdout);
106
107 write(conn, recvbuf, ret);
108 }
109 }
110 }
111
112 close(conn);
113 close(sockfd);
114
115 return 0;
116 }
执行结果如下：
由上图可以看到服务器中子进程死掉后，不存在僵尸进程。而且服务器还正常工作，我们重启客户端，依然可以正常发送数据。
原文地址：https://www.cnblogs.com/wanmeishenghuo/p/9403359.html
时间： 2024-07-31 05:32:03