我在下面编写了 UDP 客户端，它基本上生成一个单独的线程来接收数据报，但是数据报仅在主线程中发送。现在，在 Linux 发行版上实例化（“./udpClient 1”）UDP 客户端后按 ctrl^D，实现退出循环（围绕 getline () 调用）并关闭套接字描述符。
我观察到，尽管在描述符上调用 close，但直到客户端进程终止并且仍然看到执行“netstat -an|grep udp”的相关条目时，才会释放相同的描述符。但是，如果我注释/删除代码以生成接收器线程，则套接字描述符将在调用 close() 后立即释放。
似乎套接字引用计数在生成一个单独的线程（它基本上接收并阻塞所述套接字描述符）时增加，因此 close () 调用什么也不做。
这是需要的吗，因为我知道如果套接字描述符在进程之间共享而不是在线程之间共享，套接字引用计数就会增加？是否是因为 Linux 将线程实现为 LWP？如果是，这是否是期望的行为？
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
void *receiver (void *arg);
int sockfd;
int doConnect = 0;
int
main (int argc, char *argv[])
{
pthread_t thrid;
struct sockaddr_in servaddr;
struct sockaddr_in clntaddr;
char *line;
size_t len = 0;
size_t read;
if (argc < 4)
{
printf
("Usage:%s <Server Ipv4 address> <Server Port> <Connect Yes(1)/No(0)> [Client IPv4 address] [Client Port]\n",
argv[0]);
return -1;
}
/*
* AF_INET, AF_INET6, AF_UNIX, AF_NETLINK
* SOCK_STREAM (TCP), SOCK_DGRAM (UDP), SOCK_RAW
*/
if ((sockfd = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
{
printf ("Failed to create socket: %s\n", strerror (errno));
return -1;
}
bzero (&clntaddr, sizeof (struct sockaddr_in));
if (argc == 6)
{
printf ("doing bind......\n");
clntaddr.sin_family = AF_INET;
clntaddr.sin_port = htons (atoi (argv[5]));
inet_aton (argv[4], &clntaddr.sin_addr);
if (bind
(sockfd, (struct sockaddr *) &clntaddr,
sizeof (struct sockaddr_in)) == -1)
{
printf ("Failed to bind: %s\n", strerror (errno));
close (sockfd);
return -1;
}
}
/*
* fill up the server details
*/
bzero (&servaddr, sizeof (struct sockaddr_in));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons (atoi (argv[2]));
inet_aton (argv[1], &servaddr.sin_addr);
doConnect = atoi (argv[3]);
if (1 == doConnect)
{
printf ("doing connect......\n");
if (-1 ==
connect (sockfd, (struct sockaddr *) &servaddr,
sizeof (struct sockaddr_in)))
{
printf ("Failed to connect: %s\n", strerror (errno));
close (sockfd);
return -1;
}
}
if (pthread_create (&thrid, NULL, receiver, NULL) < 0)
{
printf ("Failed to create thread: %s\n", strerror (errno));
close (sockfd);
return -1;
}
while ((read = getline (&line, &len, stdin)) != -1)
{
if (1 == doConnect)
{
if (send (sockfd, line, len, 0) < 0)
{
printf ("send () failed: %s\n", strerror (errno));
}
}
else
{
if (sendto (sockfd, line, len, 0, (struct sockaddr *) &servaddr,
sizeof (struct sockaddr_in)) < 0)
{
printf ("sendto () failed: %s\n", strerror (errno));
}
}
}
if (line)
free (line);
close (sockfd);
printf ("socket is closed.....\n");
sleep (60);
}
void *
receiver (void *arg)
{
char buff[512];
while (1)
{
memset (buff, 0, sizeof (buff));
if (1 == doConnect)
{
if (recv (sockfd, buff, sizeof (buff), 0) < 0)
{
// printf ("recvfrom () failed: %s\n", strerror (errno));
printf ("recv () failed\n");
}
else
{
printf ("recv () returned: %s\n", buff);
}
}
else
{
if (recvfrom (sockfd, buff, sizeof (buff), 0, NULL, NULL) < 0)
{
// printf ("recvfrom () failed: %s\n", strerror (errno));
printf ("recvfrom () failed\n");
}
else
{
printf ("recvfrom () returned: %s\n", buff);
}
}
}
}
