不同端口号加入到同一组播地址，关闭套接字时为什么会有影响？

有两个设备，使用udp组播的方式进行通讯，服务器端建立了两个udp连接，端口号不同，但是加入的是同一组播地址。当我关闭其中一个udp套接字时，为什么会影响另一个udp的连接？

线程a：
int rtp_server_socket;
struct sockaddr_in server_addr,  client_addr;
socklen_t clielen_addr_length;
clielen_addr_length = sizeof(client_addr);

ReSocket:
report_succeed = 1;

 //struct tcp_info info;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(A_PORT);
server_addr.sin_addr.s_addr=htonl(INADDR_ANY);

//create a stream socket
rtp_server_socket = socket(AF_INET, SOCK_DGRAM, 0); //UDP
printf("Create Socket OK \n");

//bind
bind(rtp_server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr))
printf("bind socket ok \n");


    //set Multicast loop
int loop = 1; //1: on , 0: off
setsockopt(rtp_server_socket,IPPROTO_IP,IP_MULTICAST_LOOP,&loop,sizeof(loop));

struct ip_mreq mreq;   
mreq.imr_multiaddr.s_addr = inet_addr(multicast);
mreq.imr_interface.s_addr = htonl(INADDR_ANY);     

//add multicast group
setsockopt(rtp_server_socket, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

int reuse = 1;
setsockopt(rtp_server_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse));

while (1)
{
Recv:
if (0 == report_succeed)
{
            close(rtp_server_socket);
            goto ReSocket;
}
recvfrom(rtp_server_socket, buf, BUFFER_SIZE, 0, (struct sockaddr_in *) &client_addr, &clielen_addr_length);

线程b和上面的一样只是绑定的端口不一样

当我关闭线程b的套接字时，线程a的recvfrom（）函数会堵塞一会，没有数据接收，请问这是为什么？

https://blog.csdn.net/qq_21442277/article/details/55006546