How to receive and send in different threads with C sockets - c

Question

I am trying to send and receive in different threads. When I use the code below I get a bad address error, I guess because my server address could not be properly passed to the thread function.
Code:
#include "client.h"
struct global_table{
struct sockaddr_in *serveraddr;
int sockID;
};
void *recvFromServer(struct global_table *rec){
char recBuf[RECVBUFSIZE];
int serverSize = sizeof(rec->serveraddr);
while(1)
{
int n = recvfrom(rec->sockID, recBuf, RECVBUFSIZE, 0, &rec->serveraddr, &serverSize);
if (n < 0)
perror("ERROR in recvfrom");
decryptData(recBuf);
printf("Recieved: %s\n", recBuf);
pthread_exit(NULL);
}
}
void pingServer(char *hostname, int portno)
{
int sockfd, n, serverlen;
struct sockaddr_in serveraddr;
struct sockaddr_in client_addr;
struct hostent *server;
char *buf;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0)
perror("ERROR opening socket");
server = gethostbyname(hostname);
if (server == NULL)
perror("ERROR, no host found");
bzero((char *) &serveraddr, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
bcopy((char *)server->h_addr, (char *)&serveraddr.sin_addr.s_addr, server->h_length);
serveraddr.sin_port = htons(portno);
client_addr.sin_family = AF_INET;
client_addr.sin_addr.s_addr = htonl(INADDR_ANY);
client_addr.sin_port = htons(5500);
if (bind(sockfd,(struct sockaddr *)&client_addr, sizeof(struct sockaddr)) == -1)
perror("Socket could not be binded");
if(setsockopt(sockfd,IPPROTO_IP,IP_TOS,&tos,sizeof(tos)))
perror("Could not set socket option");
pthread_t threads[2];
serverlen = sizeof(serveraddr);
struct global_table server_info;
server_info.sockID = sockfd;
server_info.serveraddr = &serveraddr;
pthread_create(&threads[0],NULL,recvFromServer, &server_info); // Trying to recv on a different thread
pthread_join(threads[0],NULL);
}
int main(int argc, char **argv) {
char *hostname;
int portno;
if (argc != 3)
perror("usage: <hostname> <port>\n");
hostname = argv[1];
portno = atoi(argv[2]);
pingServer(hostname, portno);
return 0;
}
How can I fix the problem?

Answer 1

In addition to the problems noted in the comments (and by now, this problem is also noted in the comments...), this line
struct global_table server_info;
creates a local variable in your pingServer() function.
This line
pthread_create(&threads[0],NULL,recvFromServer, &server_info); // Trying to recv on a different thread
of code passes the address of that variable to the recvFromServer() function, which will run in a different thread. But then pingServer() immediately returns and the local server_info variable ceases to exist.
One fix is to define the server_info and serveraddr variable as static:
static struct global_table server_info;
static struct sockaddr_in serveraddr;
That will create one copy of the server_info variable that will be shared by every invocation of pingServer(), but that one copy will exist for the lifetime of your program.