Segmentation fault in accept system call - c

Question

I have the following code serving as main loop for a server that accepts incoming socket connections.
At the moment the macro OperationMode is defined as 1 so it will execute the pthread logic.
for (hit = 1 ;; hit++) {
printf("Got here\n\n");
length = sizeof(cli_addr);
/* block waiting for clients */
socketfd = accept(listenfd, (struct sockaddr *) &cli_addr, &length);
if (socketfd < 0)
printf("ERROR system call - accept error\n");
else
{
printf("Testing\n\n\n");
#ifdef OperationMode
pthread_t thread_id;
if(pthread_create(&thread_id, NULL, attendFTP(socketfd, hit), NULL))
{
perror("could not create thread");
return 1;
}
#else
pid = fork();
if(pid==0)
{
ftp(socketfd, hit);
}
else
{
close(socketfd);
kill(pid, SIGCHLD);
}
#endif
}
}
I'm able to create a thread for the first incoming socket connection but once I iterate over the loop I get segmentation fault error in the line
socketfd = accept(listened, (struct sockaddr *) &cli_addr, &length);
My attendFTP function has the following code
void *attendFTP(int fd, int hit)
{
ftp(fd, hit);
return NULL;
}
This works perfect for the fork implementation. How can I fix the segmentation fault error?

Answer 1

pthread_create(&thread_id, NULL, attendFTP(socketfd, hit), NULL);
This code passess result of a call to attendFTP() with given paramters - and this result is always NULL.
So pthread_create is trying to launch a function at NULL address and, correspondingly, fails.
If you run your compiler with -pedantic argument, compiler will tell you that what you are doing is wrong. Without -pedantic, gcc allows for some 'extensions', which might hide errors. Btw, this is why -pedantic is, in my view, a must.
What you actually want is to pass some arguments to your threading function. Unfortunately, it is really convoluted in C pthreads, and requires you to allocate and deallocate the said struct. Something like this:
struct args {
int fd;
int hit;
};
...
pthread_t thread_id;
struct args* args = malloc(sizeof(struct args));
args->fd = socketfd;
args->hit = hit;
if(pthread_create(&thread_id, NULL, attendFTP, args))
....
void* attendFTP(void* vargs)
{
struct args* args = vargs;
ftp(args->fd, args->hit);
free(args);
return NULL;
}