How to remove an extra cycle? - c

Question

I need to make the code more readable, but it has a lot of cycle, can I fix this somehow?
The variable i constantly jumps there and there, it is very inconvenient to watch in debugging.
for(;;)
{
//
// For connection orientated protocols, we will handle the
// packets received from a connection collectively. For datagram
// protocols, we have to handle each datagram individually.
//
//
// Check to see if we have any sockets remaining to be served
// from previous time through this loop. If not, call select()
// to wait for a connection request or a datagram to arrive.
//
for (i = 0; i < numSocket; i++)
{
if (FD_ISSET(servSock[i], &SockSet))
break;
}
if (i == numSocket)
{
for (i = 0; i < numSocket; i++)
{
FD_SET(servSock[i], &SockSet);
}
if (select(numSocket, &SockSet, 0, 0, 0) == SOCKET_ERROR)
continue;
}
for (i = 0; i < numSocket; i++)
{
if (FD_ISSET(servSock[i], &SockSet))
{
FD_CLR(servSock[i], &SockSet);
break;
}
}
...
}

Answer 1

To make the code more readable (and testable and maintainable) you can encapsulate some of the logic into separate functions with meaningful names. Consider this version of your loop
for(;;)
{
int i = find_socket_to_be_served(numSocket, servSock, &SockSet);
if (i == numSocket)
{
set_all_sockets(numSocket, servSock, &SockSet);
if (select(numSocket, &SockSet, 0, 0, 0) == SOCKET_ERROR)
continue;
}
// ...
}
Where the two functions used are defined as
int find_socket_to_be_served(int n_sockets, int *fds, fd_set *fdset)
{
int i = 0;
for (; i < n_sockets; i++)
{
if (FD_ISSET(fds[i], fdset))
{
FD_CLR(fds[i], fdset);
break;
}
}
return i;
}
void set_all_sockets(int n_sockets, int *fds, fd_set *fdset)
{
for (int i = 0; i < n_sockets; i++)
{
FD_SET(fds[i], fdset);
}
}

Answer 2

As far as I understand your code, you don't need FD_CLEAR() your sockets one by one.
Just FD_ZERO() all of them at once, then use a single loop to FD_SET() them again.
Note that after select(), many sockets could be ready to use; you don't have to break when one has been used.
Note also that the first parameter of select() is unused on Windows but should be 1+ the max of your socket file descriptors (not the number of them) everywhere else.
for(;;)
{
FD_ZERO(&SockSet);
for (int i = 0; i < numSocket; i++)
{
FD_SET(servSock[i], &SockSet);
}
if (select(numSocket, &SockSet, 0, 0, 0) == SOCKET_ERROR)
continue; // or probably break...
}
for (int i = 0; i < numSocket; i++)
{
if (FD_ISSET(servSock[i], &SockSet))
{
// use servSock[i]
}
}
}