How to get poll()'s POLLHUP equivalent with select()? - c++

Question

I'm currently porting some code from Linux to Windows (with MinGW).
From what I understand, MinGW doesn't support poll(), which was used in the original, so I'm rewriting everything for select().
And now I stumbled upon if (pfd[i].revents & (POLLERR|POLLHUP))...
How can I get the equivalent of this condition with select() - or alternatively, with whatever the winsock api or MinGW provides? The POLLERR part is simple enough; if(FD_ISSET (i, &error_fd_set)) but I'm at loss about the POLLHUP part.

Answer 1

You can't. You have to use the "normal" way to find out whether the connection has been closed, that is reading from it.
In terms of code it'd be:
int rc = select(max_fd + 1, read_set, ..., ..., ...);
// check rc
for (int i = 0; i <= max_fd; ++i) {
if (FD_ISSET(i, &read_set)) { // data incoming on i
int rc = read(i, ..., ...); // or recv, if you use some flag
if (rc == 0) {
// i hung up
}
}
}
Otherwise, you can use WSAPoll which offers an API like the one you'd expect in UNIX-like systems.
Further information on WSAPoll.

Answer 2

According to my copy of The Linux Programming Interface, kernel poll events are mapped to select() events like so:
// Ready for reading
#define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
// Ready for writing
#define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
// Exceptional condition
#define POLLEX_SET (POLLPRI)
So this suggests that you need to check the 'ready' event. To actually distinguish between POLLHUP, POLLIN, and POLLIN | POLLHUP, you can use the following chart from the book:
| ----- Condition or event ---- |
Data in pipe? | Write end open? | select() | poll()
no no r | POLLHUP
yes yes r | POLLIN
yes no r | POLLIN | POLLHUP