On Sat, Sep 29, 2007 at 03:11:18PM -0700, Davide Libenzi wrote:
>
> Heh? Wait for read&write? Consider such code:
>
> for (;;) {
> err = SSL_shutdown();
> code = SSL_get_error(ssl, err);
> if (code == SSL_ERROR_SYSCALL) {
> select(SSL_get_fd(ssl), RDWR);
This is not how select() works, but I assume you know that and are
intentionally writing pseudocode. However, what it elides is that,
generally, applications using select() for nonblocking I/O are managing
many sockets at once. In practice, selecting on one of those sockets in
both directions when you only care about one direction is almost zero
cost.
> continue;
> }
> ...
> }
>
> Now consider a typical case, where, just for example, our notify-close is
> already gone and we're wating for the peer notify-close. Output buffer are
> empty, so the select(RDWR) returns immediately every time you call it.
Obviously, if you're shutting down, and the socket's returned ready for
write once, you select only for read; the corresponsing condition is true
in the opposite direction.
Yes, it's a stupid API. Yes, it's a nuisance to work around it. But
changing it is _still_ going to break people's code that switches on what
were, previously, the only possible error codes that could be returned
during a shutdown -- which didn't include WANT_READ and WANT_WRITE.
I can easily fix the code _I_ care about to conform to the (better) API
you're proposing. But I don't think that's a particularly good reason to
break other people's code, and pretending that it was impossible to get
the job done isn't tremendously helpful either; there really is a lot of
code out there already that uses non-blocking BIOs despite all their
warts (see my complaints about the need for SSL_select() from several
months ago for another example) and that code really, truly does manage
to shut down sessions without spinning.
Thor
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