On Freitag, 27. November 2009, Erik Faye-Lund wrote:
> On Thu, Nov 26, 2009 at 10:53 PM, Johannes Sixt <j6t@xxxxxxxx> wrote:
> > On Donnerstag, 26. November 2009, Erik Faye-Lund wrote:
> >> @@ -327,7 +327,10 @@ int start_async(struct async *async)
> >> {
> >> int pipe_out[2];
> >>
> >> - if (pipe(pipe_out) < 0)
> >> + if (async->out) {
> >> + pipe_out[0] = dup(async->out);
> >> + pipe_out[1] = dup(async->out);
> >> + } else if (pipe(pipe_out) < 0)
> >> return error("cannot create pipe: %s", strerror(errno));
> >> async->out = pipe_out[0];
> >
> > Hm. If async->out != 0:
> >
> > pipe_out[0] = dup(async->out);
> > async->out = pipe_out[0];
> >
> > This is confusing.
>
> What do you find confusing about it? The idea is to use a provided
> bi-directional fd instead of a pipe if async->out is non-zero. The
> currently defined rules for async is that async->out must be zero
> (since the structure should be zero-initialized).
It is just the code structure that is confusing. It should be
if (async->out) {
/* fd was provided */
do all that is needed in this case
} else {
/* fd was requested */
do all for this other case
}
/* nothing to do anymore here */
(Of course, this should only replace the part that is cited above, not the
whole function.)
> > Moreover, you are assigning (a dup of) the same fd to the writable end.
> > This assumes a bi-directional channel. I don't yet know what I should
> > think about this (haven't studied the later patches, yet).
>
> Indeed it does. Do we want to extend it to support a set of
> unidirectional channels instead?
Yes, I think so. We could pass a regular int fd[2] array around with the clear
definition that both can be closed independently, i.e. one must be a dup() of
the other. struct async would also have such an array.
Speaking of dup(): The underlying function is DuplicateHandle(), and its
documentation says:
"You should not use DuplicateHandle to duplicate handles to the following
objects: ... o Sockets. ... use WSADuplicateSocket."
But then the docs of WSADuplicateSocket() talk only about duplicating a socket
to a separate process. Perhaps DuplicateHandle() of a socket within the same
process Just Works?
-- Hannes
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