On Wed, 20 Feb 2013 18:42:28 -0000
"William Orr" <ay1244 gmail com> wrote:
> Chris Vine wrote:
>
>
> On Tue, 19 Feb 2013 20:28:16 -0500
> Will Orr <ay1244 gmail com> wrote:
> > Here[1] is the problematic code.
> >
> > I'm trying to run a command and gather the output and return
> code. I
> > do this by watching for the process to return, as well as
> waiting for
> > the channels to HUP. However, my callbacks never get called with
> cond
> > set to G_IO_HUP, even after the process terminates. Nor do any
> of the
> > g_io_channel_read_* calls return errors. This seems inconsistent
> with
> > the documentation, as well as examples that I've found in the
> hours of
> > researching this problem.
> >
> > I'm clearly doing something wrong, I'm just not sure where yet.
> Any
> > advice or solutions would be great. Thanks so much! Let me know
> if I
> > need to provide anymore information. Please CC me, as I'm not a
> member
> > of this list.
>
> This will help you:
>
> http://www.greenend.org.uk/rjk/2001/06/poll.html
>
> Chris
>
> Is this really preferable to using g_io_add_watch? It doesn't seem
> like I can make use of that in my event loop…
I think you misunderstood me, and I can see that I was was overly
concise. g_poll() is a wrapper on unix-like OSes for poll(). The web
page to which I directed you explains why POLLHUP, and so G_IO_HUP, is
not a reliable indicator of end-of-file.
If you have received G_IO_HUP, you must have received a hang-up, which
means on a pipe file descriptor that you must have end-of-file. However
the converse is not true. You can have end-of-file without G_IO_HUP,
which is what you are experiencing. You are receiving POLLIN/G_IO_IN
instead.
The only reliable way of detecting end-of-file is if read() returns 0.
This equates to one of the GIOChannel read functions returning a
GIOStatus value of G_IO_STATUS_EOF. Your mistake was in not checking
return values.
I have not studied your code in detail but you do not seem to be
unref()ing consistently either, in particularly in a case of error. The
best thing to do is to unref() the GIOChannel object as soon as you have
called g_io_add_watch() or g_source_attach(). Then, returning FALSE in
the callback will automatically release the object and its resources.
Chris
