Re: watching a file descriptor in gtk3

[rbd <rbd soest hawaii edu>]

Hi Chris,

Thanks very much for all of that information -- it was very helpful!

> > I do not fully understand your question (especially I don't understand
> > your reference to using "g_idle_add_full() and do my own non-blocking
> > select() inside my callback", which would not work), ...

I won't be trying the above approach unless all else fails (see below), 
but I am curious as to why you say that I could not successfully call a 
non-blocking select() (or poll(), if you prefer) on my file descriptor of 
interest inside a callback registered via g_idle_add_full(), then read 
from that descriptor if select() tells me there's something there. This is 
not as logically sensible as registering a separate input source to be 
polled inside the main loop, but I can't see why it wouldn't work.

> > ... This may (or may not) help:
https://sourceforge.net/p/cxx-gtk-utils/git/ci/master/tree/c++-gtk-utils/io_$

Thanks very much for the above code sample -- unfortunately it confirms my 
very worst expectations of what might be involved with using 
g_source_add_unix_fd(), etc., to monitor a file descriptor, i.e., create a 
new GSource, code up a whole set of GSourceFuncs routines to implement a 
process which is not well-described in the docs, etc. I'm clearly barking 
up the wrong tree on that!

> > ...
https://developer.gnome.org/glib/stable/glib-IO-Channels.html#g-io-add-watch
> By the way, if you are thinking of using GIOChannel, you might also want
> to look at the implementation of gdk_input_add() and
> gdk_input_add_full() in gtk+-2. Although now deprecated in gtk+-2, you
> can still use those functions if you happen to be building against
> gtk+-2.

Using gtk3, not 2.

> If you are using gtk+3 you can set up a read watch as follows (I have
> not done a test compile on this snippet but it is what I have on
> occasions done in the past, and it avoids keeping an explicit GIOChannel
> object in scope if you only want to execute a callback when a
> descriptor is ready for input - you can use the internal reference
> counting to control channel lifetime):
>
>
> guint start_read_watch(int fd, GIOFunc func) {
>  GIOChannel *channel = g_io_channel_unix_new(fd);
>  guint id = g_io_add_watch(channel,
>                            G_IO_IN | G_IO_HUP | G_IO_ERR,
>                            func,
>                            NULL);

GIOChannel is the ticket, I think, thanks for pointing me there (where I 
would probably have never gotten on my own)! Unlike 
g_source_add_unix_fd(), of which I could find no useful example code 
whatsoever other than the code you sent me, there seem to be a fair number 
of examples around on basic use of GIOChannel to more or less do what I 
want to do (I hope). This 2005 Robert Love article in particular was quite 
useful:

http://www.linuxjournal.com/node/8545/print

Still not as drop-dead simple as libXt/Motif's XtAppAddInput() (and I 
cannot believe that I am actually favorably comparing Motif to any 
more contemporary API whatsoever ;-> ), but simple enough to be useful.

Thanks a bunch again, Chris!

Roger