Re: g_io_add_watch() callback called constantly

[Gnaural <gnaural users sourceforge net>]

Thanks for the reply, this helps because I got the
(mis)impression from the docs that
g_io_channel_new_file() was the best cross platform
approach... but I didn't really realize it really was
just a plain "fopen()" file! I guess I thought is was
a "magic" file :-)

But it was a fun investigation -- my goofy little test
server/client is below, as requested. And it does sort
of work! Like tin cans and string...

But sockets do seem the right solution. Ironically, I
first thought to use them a month ago... but to avoid
maintaining separate platform code, I first tried
dbus-glib, then hacked a cross-compilable solution in
low-level dbus... which ran great in windows, but
because of my crude implementation, went haywire in
Linux with any call to gtk_file_chooser_dialog_new()!

So now I'm back to sockets. Thanks again.

--- Tor Lillqvist <tml iki fi> wrote:
> I wrote:
> > What is it that you create the GIOChannel for?
> 
> Ah, you said it yourself, g_iochannel_new_file(), so
> for a plain file
> presumably. You mean that the processes take turns
> appending their
> "messages" to the file, and the other process then
> reads it from the
> file, and then appends its own "reply"?
> 
> I am not sure using watched GIOChannels connected to
> plain files for
> inter-process communication is necessarily something
> that has been
> tested at all, especially not on Windows. It sounds
> like a quite, eh,
> unique idea. I don't know if there even exists any
> mechanism on
> Windows that would enable the kind of select() or
> poll() functionality
> that presumably works fine also for plain files on
> Unix. You might
> have better luck using pipes or sockets like more or
> less everybody
> else.
> 
> --tml

/*
Client: 
Sends a struct with an ID and a double.
Compile:
gcc `pkg-config --libs --cflags gtk+-2.0` \
client.c -o GIOChannel-server
 */
#include <glib.h>
#include <gtk/gtk.h>

struct
{
 char ID;
 double Value;
} message;
const gssize message_size =
 sizeof (message);

int main (int argc, char **argv)
{
 char a;
 gsize written = 0;
 GError *error = NULL;
 gchar *filename =
  g_strconcat (g_get_tmp_dir (),
	       G_DIR_SEPARATOR_S,
	       "MyTempFile", NULL);
 GIOChannel *ioch =
  g_io_channel_new_file (filename, "a+",
			 &error);

 g_print ("filename:\%s\n", filename);
 g_free (filename);

 if (G_IO_STATUS_NORMAL ==
     g_io_channel_set_encoding (ioch,
				NULL,
				NULL))
  g_print
   ("Port initialization success\n");
 else
  g_print ("Not right\n");
 for (a = 'a'; a <= 'z'; a++)
 {
  message.ID = a;
  message.Value = a;
  g_io_channel_seek_position (ioch, 0,
			      G_SEEK_SET,
			      &error);
  g_io_channel_write_chars (ioch,
			    (gchar *) &
			    message,
			    message_size,
			    &written,
			    &error);
  g_io_channel_flush (ioch, &error);
  g_usleep (100000);
 }
 g_io_channel_flush (ioch, &error);
 g_io_channel_shutdown (ioch, TRUE,
			&error);
 g_io_channel_unref (ioch);
 return 0;
}

//===============

/*
Server:
Recieves a struct with an ID and a double
Compile:
gcc `pkg-config --libs --cflags gtk+-2.0` \
server.c -o GIOChannel-server
 */
#include <gtk/gtk.h>

struct
{
 char ID;
 double Value;
} message;
const gssize message_size =
 sizeof (message);

gboolean io_callback (GIOChannel * ioch,
		      GIOCondition cond,
		      gpointer data)
{
 gsize bytes_read;
 static int count = 0;

 do
 {
  g_io_channel_read_chars (ioch,
			   (gchar *) &
			   message,
			   message_size,
			   &bytes_read,
			   NULL);
  if (message_size == bytes_read)
  {
   g_print ("\nID: %d, Value: %g",
	    message.ID, message.Value);
  }
  else
   g_print (".");
 }
 while (bytes_read);
 g_usleep (100000);

 if (50 < ++count)
  gtk_main_quit ();
 return TRUE;
}

int main (int argc, char **argv)
{
 GError *error = NULL;
 gchar *filename =
  g_strconcat (g_get_tmp_dir (),
	       G_DIR_SEPARATOR_S,
	       "MyTempFile", NULL);
 GIOChannel *ioch =
  g_io_channel_new_file (filename, "w+",
			 &error);

 g_type_init ();
 g_print ("filename:\%s\n", filename);
 g_free (filename);

 if (G_IO_STATUS_NORMAL ==
     g_io_channel_set_encoding (ioch,
				NULL,
				NULL))
  g_print
   ("File initialization success\n");
 else
  g_print
   ("File initialization failure\n");
 guint iowatch =
  g_io_add_watch (ioch, G_IO_IN,
		  io_callback, NULL);

 if (0 == iowatch)
  g_error ("Error creating watch\n");
 gtk_main ();
 g_source_remove (iowatch);
 g_io_channel_shutdown (ioch, TRUE,
			&error);
 g_io_channel_unref (ioch);
 return 0;
}