poll(2) only can handle 256 fds?

[Markus Lausser <sgop users sourceforge net>]

On Tue, 2005-03-08 at 21:56, Markus Lausser wrote:
> Hello,
>
> i get the message
>   *** GLib *** : poll(2) failed due to: Invalid argument.
> thousand times when running my application.
> It seems that it happens if i have accepted 100 < x < 200
> tcp connection from which i listen for input.
>
> What can i do? I am using glib 2.6.0 on a linux system.

I've did some investigation, and it appears that glib runs into
an endless loop when it tries to poll more than 256 fds at once.

I've written a short test program which reproduces this behaviour
on my system. Can anyone verify this?

The Program:
------------
#include <stdlib.h>
#include <glib.h>

static GMainLoop* MainLoop = NULL;

static gboolean
io_invoke(GIOChannel* source, GIOCondition condition,
          gpointer data) {
  int* num = data;
  (void)source;
  (void)condition;
  g_log("TEST", G_LOG_LEVEL_DEBUG, "io invoke called %d", *num);
  *num = *num-1;
  return FALSE;
}

static gboolean add_channels(int* num) {
  int i1;
  g_log("TEST", G_LOG_LEVEL_DEBUG, "adding %d channels", *num);
  for (i1 = 0; i1 < *num; i1++) {
    GIOChannel* channel = g_io_channel_unix_new(0);
    g_io_add_watch_full(channel, G_PRIORITY_DEFAULT, 
                        G_IO_IN | G_IO_HUP | G_IO_ERR,
                        io_invoke, num, NULL);
  }
  return FALSE;
}

static gboolean end_program() {
  g_log("TEST", G_LOG_LEVEL_DEBUG, "ending program");
  g_main_loop_quit(MainLoop);
  return FALSE;
}

int main(int argc, char** argv) {
  int num;

  if (argc != 2) {
    g_log("TEST", G_LOG_LEVEL_WARNING,
          "one integer argument required");
    return -1;
  }
  num = atoi(argv[1]);

  MainLoop = g_main_loop_new(NULL, FALSE);

  g_timeout_add(1000, (GSourceFunc)add_channels, &num);
  g_timeout_add(10000, (GSourceFunc)end_program, NULL);
  
  g_main_loop_run(MainLoop);

  return 0;
}
-------------
Compile:
$ gcc -Wall `pkg-config --cflags --libs glib-2.0` main.c -o test

run without problems: ./test 256
run with endless loop: ./test 257


Markus.