A GSource backed by timerfd. I'm not sure this is even useful, just a prototype.

g-interval-source.c

/* g-interval-source.c
 *
 * Copyright (C) 2013 Christian Hergert <christian@hergert.me>
 *
 * This file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This file is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/timerfd.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

#include "g-interval-source.h"

struct _GIntervalSource
{
   GSource source;
   GPollFD pollfd;
   struct itimerspec spec;
};

static gboolean
g_interval_source_prepare (GSource *source,
                           gint    *timeout_)
{
   GIntervalSource *isource = (GIntervalSource *)source;
   *timeout_ = -1;
   return !!isource->pollfd.revents;
}

static gboolean
g_interval_source_check (GSource *source)
{
   GIntervalSource *isource = (GIntervalSource *)source;
   return !!isource->pollfd.revents;
}

static gboolean
g_interval_source_dispatch (GSource     *source,
                            GSourceFunc  callback,
                            gpointer     user_data)
{
   GIntervalSource *isource = (GIntervalSource *)source;
   guint64 buf;

   if (isource->pollfd.fd != -1) {
      while (read(isource->pollfd.fd, &buf, sizeof buf) >= 8) {
         /* Do nothing */
      }
      isource->pollfd.revents = 0;
   }

   return callback ? callback(user_data) : TRUE;
}

static void
g_interval_source_finalize (GSource *source)
{
   GIntervalSource *isource = (GIntervalSource *)source;

   if (source) {
      g_source_remove_poll(source, &isource->pollfd);
      if (isource->pollfd.fd != -1) {
         close(isource->pollfd.fd);
         isource->pollfd.fd = -1;
      }
   }
}

static GSourceFuncs gSourceFuncs = {
   g_interval_source_prepare,
   g_interval_source_check,
   g_interval_source_dispatch,
   g_interval_source_finalize,
};

GSource *
g_interval_source_new (guint64 interval_msec)
{
   GIntervalSource *isource;
   GSource *source;
   int flags;
   int fd;

   source = g_source_new(&gSourceFuncs, sizeof(GIntervalSource));
   isource = (GIntervalSource *)source;

   memset(&isource->spec, 0, sizeof isource->spec);
   isource->spec.it_interval.tv_sec = interval_msec / 1000UL;
   isource->spec.it_interval.tv_nsec = (interval_msec % 1000UL) * 1000000UL;
   isource->spec.it_value.tv_nsec = 1;

   flags = TFD_NONBLOCK | TFD_CLOEXEC;

   errno = 0;
   if (-1 == (fd = timerfd_create(CLOCK_MONOTONIC, flags))) {
      g_warning("timerfd_create() faliure: %s", strerror(errno));
      g_source_destroy(source);
      return NULL;
   }

   errno = 0;
   if (-1 == timerfd_settime(fd, 0, &isource->spec, NULL)) {
      g_warning("timerfd_settime() failure: %s", strerror(errno));
      g_source_destroy(source);
      close(fd);
      return NULL;
   }

   isource->pollfd.fd = fd;
   isource->pollfd.events = G_IO_IN | G_IO_ERR;
   isource->pollfd.revents = 0;

   g_source_add_poll(source, &isource->pollfd);

   return source;
}

void
g_interval_source_pause (GIntervalSource *source)
{
   g_return_if_fail(source);
   source->spec.it_value.tv_nsec = 0;
}

void
g_interval_source_unpause (GIntervalSource *source)
{
   g_return_if_fail(source);
   source->spec.it_value.tv_nsec = 1;
}

g-interval-source.h

/* g-interval-source.h
 *
 * Copyright (C) 2013 Christian Hergert <christian@hergert.me>
 *
 * This file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This file is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef G_INTERVAL_SOURCE_H
#define G_INTERVAL_SOURCE_H

#include <glib.h>

G_BEGIN_DECLS

typedef struct _GIntervalSource GIntervalSource;

GSource *g_interval_source_new     (guint64 interval_msec);
void     g_interval_source_pause   (GIntervalSource *source);
void     g_interval_source_unpause (GIntervalSource *source);

G_END_DECLS

#endif /* G_INTERVAL_SOURCE_H */