static SCM
siscm_sigint_listener_thread (void *data)
{
  char c;
  int rc;
  sigset_t mask;

  /* Check SCM_USE_PTHREAD_THREADS to avoid compilation failures.
     This function will never get called if pthreads aren't available.  */
#if SCM_USE_PTHREAD_THREADS
  /*  Block most signals, certainly all async signals.  */
  sigfillset (&mask);
  sigdelset (&mask, SIGSEGV);
  sigdelset (&mask, SIGABRT);
  rc = pthread_sigmask (SIG_BLOCK, &mask, NULL);
#else
  rc = 0;
#endif
  if (rc != 0)
    {
      fprintf (stderr,
               "GDB/Guile SIGINT thread: Error setting signal mask: %s\n",
               safe_strerror (rc));
      return SCM_BOOL_F;
    }

  for (;;)
    {
      struct signal_pipe_data sigdata;

      scm_without_guile (read_signal_pipe_data, &sigdata);

      if (sigdata.n == 1)
        {
          if (siscm_sigint_mode_enabled)
            {
              scm_system_async_mark_for_thread (siscm_check_and_throw_sigint,
                                                siscm_main_thread);
            }
        }
      else
        {
          if (sigdata.n < 0)
            {
              gdbscm_printf (scm_current_error_port (),
                             "Error reading from SIGINT pipe: %s.\n",
                             safe_strerror (sigdata.err));
            }
          break;
        }
    }

  return SCM_BOOL_F;
}

Thread is spawned as:

  siscm_listener_thread = scm_spawn_thread (siscm_sigint_listener_thread, NULL,
                                            siscm_exception_catcher, NULL);