bug#56487: xgselect race condition leading to abort when USE_GTK not defined

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Tom Gillespie <tgbugs@gmail.com> writes:

> -#ifdef USE_GTK
>    bool already_has_events;
> -#endif
>  
>    if (xg_select_suppress_count)
>      return pselect (fds_lim, rfds, wfds, efds, timeout, sigmask);
> @@ -126,8 +132,8 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
>    context = g_main_context_default ();
>    acquire_select_lock (context);
>  
> -#ifdef USE_GTK
>    already_has_events = g_main_context_pending (context);
> +#ifdef USE_GTK
>  #ifndef HAVE_PGTK
>    already_has_events = already_has_events && x_gtk_use_native_input;
>  #endif
> @@ -179,12 +185,6 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
>  	tmop = &tmo;
>      }
>  
> -#ifndef USE_GTK
> -  fds_lim = max_fds + 1;
> -  nfds = thread_select (pselect, fds_lim,
> -			&all_rfds, have_wfds ? &all_wfds : NULL, efds,
> -			tmop, sigmask);
> -#else
>    /* On PGTK, when you type a key, the key press event are received,
>       and one more key press event seems to be received internally.
>  
> @@ -217,7 +217,6 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
>  	FD_ZERO (efds);
>        our_fds++;
>      }
> -#endif
>  
>    if (nfds < 0)
>      retval = nfds;
> @@ -248,11 +247,7 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
>  
>    /* If Gtk+ is in use eventually gtk_main_iteration will be called,
>       unless retval is zero.  */
> -#ifdef USE_GTK
>    need_to_dispatch = retval == 0;
> -#else
> -  need_to_dispatch = true;
> -#endif
>  
>    /* xwidgets make heavy use of GLib subprocesses, which add their own
>       SIGCHLD handler at arbitrary locations.  That doesn't play well

Thanks.  Why did the code previously under !USE_GTK have to be removed?