Fix "resource temporarily unavailable" with xgselect.

* xgselect.c: Include <stdbool.h>.
(xg_select) [!USE_GTK]: Don't lose track of errno.

Fixes: debbugs:16925

src/ChangeLog

 2014-03-05  Paul Eggert  <eggert@cs.ucla.edu>
 
+	Fix "resource temporarily unavailable" with xgselect (Bug#16925).
+	* xgselect.c: Include <stdbool.h>.
+	(xg_select) [!USE_GTK]: Don't lose track of errno.
+
 	Fix minor --enable-gcc-warnings issues.
 	* widget.c (update_various_frame_slots, EmacsFrameResize):
 	Avoid unused locals.  Prefer 'if' to '#if' when either will do.

src/xgselect.c

@@ -25,6 +25,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <glib.h>
 #include <errno.h>
+#include <stdbool.h>
 #include <timespec.h>
 #include "frame.h"
 
@@ -43,6 +44,7 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
   int gfds_size = sizeof gfds_buf / sizeof *gfds_buf;
   int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
   int i, nfds, tmo_in_millisec;
+  bool need_to_dispatch;
   USE_SAFE_ALLOCA;
 
   /* Do not try to optimize with an initial check with g_main_context_pending
@@ -127,10 +129,17 @@ 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
-  if (retval == 0)
+  need_to_dispatch = retval == 0;
+#else
+  need_to_dispatch = true;
 #endif
-    while (g_main_context_pending (context))
-      g_main_context_dispatch (context);
+  if (need_to_dispatch)
+    {
+      int pselect_errno = errno;
+      while (g_main_context_pending (context))
+	g_main_context_dispatch (context);
+      errno = pselect_errno;
+    }
 
   /* To not have to recalculate timeout, return like this.  */
   if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))