Fix PR gdb/20418 - Problems with synchronous commands and new-ui

When executing commands on a secondary UI running the MI interpreter,
some commands that should be synchronous are not.  MI incorrectly
continues processing input right after the synchronous command is
sent, before the target stops.

The problem happens when we emit MI async events (=library-loaded,
etc.), and we go about restoring the previous terminal state, we end
up calling target_terminal_ours, which incorrectly always installs the
current UI's input_fd in the event loop...  That is, code like this:

   old_chain = make_cleanup_restore_target_terminal ();
   target_terminal_ours_for_output ();

   fprintf_unfiltered (mi->event_channel, "library-loaded");

...

   do_cleanups (old_chain);

The fix is to move the add_file_handler/delete_file_handler calls out
of target_terminal_$foo, making these completely no-ops unless called
with the main UI as current UI.

gdb/ChangeLog:
2016-08-09  Pedro Alves  <palves@redhat.com>

	PR gdb/20418
	* event-top.c (ui_register_input_event_handler)
	(ui_unregister_input_event_handler): New functions.
	(async_enable_stdin): Register input in the event loop.
	(async_disable_stdin): Unregister input from the event loop.
	(gdb_setup_readline): Register input in the event loop.
	* infrun.c (check_curr_ui_sync_execution_done): Register input in
	the event loop.
	* target.c (target_terminal_inferior): Don't unregister input from
	the event loop.
	(target_terminal_ours): Don't register input in the event loop.
	* target.h (target_terminal_inferior)
	(target_terminal_ours_for_output, target_terminal_ours): Update
	comments.
	* top.h (ui_register_input_event_handler)
	(ui_unregister_input_event_handler): New declarations.
	* utils.c (ui_unregister_input_event_handler_cleanup)
	(prepare_to_handle_input): New functions.
	(defaulted_query, prompt_for_continue): Use
	prepare_to_handle_input.

gdb/testsuite/ChangeLog:
2016-08-09  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@ericsson.com>

	PR gdb/20418
	* gdb.mi/new-ui-mi-sync.c, gdb.mi/new-ui-mi-sync.exp: New files.
	* lib/mi-support.exp (mi_expect_interrupt): Remove anchors.

1 files changed, 6 insertions, 0 deletions

diff --git a/gdb/top.h b/gdb/top.h
index bdc3529..c5f6bc7 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -191,6 +191,12 @@ extern struct cleanup *make_delete_ui_cleanup (struct ui *ui);
 /* Cleanup that restores the current UI.  */
 extern void restore_ui_cleanup (void *data);
 
+/* Register the UI's input file descriptor in the event loop.  */
+extern void ui_register_input_event_handler (struct ui *ui);
+
+/* Unregister the UI's input file descriptor from the event loop.  */
+extern void ui_unregister_input_event_handler (struct ui *ui);
+
 /* From top.c.  */
 extern char *saved_command_line;
 extern int in_user_command;