[PATCH v2 10/16] target_terminal::ours_for_output before printing signal received

[Pedro Alves <pedro@palves.net>]

A following patch will make GDB put spawned inferiors in their own
terminal/session (on GNU/Linux).  In that case, GDB is in control of
when is the inferior's output flushed to the screen.  A sync point is
when target_terminal state goes from inferior -> ours/ours_for_output.

The gdb.multi/multi-term-settings.exp testcase exposed a bug where an
inferior output flush is missing, resulting in this regression:

Good:

 (gdb) PASS: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: info inferiors
 continue
 Continuing.
 pid=1275538, count=0
 pid=1276069, count=0

 Thread 1.1 "multi-term-sett" received signal SIGTTOU, Stopped (tty output).
 [Switching to process 1275538]
 0x00007ffff7ecda14 in __tcsetattr (fd=0, optional_actions=0, termios_p=0x7fffffffd450) at ../sysdeps/unix/sysv/linux/tcsetattr.c:83
 83	../sysdeps/unix/sysv/linux/tcsetattr.c: No such file or directory.
 (gdb) PASS: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: continue (expected SIGTTOU)
 Quit
 (gdb) PASS: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: stop with control-c (Quit)

Bad:

 (gdb) PASS: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: info inferiors
 continue
 Continuing.
 pid=1287638, count=0

 Thread 1.1 "multi-term-sett" received signal SIGTTOU, Stopped (tty output).
 pid=1287663, count=0                      <<<<<< HERE
 [Switching to process 1287638]
 0x00007ffff7ecda14 in __tcsetattr (fd=0, optional_actions=0, termios_p=0x7fffffffd450) at ../sysdeps/unix/sysv/linux/tcsetattr.c:83
 83	../sysdeps/unix/sysv/linux/tcsetattr.c: No such file or directory.
 (gdb) FAIL: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: continue
 Quit
 (gdb) PASS: gdb.multi/multi-term-settings.exp: inf1_how=run-share: inf2_how=run-session: stop with control-c (Quit)


Notice the "<<<<<< HERE" line in the "Bad" output above -- that is
inferior output being printed on the screen _after_ GDB says the
thread stopped...  That's obviously bogus, the output was printed by
the inferior before it was stopped.

The fix is to claim back the terminal for output before printing the
"signal received SIGTTOU" message.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* infrun.c (normal_stop): Call target_terminal::ours_for_output
	before calling signal_received observers.

Change-Id: Iea106c33b4c585562fc3579ca85d43481fa214f0
---
 gdb/infrun.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4bd21fde590..1eb7526d246 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -8537,7 +8537,10 @@ normal_stop (void)
   update_thread_list ();
 
   if (last.kind == TARGET_WAITKIND_STOPPED && stopped_by_random_signal)
-    gdb::observers::signal_received.notify (inferior_thread ()->suspend.stop_signal);
+    {
+      target_terminal::ours_for_output ();
+      gdb::observers::signal_received.notify (inferior_thread ()->suspend.stop_signal);
+    }
 
   /* As with the notification of thread events, we want to delay
      notifying the user that we've switched thread context until
-- 
2.26.2