Use ui_out_emit_table and ui_out_emit_list in print_thread_info_1

This changes print_thread_info_1 to use ui_out_emit_table and
ui_out_emit_list.  Which one is used depends on whether the ui-out is
mi-like; so the emitters are wrapped in gdb::optional.

ChangeLog
2017-09-09  Tom Tromey  <tom@tromey.com>

	* thread.c (print_thread_info_1): Use ui_out_emit_table,
	ui_out_emit_list, gdb::optional.

2 files changed, 51 insertions, 46 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ae6f2c9e414..0078d2e0448 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-09  Tom Tromey  <tom@tromey.com>
+
+	* thread.c (print_thread_info_1): Use ui_out_emit_table,
+	ui_out_emit_list, gdb::optional.
+
 2017-09-09  John Baldwin  <jhb@FreeBSD.org>
 
 	* aarch64-linux-nat.c: Remove _initialize_aarch64_linux_nat
diff --git a/gdb/thread.c b/gdb/thread.c
index 2185d505a3f..af7900df5ca 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -45,6 +45,7 @@
 #include "thread-fsm.h"
 #include "tid-parse.h"
 #include <algorithm>
+#include "common/gdb_optional.h"
 
 /* Definition of struct thread_info exported to gdbthread.h.  */
 
@@ -1243,55 +1244,55 @@ print_thread_info_1 (struct ui_out *uiout, char *requested_threads,
   update_thread_list ();
   current_ptid = inferior_ptid;
 
-  struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
-
-  /* For backward compatibility, we make a list for MI.  A table is
-     preferable for the CLI, though, because it shows table
-     headers.  */
-  if (uiout->is_mi_like_p ())
-    make_cleanup_ui_out_list_begin_end (uiout, "threads");
-  else
-    {
-      int n_threads = 0;
+  {
+    /* For backward compatibility, we make a list for MI.  A table is
+       preferable for the CLI, though, because it shows table
+       headers.  */
+    gdb::optional<ui_out_emit_list> list_emitter;
+    gdb::optional<ui_out_emit_table> table_emitter;
+
+    if (uiout->is_mi_like_p ())
+      list_emitter.emplace (uiout, "threads");
+    else
+      {
+	int n_threads = 0;
 
-      for (tp = thread_list; tp; tp = tp->next)
-	{
-	  if (!should_print_thread (requested_threads, default_inf_num,
-				    global_ids, pid, tp))
-	    continue;
+	for (tp = thread_list; tp; tp = tp->next)
+	  {
+	    if (!should_print_thread (requested_threads, default_inf_num,
+				      global_ids, pid, tp))
+	      continue;
 
-	  ++n_threads;
-	}
+	    ++n_threads;
+	  }
 
-      if (n_threads == 0)
-	{
-	  if (requested_threads == NULL || *requested_threads == '\0')
-	    uiout->message (_("No threads.\n"));
-	  else
-	    uiout->message (_("No threads match '%s'.\n"),
-			    requested_threads);
-	  do_cleanups (old_chain);
-	  return;
-	}
+	if (n_threads == 0)
+	  {
+	    if (requested_threads == NULL || *requested_threads == '\0')
+	      uiout->message (_("No threads.\n"));
+	    else
+	      uiout->message (_("No threads match '%s'.\n"),
+			      requested_threads);
+	    return;
+	  }
 
-      if (show_global_ids || uiout->is_mi_like_p ())
-	make_cleanup_ui_out_table_begin_end (uiout, 5, n_threads, "threads");
-      else
-	make_cleanup_ui_out_table_begin_end (uiout, 4, n_threads, "threads");
+	table_emitter.emplace (uiout,
+			       (show_global_ids || uiout->is_mi_like_p ())
+			       ? 5 : 4,
+			       n_threads, "threads");
 
-      uiout->table_header (1, ui_left, "current", "");
+	uiout->table_header (1, ui_left, "current", "");
 
-      if (!uiout->is_mi_like_p ())
-	uiout->table_header (4, ui_left, "id-in-tg", "Id");
-      if (show_global_ids || uiout->is_mi_like_p ())
-	uiout->table_header (4, ui_left, "id", "GId");
-      uiout->table_header (17, ui_left, "target-id", "Target Id");
-      uiout->table_header (1, ui_left, "frame", "Frame");
-      uiout->table_body ();
-    }
+	if (!uiout->is_mi_like_p ())
+	  uiout->table_header (4, ui_left, "id-in-tg", "Id");
+	if (show_global_ids || uiout->is_mi_like_p ())
+	  uiout->table_header (4, ui_left, "id", "GId");
+	uiout->table_header (17, ui_left, "target-id", "Target Id");
+	uiout->table_header (1, ui_left, "frame", "Frame");
+	uiout->table_body ();
+      }
 
-  /* We'll be switching threads temporarily.  */
-  {
+    /* We'll be switching threads temporarily.  */
     scoped_restore_current_thread restore_thread;
 
     ALL_THREADS_BY_INFERIOR (inf, tp)
@@ -1379,14 +1380,13 @@ print_thread_info_1 (struct ui_out *uiout, char *requested_threads,
 	core = target_core_of_thread (tp->ptid);
 	if (uiout->is_mi_like_p () && core != -1)
 	  uiout->field_int ("core", core);
-    }
+      }
 
     /* This end scope restores the current thread and the frame
-       selected before the "info threads" command.  */
+       selected before the "info threads" command, and it finishes the
+       ui-out list or table.  */
   }
 
-  do_cleanups (old_chain);
-
   if (pid == -1 && requested_threads == NULL)
     {
       if (uiout->is_mi_like_p ()