[RFA 02/22] Use RAII to save and restore scalars

[Tom Tromey <tom at tromey dot com>]

This patch replaces many (but not all) uses of
make_cleanup_restore_integer with a simple RAII-based template class.
It also removes the similar restore_execution_direction cleanup in
favor of this new class.  Subsequent patches will replace other
similar cleanups with this class.

I chose the name "scoped_restore" for this class.  I considered that
perhaps "auto_restore" might be clearer.  Or maybe something else;
it's simple enough to change.

I had hoped that template parameter deduction would work here, but it
did not, and so the patch uses explicit template parameters
everywhere.

2016-09-26  Tom Tromey  <tom@tromey.com>

	* utils.h (class scoped_restore): New class.
	* top.c (execute_command_to_string): Use scoped_restore.
	* python/python.c (python_interactive_command): Use
	scoped_restore.
	(python_command, execute_gdb_command): Likewise.
	* printcmd.c (do_one_display): Use scoped_restore.
	* mi/mi-main.c (exec_continue): Use scoped_restore.
	* mi/mi-cmd-var.c (mi_cmd_var_assign): Use scoped_restore.
	* linux-fork.c (checkpoint_command): Use scoped_restore.
	* infrun.c (restore_execution_direction): Remove.
	(fetch_inferior_event): Use scoped_restore.
	* compile/compile.c (compile_file_command): Use
	scoped_restore.
	(compile_code_command, compile_print_command): Likewise.
	* cli/cli-script.c (execute_user_command): Use
	scoped_restore.
	(while_command, if_command, script_from_file): Likewise.
	* arm-tdep.c (arm_insert_single_step_breakpoint): Use
	scoped_restore.
---
 gdb/ChangeLog         | 22 ++++++++++++++++++++++
 gdb/arm-tdep.c        |  8 ++------
 gdb/cli/cli-script.c  | 18 ++++--------------
 gdb/compile/compile.c | 23 ++++++++---------------
 gdb/infrun.c          | 16 ++--------------
 gdb/linux-fork.c      | 11 ++++++-----
 gdb/mi/mi-cmd-var.c   |  7 +------
 gdb/mi/mi-main.c      |  3 +--
 gdb/printcmd.c        |  5 +----
 gdb/python/python.c   | 12 +++---------
 gdb/top.c             |  3 +--
 gdb/utils.h           | 44 ++++++++++++++++++++++++++++++++++++++++++++
 12 files changed, 95 insertions(+), 77 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2f28e54..104048f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,27 @@
 2016-09-26  Tom Tromey  <tom@tromey.com>
 
+	* utils.h (class scoped_restore): New class.
+	* top.c (execute_command_to_string): Use scoped_restore.
+	* python/python.c (python_interactive_command): Use
+	scoped_restore.
+	(python_command, execute_gdb_command): Likewise.
+	* printcmd.c (do_one_display): Use scoped_restore.
+	* mi/mi-main.c (exec_continue): Use scoped_restore.
+	* mi/mi-cmd-var.c (mi_cmd_var_assign): Use scoped_restore.
+	* linux-fork.c (checkpoint_command): Use scoped_restore.
+	* infrun.c (restore_execution_direction): Remove.
+	(fetch_inferior_event): Use scoped_restore.
+	* compile/compile.c (compile_file_command): Use
+	scoped_restore.
+	(compile_code_command, compile_print_command): Likewise.
+	* cli/cli-script.c (execute_user_command): Use
+	scoped_restore.
+	(while_command, if_command, script_from_file): Likewise.
+	* arm-tdep.c (arm_insert_single_step_breakpoint): Use
+	scoped_restore.
+
+2016-09-26  Tom Tromey  <tom@tromey.com>
+
 	* selftest.c: Include <vector>, not "vec.h".
 	(self_test_function_ptr): Remove.
 	(tests): Now a std::vector.
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 4dfd76b..d7a8799 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -4205,15 +4205,11 @@ arm_insert_single_step_breakpoint (struct gdbarch *gdbarch,
 				   struct address_space *aspace,
 				   CORE_ADDR pc)
 {
-  struct cleanup *old_chain
-    = make_cleanup_restore_integer (&arm_override_mode);
-
-  arm_override_mode = IS_THUMB_ADDR (pc);
+  scoped_restore<int> save_override_mode (&arm_override_mode,
+					  IS_THUMB_ADDR (pc));
   pc = gdbarch_addr_bits_remove (gdbarch, pc);
 
   insert_single_step_breakpoint (gdbarch, aspace, pc);
-
-  do_cleanups (old_chain);
 }
 
 /* Given BUF, which is OLD_LEN bytes ending at ENDADDR, expand
diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index 579d0a4..bf18226 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -380,8 +380,7 @@ execute_user_command (struct cmd_list_element *c, char *args)
      not confused with Insight.  */
   in_user_command = 1;
 
-  make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   command_nest_depth++;
   while (cmdlines)
@@ -654,7 +653,6 @@ static void
 while_command (char *arg, int from_tty)
 {
   struct command_line *command = NULL;
-  struct cleanup *old_chain;
 
   control_level = 1;
   command = get_command_line (while_control, arg);
@@ -662,13 +660,10 @@ while_command (char *arg, int from_tty)
   if (command == NULL)
     return;
 
-  old_chain = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   execute_control_command_untraced (command);
   free_command_lines (&command);
-
-  do_cleanups (old_chain);
 }
 
 /* "if" command support.  Execute either the true or false arm depending
@@ -686,13 +681,10 @@ if_command (char *arg, int from_tty)
   if (command == NULL)
     return;
 
-  old_chain = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   execute_control_command_untraced (command);
   free_command_lines (&command);
-
-  do_cleanups (old_chain);
 }
 
 /* Cleanup */
@@ -1693,10 +1685,8 @@ script_from_file (FILE *stream, const char *file)
   source_line_number = 0;
   source_file_name = file;
 
-  make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
-
   {
+    scoped_restore<int> save_async (&current_ui->async, 0);
 
     TRY
       {
diff --git a/gdb/compile/compile.c b/gdb/compile/compile.c
index 0c4a738..e2be115 100644
--- a/gdb/compile/compile.c
+++ b/gdb/compile/compile.c
@@ -91,8 +91,7 @@ compile_file_command (char *arg, int from_tty)
   char *buffer;
   struct cleanup *cleanup;
 
-  cleanup = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   /* Check the user did not just <enter> after command.  */
   if (arg == NULL)
@@ -115,7 +114,7 @@ compile_file_command (char *arg, int from_tty)
 
   arg = skip_spaces (arg);
   arg = gdb_abspath (arg);
-  make_cleanup (xfree, arg);
+  cleanup = make_cleanup (xfree, arg);
   buffer = xstrprintf ("#include \"%s\"\n", arg);
   make_cleanup (xfree, buffer);
   eval_compile_command (NULL, buffer, scope, NULL);
@@ -130,11 +129,9 @@ compile_file_command (char *arg, int from_tty)
 static void
 compile_code_command (char *arg, int from_tty)
 {
-  struct cleanup *cleanup;
   enum compile_i_scope_types scope = COMPILE_I_SIMPLE_SCOPE;
 
-  cleanup = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   if (arg != NULL && check_raw_argument (&arg))
     {
@@ -155,13 +152,12 @@ compile_code_command (char *arg, int from_tty)
   else
     {
       struct command_line *l = get_command_line (compile_control, "");
+      struct cleanup *cleanup = make_cleanup_free_command_lines (&l);
 
-      make_cleanup_free_command_lines (&l);
       l->control_u.compile.scope = scope;
       execute_control_command_untraced (l);
+      do_cleanups (cleanup);
     }
-
-  do_cleanups (cleanup);
 }
 
 /* Callback for compile_print_command.  */
@@ -183,12 +179,10 @@ static void
 compile_print_command (char *arg_param, int from_tty)
 {
   const char *arg = arg_param;
-  struct cleanup *cleanup;
   enum compile_i_scope_types scope = COMPILE_I_PRINT_ADDRESS_SCOPE;
   struct format_data fmt;
 
-  cleanup = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   /* Passing &FMT as SCOPE_DATA is safe as do_module_cleanup will not
      touch the stale pointer if compile_object_run has already quit.  */
@@ -199,14 +193,13 @@ compile_print_command (char *arg_param, int from_tty)
   else
     {
       struct command_line *l = get_command_line (compile_control, "");
+      struct cleanup *cleanup = make_cleanup_free_command_lines (&l);
 
-      make_cleanup_free_command_lines (&l);
       l->control_u.compile.scope = scope;
       l->control_u.compile.scope_data = &fmt;
       execute_control_command_untraced (l);
+      do_cleanups (cleanup);
     }
-
-  do_cleanups (cleanup);
 }
 
 /* A cleanup function to remove a directory and all its contents.  */
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 2636a19..7832a5d 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -3879,17 +3879,6 @@ all_uis_on_sync_execution_starting (void)
     }
 }
 
-/* A cleanup that restores the execution direction to the value saved
-   in *ARG.  */
-
-static void
-restore_execution_direction (void *arg)
-{
-  enum exec_direction_kind *save_exec_dir = (enum exec_direction_kind *) arg;
-
-  execution_direction = *save_exec_dir;
-}
-
 /* Asynchronous version of wait_for_inferior.  It is called by the
    event loop whenever a change of state is detected on the file
    descriptor corresponding to the target.  It can be called more than
@@ -3906,7 +3895,6 @@ fetch_inferior_event (void *client_data)
   struct execution_control_state *ecs = &ecss;
   struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
   struct cleanup *ts_old_chain;
-  enum exec_direction_kind save_exec_dir = execution_direction;
   int cmd_done = 0;
   ptid_t waiton_ptid = minus_one_ptid;
 
@@ -3945,8 +3933,8 @@ fetch_inferior_event (void *client_data)
      event.  */
   target_dcache_invalidate ();
 
-  make_cleanup (restore_execution_direction, &save_exec_dir);
-  execution_direction = target_execution_direction ();
+  scoped_restore<enum exec_direction_kind>
+    save_exec_dir (&execution_direction, target_execution_direction ());
 
   ecs->ptid = do_target_wait (waiton_ptid, &ecs->ws,
 			      target_can_async_p () ? TARGET_WNOHANG : 0);
diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index e7202dd..9c2cf8a 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -680,7 +680,6 @@ checkpoint_command (char *args, int from_tty)
   struct value *fork_fn = NULL, *ret;
   struct fork_info *fp;
   pid_t retpid;
-  struct cleanup *old_chain;
 
   if (!target_has_execution) 
     error (_("The program is not being run."));
@@ -704,11 +703,13 @@ checkpoint_command (char *args, int from_tty)
   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 
   /* Tell linux-nat.c that we're checkpointing this inferior.  */
-  old_chain = make_cleanup_restore_integer (&checkpointing_pid);
-  checkpointing_pid = ptid_get_pid (inferior_ptid);
+  {
+    scoped_restore<int> save_pid (&checkpointing_pid,
+				  ptid_get_pid (inferior_ptid));
+
+    ret = call_function_by_hand (fork_fn, 0, &ret);
+  }
 
-  ret = call_function_by_hand (fork_fn, 0, &ret);
-  do_cleanups (old_chain);
   if (!ret)	/* Probably can't happen.  */
     error (_("checkpoint: call_function_by_hand returned null."));
 
diff --git a/gdb/mi/mi-cmd-var.c b/gdb/mi/mi-cmd-var.c
index 3bfe4f0..1c78104 100644
--- a/gdb/mi/mi-cmd-var.c
+++ b/gdb/mi/mi-cmd-var.c
@@ -608,7 +608,6 @@ mi_cmd_var_assign (char *command, char **argv, int argc)
   struct ui_out *uiout = current_uiout;
   struct varobj *var;
   char *expression, *val;
-  struct cleanup *cleanup;
 
   if (argc != 2)
     error (_("-var-assign: Usage: NAME EXPRESSION."));
@@ -623,9 +622,7 @@ mi_cmd_var_assign (char *command, char **argv, int argc)
 
   /* MI command '-var-assign' may write memory, so suppress memory
      changed notification if it does.  */
-  cleanup
-    = make_cleanup_restore_integer (&mi_suppress_notification.memory);
-  mi_suppress_notification.memory = 1;
+  scoped_restore<int> save_suppress (&mi_suppress_notification.memory, 1);
 
   if (!varobj_set_value (var, expression))
     error (_("-var-assign: Could not assign "
@@ -634,8 +631,6 @@ mi_cmd_var_assign (char *command, char **argv, int argc)
   val = varobj_get_value (var);
   ui_out_field_string (uiout, "value", val);
   xfree (val);
-
-  do_cleanups (cleanup);
 }
 
 /* Type used for parameters passing to mi_cmd_var_update_iter.  */
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 1913157..c6c7067 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -300,7 +300,7 @@ exec_continue (char **argv, int argc)
     }
   else
     {
-      struct cleanup *back_to = make_cleanup_restore_integer (&sched_multi);
+      scoped_restore<int> save_multi (&sched_multi);
 
       if (current_context->all)
 	{
@@ -315,7 +315,6 @@ exec_continue (char **argv, int argc)
 	     same.  */
 	  continue_1 (1);
 	}
-      do_cleanups (back_to);
     }
 }
 
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index d4a4b9e..1fccd26 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -1938,7 +1938,6 @@ undisplay_command (char *args, int from_tty)
 static void
 do_one_display (struct display *d)
 {
-  struct cleanup *old_chain;
   int within_current_scope;
 
   if (d->enabled_p == 0)
@@ -1990,8 +1989,7 @@ do_one_display (struct display *d)
   if (!within_current_scope)
     return;
 
-  old_chain = make_cleanup_restore_integer (&current_display_number);
-  current_display_number = d->number;
+  scoped_restore<int> save_display_number (&current_display_number, d->number);
 
   annotate_display_begin ();
   printf_filtered ("%d", d->number);
@@ -2079,7 +2077,6 @@ do_one_display (struct display *d)
   annotate_display_end ();
 
   gdb_flush (gdb_stdout);
-  do_cleanups (old_chain);
 }
 
 /* Display all of the values on the auto-display chain which can be
diff --git a/gdb/python/python.c b/gdb/python/python.c
index b00b70b..9e4d610 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -319,11 +319,9 @@ static void
 python_interactive_command (char *arg, int from_tty)
 {
   struct ui *ui = current_ui;
-  struct cleanup *cleanup;
   int err;
 
-  cleanup = make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   arg = skip_spaces (arg);
 
@@ -351,8 +349,6 @@ python_interactive_command (char *arg, int from_tty)
       gdbpy_print_stack ();
       error (_("Error while executing Python code."));
     }
-
-  do_cleanups (cleanup);
 }
 
 /* A wrapper around PyRun_SimpleFile.  FILE is the Python script to run
@@ -467,8 +463,7 @@ python_command (char *arg, int from_tty)
 
   cleanup = ensure_python_env (get_current_arch (), current_language);
 
-  make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   arg = skip_spaces (arg);
   if (arg && *arg)
@@ -651,8 +646,7 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
       struct cleanup *cleanup = make_cleanup (xfree, copy);
       struct interp *interp;
 
-      make_cleanup_restore_integer (&current_ui->async);
-      current_ui->async = 0;
+      scoped_restore<int> save_async (&current_ui->async, 0);
 
       make_cleanup_restore_current_uiout ();
 
diff --git a/gdb/top.c b/gdb/top.c
index 3cfa113..84285b2 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -701,8 +701,7 @@ execute_command_to_string (char *p, int from_tty)
      restoration callbacks.  */
   cleanup = set_batch_flag_and_make_cleanup_restore_page_info ();
 
-  make_cleanup_restore_integer (&current_ui->async);
-  current_ui->async = 0;
+  scoped_restore<int> save_async (&current_ui->async, 0);
 
   str_file = mem_fileopen ();
 
diff --git a/gdb/utils.h b/gdb/utils.h
index 8635075..63583ed 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -84,6 +84,50 @@ extern struct cleanup *make_cleanup_bfd_unref (bfd *abfd);
 struct obstack;
 extern struct cleanup *make_cleanup_obstack_free (struct obstack *obstack);
 
+// An RAII-based object that saves a variable's value, and then
+// restores it again when this object is destroyed.
+template<typename T>
+class scoped_restore
+{
+ public:
+
+  // Create a new scoped_restore object that saves the current value
+  // of *VAR, and then sets *VAR to VALUE.  *VAR will be restored when
+  // this scoped_restore object is destroyed.
+  scoped_restore (T *var, T value)
+    : saved_var (var),
+      saved_value (*var)
+  {
+    *var = value;
+  }
+
+  // Create a new scoped_restore object that saves the current value
+  // of *VAR.  *VAR will be restored when this scoped_restore object
+  // is destroyed.
+  explicit scoped_restore (T *var)
+    : saved_var (var),
+      saved_value (*var)
+  {
+  }
+
+  ~scoped_restore ()
+  {
+    *saved_var = saved_value;
+  }
+
+ private:
+
+  // No need for these.  They are intentionally not defined anywhere.
+  scoped_restore &operator= (const scoped_restore &);
+  scoped_restore (const scoped_restore &);
+
+  // The saved variable.
+  T *saved_var;
+
+  // The saved value.
+  T saved_value;
+};
+
 extern struct cleanup *make_cleanup_restore_integer (int *variable);
 extern struct cleanup *make_cleanup_restore_uinteger (unsigned int *variable);
 
-- 
2.7.4