Re: [PATCH v4 1/1] gdb: remember previously selected thread per inferior

[Kevin Buettner <kevinb@redhat.com>]

Hi Klaus,

This is much better!  Just a few nits to fix...

On Fri, 11 Sep 2026 08:10:15 +0000
Klaus Gerlicher <klaus.gerlicher@intel.com> wrote:

[...]
> @@ -1255,5 +1310,22 @@ Show printing of inferior events (such as inferior start and exit)."), NULL,
>  	 show_print_inferior_events,
>  	 &setprintlist, &showprintlist);
>  
> +  add_setshow_boolean_cmd ("remember-threads-per-inferior", no_class,
> +	 &remember_inferior_threads, _("\
> +Set whether GDB will cache the current thread in each inferior."), _("\
> +Show whether GDB will cache the current thread in each inferior."), _("\
> +When on, GDB records which thread was current when switching away from\n\
> +an inferior, and automatically restores that thread when switching back\n\
> +to that inferior (if the thread still exists).  When off, GDB selects\n\
> +the first available thread."),
> +	 set_remember_inferior_threads,
> +	 NULL,
> +	 &setlist, &showlist);

Please change the set/show help strings to use "remember" instead of
"cache".

> +
>    create_internalvar_type_lazy ("_inferior", &inferior_funcs, NULL);
> +
> +  /* Observe user_selected_context_changed to store the current user
> +     thread.  */
> +  gdb::observers::user_selected_context_changed.attach (
> +      inferiors_on_user_selected_context_changed, "inferiors");
>  }
> diff --git a/gdb/inferior.h b/gdb/inferior.h
> index accd36740c3..b2bfa1a4029 100644
> --- a/gdb/inferior.h
> +++ b/gdb/inferior.h
> @@ -276,6 +276,10 @@ extern int stopped_by_random_signal;
>     `set print inferior-events'.  */
>  extern bool print_inferior_events;
>  
> +/* Control whether GDB remembers the selected thread per inferior, set with
> +   `set remember-threads-per-inferior'.  */
> +extern bool remember_inferior_threads;
> +
>  /* Anything but NO_STOP_QUIETLY means we expect a trap and the caller
>     will handle it themselves.  STOP_QUIETLY is used when running in
>     the shell before the child program has been exec'd and when running
> @@ -696,6 +700,10 @@ class inferior : public refcounted_object,
>    /* Per inferior data-pointers required by other GDB modules.  */
>    registry<inferior> registry_fields;
>  
> +  /* The last thread that was current when inferior was switched away
> +     from.  */
> +  thread_info_ref last_user_thread;
> +
>  private:
>  
>    /* Unpush TARGET and assert that it worked.  */
> @@ -902,6 +910,12 @@ extern void print_selected_inferior (struct ui_out *uiout);
>  extern void switch_to_inferior_and_push_target
>    (inferior *new_inf, bool no_connection, inferior *org_inf);
>  
> +/* Record the current inferior's selected thread, so it can be
> +   restored later.  GDB will select the recorded thread, if alive,
> +   instead of any thread from the current inferior.  */
> +
> +extern void save_inferior_last_thread ();
> +
>  /* Return true if ID is a valid global inferior number.  */
>  
>  inline bool
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index b9618fb6422..caff2e97aee 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -4886,7 +4886,17 @@ fetch_inferior_event ()
>  	    if (!non_stop
>  		&& cmd_done
>  		&& ecs.ws.kind () != TARGET_WAITKIND_NO_RESUMED)
> -	      restore_thread.dont_restore ();
> +	      {
> +		restore_thread.dont_restore ();
> +
> +		/* Save current thread for remember-threads-per-inferior feature.
> +		   This handles automatic event-driven thread switches (breakpoints,
> +		   signals, schedule-multiple execution) which don't trigger the
> +		   user_selected_context_changed observer.  The observer only fires
> +		   for explicit user commands like "thread X" or "inferior Y".  */
> +		if (remember_inferior_threads)
> +		  save_inferior_last_thread ();
> +	      }
>  	  }
>        }
>  
> diff --git a/gdb/testsuite/gdb.base/inferior-switch.c b/gdb/testsuite/gdb.base/inferior-switch.c
> new file mode 100644
> index 00000000000..107090d003c
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/inferior-switch.c
> @@ -0,0 +1,42 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +   Copyright 2024 Free Software Foundation, Inc.

Update copyright dates to 2024-2026.

[...]
> diff --git a/gdb/testsuite/gdb.base/inferior-switch.exp b/gdb/testsuite/gdb.base/inferior-switch.exp
> new file mode 100644
> index 00000000000..b118059638d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/inferior-switch.exp
> @@ -0,0 +1,187 @@
> +# Copyright 2024 Free Software Foundation, Inc.

Likewise.

With those nits fixed:

Approved-By: Kevin Buettner <kevinb@redhat.com>