Re: [PATCHv2] gdb: new $_inferior_thread_count convenience variable

[Luis Machado <luis.machado@arm.com>]

On 11/3/22 14:42, Andrew Burgess via Gdb-patches wrote:
> Simon, Luis,  thanks for your feedback.
> 
> Changes since v1:
> 
>    1. Rename variable to $_inferior_thread_count.
> 
>    2. Use "live" in the docs and NEWS file to describe the threads
>    being counted.  I do still use "non-exited" within the commit
>    message and comments, as this is how "live" is actually implemented
>    within GDB.
> 
>    3. Updated the docs to mention that in non-stop mode the value of
>    $_inferior_thread_count will not be stable.
> 
> Thanks,
> Andrew
> 
> ---
> 
> Add a new convenience variable $_inferior_thread_count that contains
> the number of live (non-exited) threads in the current inferior.  This
> can be used in command scripts, or breakpoint conditions, etc to
> adjust the behaviour for multi-threaded inferiors.
> 
> This value is only stable in all-stop mode.  In non-stop mode, where
> new threads can be started, and existing threads exit, at any time,
> this convenience variable can give a different value each time it is
> evaluated.
> ---
>   gdb/NEWS                           |  3 +++
>   gdb/doc/gdb.texinfo                | 14 ++++++++++++--
>   gdb/testsuite/gdb.base/default.exp |  1 +
>   gdb/testsuite/gdb.multi/tids.exp   | 20 ++++++++++++++++++++
>   gdb/thread.c                       | 26 ++++++++++++++++++++++++++
>   gdbsupport/iterator-range.h        |  4 ++++
>   6 files changed, 66 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 8b519a648f7..8857dedb8b8 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -71,6 +71,9 @@
>     For both /r and /b GDB is now better at using whitespace in order to
>     align the disassembled instruction text.
>   
> +* New convenience variable $_inferior_thread_count contains the number
> +  of live threads in the current inferior.
> +
>   * New commands
>   
>   maintenance set ignore-prologue-end-flag on|off
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index ea66f4ee42d..82f7fd66bf0 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -3642,8 +3642,15 @@
>   @samp{$_gthread} contain, respectively, the per-inferior thread number
>   and the global thread number of the current thread.  You may find this
>   useful in writing breakpoint conditional expressions, command scripts,
> -and so forth.  @xref{Convenience Vars,, Convenience Variables}, for
> -general information on convenience variables.
> +and so forth.  The convenience variable @samp{$_inferior_thread_count}
> +contains the number of live threads in the current inferior.
> +@xref{Convenience Vars,, Convenience Variables}, for general
> +information on convenience variables.
> +
> +When running in non-stop mode (@pxref{Non-Stop Mode}), where new
> +threads can be created, and existing threads exit, at any time,
> +@samp{$_inferior_thread_count} could return a different value each
> +time it is evaluated.
>   
>   If @value{GDBN} detects the program is multi-threaded, it augments the
>   usual message about stopping at a breakpoint with the ID and name of
> @@ -12655,6 +12662,9 @@
>   @item $_gthread
>   The global number of the current thread.  @xref{global thread numbers}.
>   
> +@item $_inferior_thread_count
> +The number of live threads in the current inferior.  @xref{Threads}.
> +
>   @item $_gdb_major
>   @itemx $_gdb_minor
>   @vindex $_gdb_major@r{, convenience variable}
> diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
> index 29e76642830..f3e4b2867ef 100644
> --- a/gdb/testsuite/gdb.base/default.exp
> +++ b/gdb/testsuite/gdb.base/default.exp
> @@ -584,6 +584,7 @@ set show_conv_list \
>   	{$_thread = 0} \
>   	{$_gthread = 0} \
>   	{$_inferior = 1} \
> +	{$_inferior_thread_count = 0} \
>   	{$_exception = <error: No frame selected>} \
>   	{$_probe_argc = <error: No frame selected>} \
>   	{$_probe_arg0 = <error: No frame selected>} \
> diff --git a/gdb/testsuite/gdb.multi/tids.exp b/gdb/testsuite/gdb.multi/tids.exp
> index fb7c2a29a71..23668caf18f 100644
> --- a/gdb/testsuite/gdb.multi/tids.exp
> +++ b/gdb/testsuite/gdb.multi/tids.exp
> @@ -123,6 +123,8 @@ with_test_prefix "single inferior" {
>       info_threads "" "1"
>   
>       gdb_test "thread" "Current thread is 1 .*"
> +
> +    gdb_test "print \$_inferior_thread_count" " = 1"
>   }
>   
>   # "info threads" while there are multiple inferiors should show
> @@ -140,8 +142,14 @@ with_test_prefix "two inferiors" {
>       gdb_test "inferior 2" "Switching to inferior 2 .*" "switch to inferior 2"
>       gdb_test "file ${binfile}" ".*" "load file in inferior 2"
>   
> +    gdb_test "print \$_inferior_thread_count" " = 0" \
> +	"no threads before we start the second inferior"
> +
>       runto_main
>   
> +    gdb_test "print \$_inferior_thread_count" " = 1" \
> +	"no other threads started yet"
> +
>       # Now that we've added another inferior, thread IDs now show the
>       # inferior number.
>       info_threads "" "1.1 2.1" \
> @@ -153,8 +161,14 @@ with_test_prefix "two inferiors" {
>       gdb_breakpoint "thread_function1"
>   
>       gdb_continue_to_breakpoint "once"
> +    gdb_test "print \$_inferior_thread_count" " = 2" \
> +	"second thread started in inferior 2"
>       gdb_test "inferior 1" "Switching to inferior 1 .*"
> +    gdb_test "print \$_inferior_thread_count" " = 1" \
> +	"still only one thread in inferior 1"
>       gdb_continue_to_breakpoint "twice"
> +    gdb_test "print \$_inferior_thread_count" " = 2" \
> +	"second thread started in inferior 1"
>   
>       info_threads "" "1.1 1.2 2.1 2.2" \
>   	"info threads again"
> @@ -187,9 +201,15 @@ with_test_prefix "two inferiors" {
>   
>   	gdb_test "inferior 2" "Switching to inferior 2 .*"
>   	gdb_continue_to_breakpoint "once"
> +	gdb_test "print \$_inferior_thread_count" " = 3" \
> +	    "third thread started in inferior 2"
>   
>   	gdb_test "inferior 1" "Switching to inferior 1 .*"
> +	gdb_test "print \$_inferior_thread_count" " = 2" \
> +	    "still only two threads in inferior 1"
>   	gdb_continue_to_breakpoint "twice"
> +	gdb_test "print \$_inferior_thread_count" " = 3" \
> +	    "third thread started in inferior 1"
>       }
>   
>       thr_apply_info_thr "1" \
> diff --git a/gdb/thread.c b/gdb/thread.c
> index 349fc01dd48..d176d1d9895 100644
> --- a/gdb/thread.c
> +++ b/gdb/thread.c
> @@ -2123,6 +2123,22 @@ global_thread_id_make_value (struct gdbarch *gdbarch, struct internalvar *var,
>     return thread_num_make_value_helper (gdbarch, 1);
>   }
>   
> +/* Return a new value for the number of non-exited threads in the current
> +   inferior.  If there are no threads in the current inferior return a
> +   value of 0.  */
> +
> +static struct value *
> +inferior_thread_count_make_value (struct gdbarch *gdbarch,
> +				  struct internalvar *var, void *ignore)
> +{
> +  int int_val = 0;
> +
> +  if (inferior_ptid != null_ptid)
> +    int_val = current_inferior ()->non_exited_threads ().size ();
> +
> +  return value_from_longest (builtin_type (gdbarch)->builtin_int, int_val);
> +}
> +
>   /* Commands with a prefix of `thread'.  */
>   struct cmd_list_element *thread_cmd_list = NULL;
>   
> @@ -2142,6 +2158,14 @@ static const struct internalvar_funcs gthread_funcs =
>     NULL,
>   };
>   
> +/* Implementation of `_inferior_thread_count` convenience variable.  */
> +
> +static const struct internalvar_funcs inferior_thread_count_funcs =
> +{
> +  inferior_thread_count_make_value,
> +  NULL,
> +};
> +
>   void _initialize_thread ();
>   void
>   _initialize_thread ()
> @@ -2258,4 +2282,6 @@ When on messages about thread creation and deletion are printed."),
>   
>     create_internalvar_type_lazy ("_thread", &thread_funcs, NULL);
>     create_internalvar_type_lazy ("_gthread", &gthread_funcs, NULL);
> +  create_internalvar_type_lazy ("_inferior_thread_count",
> +				&inferior_thread_count_funcs, NULL);
>   }
> diff --git a/gdbsupport/iterator-range.h b/gdbsupport/iterator-range.h
> index d35b03a3392..c99bdc8de07 100644
> --- a/gdbsupport/iterator-range.h
> +++ b/gdbsupport/iterator-range.h
> @@ -53,6 +53,10 @@ struct iterator_range
>     IteratorType end () const
>     { return m_end; }
>   
> +  /* The number of items in this iterator_range.  */
> +  std::size_t size () const
> +  { return std::distance (m_begin, m_end); }
> +
>   private:
>     IteratorType m_begin, m_end;
>   };

LGTM.