gdb: new $_inferior_threads convenience variable

  Add a new convenience variable $_inferior_threads that contains the
number of (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.
---
 gdb/NEWS                           |  3 +++
 gdb/doc/gdb.texinfo                |  9 +++++++--
 gdb/testsuite/gdb.base/default.exp |  1 +
 gdb/testsuite/gdb.multi/tids.exp   | 20 ++++++++++++++++++++
 gdb/thread.c                       | 25 +++++++++++++++++++++++++
 gdbsupport/iterator-range.h        |  4 ++++
 6 files changed, 60 insertions(+), 2 deletions(-)
  

On 11/2/22 10:34, Andrew Burgess via Gdb-patches wrote:
> Add a new convenience variable $_inferior_threads that contains the
> number of (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.

I don't really have time to look at the code, but here's a naming nit: I
think the name should contain "number" or "count" or something like
that.  The name "_inferior_threads" makes me think it yields a list of
threads, somehow.

Simon
  

On 11/2/22 14:34, Andrew Burgess via Gdb-patches wrote:
> Add a new convenience variable $_inferior_threads that contains the
> number of (non-exited) threads in the current inferior.  This can be

Just a couple comments.

Should we call them "live" threads instead of non-exited?

> used in command scripts, or breakpoint conditions, etc to adjust the
> behaviour for multi-threaded inferiors.

Could this number be a bit misleading at times? For example, a nonstop debugging session
with threads coming and going and everything running. I'm guessing the number wouldn't be reliable
enough to walk some list, right?

> ---
>   gdb/NEWS                           |  3 +++
>   gdb/doc/gdb.texinfo                |  9 +++++++--
>   gdb/testsuite/gdb.base/default.exp |  1 +
>   gdb/testsuite/gdb.multi/tids.exp   | 20 ++++++++++++++++++++
>   gdb/thread.c                       | 25 +++++++++++++++++++++++++
>   gdbsupport/iterator-range.h        |  4 ++++
>   6 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 8b519a648f7..3642d42e55a 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 $_inferior_threads contains the number of
> +  non-exited threads in the current inferior.
> +
>   * New commands
>   
>   maintenance set ignore-prologue-end-flag on|off
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index ea66f4ee42d..977cabd3771 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -3642,8 +3642,10 @@
>   @samp{$_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_threads}
> +contains the number of non-exited threads in the current inferior.
> +@xref{Convenience Vars,, Convenience Variables}, for general
> +information on convenience variables.
>   
>   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 +12657,9 @@
>   @item $_gthread
>   The global number of the current thread.  @xref{global thread numbers}.
>   
> +@item $_inferior_threads
> +The number of non-exited threads in the current inferior.  @xref{Threads}.
> +
>   @item $_gdb_major
>   @itemx $_gdb_minor
>   @vindex $_gdb_major@r{, convenience variable}
> diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
> index 29e76642830..cae131cc59b 100644
> --- a/gdb/testsuite/gdb.base/default.exp
> +++ b/gdb/testsuite/gdb.base/default.exp
> @@ -584,6 +584,7 @@ set show_conv_list \
>   	{$_thread = 0} \
>   	{$_gthread = 0} \
>   	{$_inferior = 1} \
> +	{$_inferior_threads = 0} \
>   	{$_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..1bcba02a1c9 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_threads" " = 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_threads" " = 0" \
> +	"no threads before we start the second inferior"
> +
>       runto_main
>   
> +    gdb_test "print \$_inferior_threads" " = 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_threads" " = 2" \
> +	"second thread started in inferior 2"
>       gdb_test "inferior 1" "Switching to inferior 1 .*"
> +    gdb_test "print \$_inferior_threads" " = 1" \
> +	"still only one thread in inferior 1"
>       gdb_continue_to_breakpoint "twice"
> +    gdb_test "print \$_inferior_threads" " = 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_threads" " = 3" \
> +	    "third thread started in inferior 2"
>   
>   	gdb_test "inferior 1" "Switching to inferior 1 .*"
> +	gdb_test "print \$_inferior_threads" " = 2" \
> +	    "still only two threads in inferior 1"
>   	gdb_continue_to_breakpoint "twice"
> +	gdb_test "print \$_inferior_threads" " = 3" \
> +	    "third thread started in inferior 1"
>       }
>   
>       thr_apply_info_thr "1" \
> diff --git a/gdb/thread.c b/gdb/thread.c
> index 349fc01dd48..f8942f1c5e4 100644
> --- a/gdb/thread.c
> +++ b/gdb/thread.c
> @@ -2123,6 +2123,21 @@ 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 threads in the current inferior.
> +   If there are no threads in the current inferior return a value of 0.  */
> +
> +static struct value *
> +inferior_threads_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 +2157,14 @@ static const struct internalvar_funcs gthread_funcs =
>     NULL,
>   };
>   
> +/* Implementation of `_inferior_threads` convenience variable.  */
> +
> +static const struct internalvar_funcs inferior_threads_funcs =
> +{
> +  inferior_threads_make_value,
> +  NULL,
> +};
> +
>   void _initialize_thread ();
>   void
>   _initialize_thread ()
> @@ -2258,4 +2281,6 @@ 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_threads",
> +				&inferior_threads_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;
>   };