Sort threads for thread apply all

downstream Fedora request:
	Please make it easier to find the backtrace of the crashing thread
	https://bugzilla.redhat.com/show_bug.cgi?id=1024504

Currently after loading a core file GDB prints:

Core was generated by `./threadcrash1'.
Program terminated with signal SIGSEGV, Segmentation fault.
8       *(volatile int *)0=0;
(gdb) _

there is nowhere seen which of the threads had crashed.  In reality GDB always
numbers that thread as #1 and it is the current thread that time.  But after
dumping all the info into a file for later analysis it is no longer obvious.
'thread apply all bt' even puts the thread #1 to the _end_ of the output!!!

I find maybe as good enough and with no risk of UI change flamewar to just
sort the threads by their number.  Currently they are printed as they happen
in the internal GDB list which has no advantage.  Printing thread #1 as the
first one with assumed 'thread apply all bt' (after the core file is loaded)
should make the complaint resolved I guess.

On Thu, 15 Jan 2015 20:29:07 +0100, Doug Evans wrote:
No objection to sorting the list, but if thread #1 is the important one,
then a concern could be it'll have scrolled off the screen (such a
concern has been voiced in another thread in another context),
and if not lost (say it's in an emacs buffer) one would still have
to scroll back to see it.
So one *could* still want #1 to be last.
Do we want an option to choose the sort direction?

gdb/ChangeLog
2015-01-22  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* NEWS (Changes since GDB 7.9): Add 'thread apply all' option
	'-ascending'.
	* thread.c (tp_array_compar_ascending, tp_array_compar): New.
	(thread_apply_all_command): Parse CMD for tp_array_compar_ascending.
	Sort tp_array using tp_array_compar.
	(_initialize_thread): Extend thread_apply_all_command help.

gdb/doc/ChangeLog
2015-01-22  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.texinfo (Threads): Describe -ascending for thread apply all.

1 files changed, 36 insertions, 1 deletions

diff --git a/gdb/thread.c b/gdb/thread.c
index 4bce212..a2a5a9b 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1381,6 +1381,24 @@ make_cleanup_restore_current_thread (void)
 			    restore_current_thread_cleanup_dtor);
 }
 
+/* If non-zero tp_array_compar should sort in ascending order, otherwise in
+   descending order.  */
+
+static int tp_array_compar_ascending;
+
+/* Sort an array for struct thread_info pointers by their NUM, order is
+   determined by TP_ARRAY_COMPAR_ASCENDING.  */
+
+static int
+tp_array_compar (const void *ap_voidp, const void *bp_voidp)
+{
+  const struct thread_info *const *ap = ap_voidp;
+  const struct thread_info *const *bp = bp_voidp;
+
+  return ((((*ap)->num > (*bp)->num) - ((*ap)->num < (*bp)->num))
+	  * (tp_array_compar_ascending ? +1 : -1));
+}
+
 /* Apply a GDB command to a list of threads.  List syntax is a whitespace
    seperated list of numbers, or ranges, or the keyword `all'.  Ranges consist
    of two numbers seperated by a hyphen.  Examples:
@@ -1397,6 +1415,14 @@ thread_apply_all_command (char *cmd, int from_tty)
   int tc;
   struct thread_array_cleanup ta_cleanup;
 
+  tp_array_compar_ascending = 0;
+  if (cmd != NULL
+      && check_for_argument (&cmd, "-ascending", strlen ("-ascending")))
+    {
+      cmd = skip_spaces (cmd);
+      tp_array_compar_ascending = 1;
+    }
+
   if (cmd == NULL || *cmd == '\000')
     error (_("Please specify a command following the thread ID list"));
 
@@ -1430,6 +1456,8 @@ thread_apply_all_command (char *cmd, int from_tty)
           i++;
         }
 
+      qsort (tp_array, i, sizeof (*tp_array), tp_array_compar);
+
       make_cleanup (set_thread_refcount, &ta_cleanup);
 
       for (k = 0; k != i; k++)
@@ -1738,7 +1766,14 @@ The new thread ID must be currently known."),
 		  &thread_apply_list, "thread apply ", 1, &thread_cmd_list);
 
   add_cmd ("all", class_run, thread_apply_all_command,
-	   _("Apply a command to all threads."), &thread_apply_list);
+	   _("\
+Apply a command to all threads.\n\
+\n\
+Usage: thread apply all [-ascending] <command>\n\
+-ascending: Call <command> for all threads in ascending order.\n\
+            The default is descending order.\
+"),
+	   &thread_apply_list);
 
   add_cmd ("name", class_run, thread_name_command,
 	   _("Set the current thread's name.\n\