* infrun.c (handle_inferior_event): Update comment around trying

to revert back to a stepping thread that has exited.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2009-06-10  Pedro Alves  <pedro@codesourcery.com>
+
+	* infrun.c (handle_inferior_event): Update comment around trying
+	to revert back to a stepping thread that has exited.
+
 2009-06-10  Cary Coutant  <ccoutant@google.com>
 
 	* dwarf2read.c (dwarf_decode_lines): Recognize and ignore

gdb/infrun.c

@@ -3496,9 +3496,25 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (!gdbarch_get_longjmp_target)\n");
 	      return;
 	    }
 
-	  /* If the stepping thread exited, then don't try reverting
-	     back to it, just keep going.  We need to query the target
-	     in case it doesn't support thread exit events.  */
+	  /* If the stepping thread exited, then don't try to switch
+	     back and resume it, which could fail in several different
+	     ways depending on the target.  Instead, just keep going.
+
+	     We can find a stepping dead thread in the thread list in
+	     two cases:
+
+	     - The target supports thread exit events, and when the
+	     target tries to delete the thread from the thread list,
+	     inferior_ptid pointed at the exiting thread.  In such
+	     case, calling delete_thread does not really remove the
+	     thread from the list; instead, the thread is left listed,
+	     with 'exited' state.
+
+	     - The target's debug interface does not support thread
+	     exit events, and so we have no idea whatsoever if the
+	     previously stepping thread is still alive.  For that
+	     reason, we need to synchronously query the target
+	     now.  */
 	  if (is_exited (tp->ptid)
 	      || !target_thread_alive (tp->ptid))
 	    {