[PATCH v4 23/44] gdb: allow switching to an inferior without threads

GPU inferiors may temporarily have no threads when no work is dispatched
to that GPU.  We still want to allow switching to such inferiors and
resuming them in all-stop mode (subsequent patch).

Also refactor the code a bit to split switching and notifying based on the
(potentially new) state.
---
 gdb/inferior.c | 36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/gdb/inferior.c b/gdb/inferior.c
index cc7d1cc4f94..b0112d4885c 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -767,29 +767,25 @@ inferior_command (const char *args, int from_tty)
       if (inf == NULL)
 	error (_("Inferior ID %d not known."), num);
 
-      if (inf->pid != 0)
+      if (inf->pid == 0)
+	switch_to_inferior_no_thread (inf);
+      else if (inf != current_inferior ())
 	{
-	  if (inf != current_inferior ())
-	    {
-	      thread_info *tp = any_thread_of_inferior (inf);
-	      if (tp == NULL)
-		error (_("Inferior has no threads."));
-
-	      switch_to_thread (tp);
-	    }
-
-	  notify_user_selected_context_changed
-	    (USER_SELECTED_INFERIOR
-	     | USER_SELECTED_THREAD
-	     | USER_SELECTED_FRAME);
+	  thread_info *tp = any_thread_of_inferior (inf);
+	  if (tp == nullptr)
+	    switch_to_inferior_no_thread (inf);
+	  else
+	    switch_to_thread (tp);
 	}
-      else
-	{
-	  switch_to_inferior_no_thread (inf);
 
-	  notify_user_selected_context_changed
-	    (USER_SELECTED_INFERIOR);
-	}
+      if (inferior_ptid == null_ptid)
+	notify_user_selected_context_changed
+	  (USER_SELECTED_INFERIOR);
+      else
+	notify_user_selected_context_changed
+	  (USER_SELECTED_INFERIOR
+	   | USER_SELECTED_THREAD
+	   | USER_SELECTED_FRAME);
 
       /* Switching current inferior may have made one of the inferiors
 	 prunable, so prune it.  */
-- 
2.43.0

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