[01/21] gdb: use intrusive_list for struct ui linked list

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4730d2904423..aaa7b2de14cd 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5454,9 +5454,9 @@  handle_no_resumed (struct execution_control_state *ecs)
     {
       bool any_sync = false;
 
-      for (ui *ui : all_uis ())
+      for (ui &ui : all_uis ())
 	{
-	  if (ui->prompt_state == PROMPT_BLOCKED)
+	  if (ui.prompt_state == PROMPT_BLOCKED)
 	    {
 	      any_sync = true;
 	      break;
diff --git a/gdb/top.c b/gdb/top.c
index 2322e55f1db4..483e201140e7 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1783,9 +1783,9 @@  quit_force (int *exit_arg, int from_tty)
 
 	  /* History is currently shared between all UIs.  If there's
 	     any UI with a terminal, save history.  */
-	  for (ui *ui : all_uis ())
+	  for (ui &ui : all_uis ())
 	    {
-	      if (ui->input_interactive_p ())
+	      if (ui.input_interactive_p ())
 		{
 		  save = 1;
 		  break;
diff --git a/gdb/ui.c b/gdb/ui.c
index 38ec61ea6731..f3dd14bfd3e0 100644
--- a/gdb/ui.c
+++ b/gdb/ui.c
@@ -33,7 +33,7 @@ 
 
 struct ui *main_ui;
 struct ui *current_ui;
-struct ui *ui_list;
+intrusive_list<ui> ui_list;
 
 /* The highest UI number ever assigned.  */
 
@@ -56,34 +56,13 @@  ui::ui (FILE *instream_, FILE *outstream_, FILE *errstream_)
 {
   unbuffer_stream (instream_);
 
-  if (ui_list == NULL)
-    ui_list = this;
-  else
-    {
-      struct ui *last;
-
-      for (last = ui_list; last->next != NULL; last = last->next)
-	;
-      last->next = this;
-    }
+  ui_list.push_back (*this);
 }
 
 ui::~ui ()
 {
-  struct ui *ui, *uiprev;
-
-  uiprev = NULL;
-
-  for (ui = ui_list; ui != NULL; uiprev = ui, ui = ui->next)
-    if (ui == this)
-      break;
-
-  gdb_assert (ui != NULL);
-
-  if (uiprev != NULL)
-    uiprev->next = next;
-  else
-    ui_list = next;
+  gdb_assert (this->is_linked ());
+  ui_list.erase (ui_list.iterator_to (*this));
 
   delete m_gdb_stdin;
   delete m_gdb_stdout;
diff --git a/gdb/ui.h b/gdb/ui.h
index ed75e041e5f2..c5e65c0393d8 100644
--- a/gdb/ui.h
+++ b/gdb/ui.h
@@ -51,7 +51,7 @@  enum prompt_state
    example, to create a separate MI channel on its own stdio
    streams.  */
 
-struct ui
+struct ui : public intrusive_list_node<ui>
 {
   /* Create a new UI.  */
   ui (FILE *instream, FILE *outstream, FILE *errstream);
@@ -59,9 +59,6 @@  struct ui
 
   DISABLE_COPY_AND_ASSIGN (ui);
 
-  /* Pointer to next in singly-linked list.  */
-  struct ui *next = nullptr;
-
   /* Convenient handle (UI number).  Unique across all UIs.  */
   int num;
 
@@ -172,16 +169,17 @@  extern struct ui *main_ui;
 extern struct ui *current_ui;
 
 /* The list of all UIs.  */
-extern struct ui *ui_list;
+extern intrusive_list<ui> ui_list;
 
 /* State for SWITCH_THRU_ALL_UIS.  */
 class switch_thru_all_uis
 {
 public:
 
-  switch_thru_all_uis () : m_iter (ui_list), m_save_ui (&current_ui)
+  switch_thru_all_uis () : m_iter (ui_list.begin ()), m_save_ui (&current_ui)
   {
-    current_ui = ui_list;
+    if (m_iter != ui_list.end ())
+      current_ui = &*m_iter;
   }
 
   DISABLE_COPY_AND_ASSIGN (switch_thru_all_uis);
@@ -189,22 +187,21 @@  class switch_thru_all_uis
   /* If done iterating, return true; otherwise return false.  */
   bool done () const
   {
-    return m_iter == NULL;
+    return m_iter == ui_list.end ();
   }
 
   /* Move to the next UI, setting current_ui if iteration is not yet
      complete.  */
   void next ()
   {
-    m_iter = m_iter->next;
-    if (m_iter != NULL)
-      current_ui = m_iter;
+    ++m_iter;
+    if (m_iter != ui_list.end ())
+      current_ui = &*m_iter;
   }
 
  private:
-
   /* Used to iterate through the UIs.  */
-  struct ui *m_iter;
+  intrusive_list<ui>::iterator m_iter;
 
   /* Save and restore current_ui.  */
   scoped_restore_tmpl<struct ui *> m_save_ui;
@@ -215,13 +212,11 @@  class switch_thru_all_uis
 #define SWITCH_THRU_ALL_UIS()		\
   for (switch_thru_all_uis stau_state; !stau_state.done (); stau_state.next ())
 
-using ui_range = next_range<ui>;
-
 /* An adapter that can be used to traverse over all UIs.  */
 static inline
-ui_range all_uis ()
+intrusive_list<ui> &all_uis ()
 {
-  return ui_range (ui_list);
+  return ui_list;
 }
 
 #endif /* UI_H */