--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/ada/libgnarl/a-dispat.adb	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,57 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT RUN-TIME COMPONENTS                         --
+--                                                                          --
+--                       A D A . D I S P A T C H I N G                      --
+--                                                                          --
+--                                 B o d y                                  --
+--                                                                          --
+--             Copyright (C) 2015-2017, Free Software Foundation, Inc.      --
+--                                                                          --
+-- GNAT is free software;  you can  redistribute it  and/or modify it under --
+-- terms of the  GNU General Public License as published  by the Free Soft- --
+-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
+-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
+--                                                                          --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception,   --
+-- version 3.1, as published by the Free Software Foundation.               --
+--                                                                          --
+-- You should have received a copy of the GNU General Public License and    --
+-- a copy of the GCC Runtime Library Exception along with this program;     --
+-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
+-- <http://www.gnu.org/licenses/>.                                          --
+--                                                                          --
+-- GNAT was originally developed  by the GNAT team at  New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc.      --
+--                                                                          --
+------------------------------------------------------------------------------
+
+with Ada.Exceptions;
+with System.Tasking;
+with System.Task_Primitives.Operations;
+
+package body Ada.Dispatching is
+
+   procedure Yield is
+      Self_Id : constant System.Tasking.Task_Id :=
+                  System.Task_Primitives.Operations.Self;
+
+   begin
+      --  If pragma Detect_Blocking is active, Program_Error must be
+      --  raised if this potentially blocking operation is called from a
+      --  protected action.
+
+      if System.Tasking.Detect_Blocking
+        and then Self_Id.Common.Protected_Action_Nesting > 0
+      then
+         Ada.Exceptions.Raise_Exception
+           (Program_Error'Identity, "potentially blocking operation");
+      else
+         System.Task_Primitives.Operations.Yield;
+      end if;
+   end Yield;
+
+end Ada.Dispatching;