New Language: Ada

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@45957 138bc75d-0d04-0410-961f-82ee72b054a4

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+------------------------------------------------------------------------------
+--                                                                          --
+--                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
+--                                                                          --
+--           S Y S T E M . T A S K I N G . A S Y N C _ D E L A Y S          --
+--                                                                          --
+--                                  S p e c                                 --
+--                                                                          --
+--                             $Revision: 1.1 $
+--                                                                          --
+--           Copyright (C) 1998-1999 Ada Core Technologies, Inc.            --
+--                                                                          --
+-- GNARL 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 2,  or (at your option) any later ver- --
+-- sion. GNARL 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.  See the GNU General Public License --
+-- for  more details.  You should have  received  a copy of the GNU General --
+-- Public License  distributed with GNARL; see file COPYING.  If not, write --
+-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
+-- MA 02111-1307, USA.                                                      --
+--                                                                          --
+-- As a special exception,  if other files  instantiate  generics from this --
+-- unit, or you link  this unit with other files  to produce an executable, --
+-- this  unit  does not  by itself cause  the resulting  executable  to  be --
+-- covered  by the  GNU  General  Public  License.  This exception does not --
+-- however invalidate  any other reasons why  the executable file  might be --
+-- covered by the  GNU Public License.                                      --
+--                                                                          --
+-- GNARL was developed by the GNARL team at Florida State University. It is --
+-- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
+-- State University (http://www.gnat.com).                                  --
+--                                                                          --
+------------------------------------------------------------------------------
+
+--  This package contains the procedures to implements timeouts (delays) on
+--  asynchronous select statements.
+
+--  Note: the compiler generates direct calls to this interface, via Rtsfind.
+--  Any changes to this interface may require corresponding compiler changes.
+
+package System.Tasking.Async_Delays is
+
+   --  Suppose the following source code is given:
+
+   --  select delay When;
+   --     ...continuation for timeout case...
+   --  then abort
+   --     ...abortable part...
+   --  end select;
+
+   --  The compiler should expand this to the following:
+
+   --  declare
+   --     DB : aliased Delay_Block;
+   --  begin
+   --     if System.Tasking.Async_Delays.Enqueue_Duration
+   --       (When, DB'Unchecked_Access)
+   --     then
+   --        begin
+   --           A101b : declare
+   --              procedure _clean is
+   --              begin
+   --                 System.Tasking.Async_Delays.Cancel_Async_Delay
+   --                   (DB'Unchecked_Access);
+   --                 return;
+   --              end _clean;
+   --           begin
+   --              abort_undefer.all;
+   --              ...abortable part...
+   --           exception
+   --              when all others =>
+   --                 declare
+   --                    E105b : exception_occurrence;
+   --                 begin
+   --                    save_occurrence (E105b, get_current_excep.all.all);
+   --                    _clean;
+   --                    reraise_occurrence_no_defer (E105b);
+   --                 end;
+   --           at end
+   --              _clean;
+   --           end A101b;
+   --        exception
+   --           when _abort_signal =>
+   --              abort_undefer.all;
+   --        end;
+   --     end if;
+   --
+   --     if Timed_Out (DB'Unchecked_Access) then
+   --        ...continuation for timeout case...
+   --     end if;
+   --  end;
+
+   -----------------
+   -- Delay_Block --
+   -----------------
+
+   type Delay_Block is limited private;
+   type Delay_Block_Access is access all Delay_Block;
+
+   function Enqueue_Duration
+     (T : in Duration;
+      D : Delay_Block_Access) return Boolean;
+   --  Enqueue the specified relative delay. Returns True if the delay has
+   --  been enqueued, False if it has already expired.
+   --  If the delay has been enqueued, abortion is deferred.
+
+   procedure Cancel_Async_Delay (D : Delay_Block_Access);
+   --  Cancel the specified asynchronous delay
+
+   function Timed_Out (D : Delay_Block_Access) return Boolean;
+   pragma Inline (Timed_Out);
+   --  Return True if the delay specified in D has timed out
+
+   --  There are child units for delays on Ada.Calendar.Time and
+   --  Ada.Real_Time.Time, so that an application will not need to link in
+   --  features that is not using.
+
+private
+
+   type Delay_Block is record
+      Self_Id     : Task_ID;
+      --  ID of the calling task
+
+      Level       : ATC_Level_Base;
+      --  Normally Level is the ATC nesting level of the
+      --  async. select statement to which this delay belongs, but
+      --  after a call has been dequeued we set it to
+      --  ATC_Level_Infinity so that the Cancel operation can
+      --  detect repeated calls, and act idempotently.
+
+      Resume_Time : Duration;
+      --  The absolute wake up time, represented as Duration
+
+      Timed_Out   : Boolean := False;
+      --  Set to true if the delay has timed out
+
+      Succ, Pred  : Delay_Block_Access;
+      --  A double linked list
+   end record;
+
+   --  The above "overlaying" of Self_ID and Level to hold other
+   --  data that has a non-overlapping lifetime is an unabashed
+   --  hack to save memory.
+
+   procedure Time_Enqueue
+     (T : Duration;
+      D : Delay_Block_Access);
+   pragma Inline (Time_Enqueue);
+   --  Used by the child units to enqueue delays on the timer queue
+   --  implemented in the body of this package.
+
+end System.Tasking.Async_Delays;