gcc/ada/s-taasde.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
   4 --                                                                          --
   5 --           S Y S T E M . T A S K I N G . A S Y N C _ D E L A Y S          --
   6 --                                                                          --
   7 --                                  S p e c                                 --
   8 --                                                                          --
   9 --                                                                          --
  10 --          Copyright (C) 1998-2001 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNARL was developed by the GNARL team at Florida State University. It is --
  31 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  32 -- State University (http://www.gnat.com).                                  --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 --  This package contains the procedures to implements timeouts (delays)
  37 --  for asynchronous select statements.
  38
  39 --  Note: the compiler generates direct calls to this interface, via Rtsfind.
  40 --  Any changes to this interface may require corresponding compiler changes.
  41
  42 package System.Tasking.Async_Delays is
  43
  44    --  Suppose the following source code is given:
  45
  46    --  select delay When;
  47    --     ...continuation for timeout case...
  48    --  then abort
  49    --     ...abortable part...
  50    --  end select;
  51
  52    --  The compiler should expand this to the following:
  53
  54    --  declare
  55    --     DB : aliased Delay_Block;
  56    --  begin
  57    --     if System.Tasking.Async_Delays.Enqueue_Duration
  58    --       (When, DB'Unchecked_Access)
  59    --     then
  60    --        begin
  61    --           A101b : declare
  62    --              procedure _clean is
  63    --              begin
  64    --                 System.Tasking.Async_Delays.Cancel_Async_Delay
  65    --                   (DB'Unchecked_Access);
  66    --                 return;
  67    --              end _clean;
  68    --           begin
  69    --              abort_undefer.all;
  70    --              ...abortable part...
  71    --           exception
  72    --              when all others =>
  73    --                 declare
  74    --                    E105b : exception_occurrence;
  75    --                 begin
  76    --                    save_occurrence (E105b, get_current_excep.all.all);
  77    --                    _clean;
  78    --                    reraise_occurrence_no_defer (E105b);
  79    --                 end;
  80    --           at end
  81    --              _clean;
  82    --           end A101b;
  83    --        exception
  84    --           when _abort_signal =>
  85    --              abort_undefer.all;
  86    --        end;
  87    --     end if;
  88    --
  89    --     if Timed_Out (DB'Unchecked_Access) then
  90    --        ...continuation for timeout case...
  91    --     end if;
  92    --  end;
  93
  94    -----------------
  95    -- Delay_Block --
  96    -----------------
  97
  98    type Delay_Block is limited private;
  99    type Delay_Block_Access is access all Delay_Block;
 100
 101    function Enqueue_Duration
 102      (T : in Duration;
 103       D : Delay_Block_Access) return Boolean;
 104    --  Enqueue the specified relative delay. Returns True if the delay has
 105    --  been enqueued, False if it has already expired.
 106    --  If the delay has been enqueued, abortion is deferred.
 107
 108    procedure Cancel_Async_Delay (D : Delay_Block_Access);
 109    --  Cancel the specified asynchronous delay
 110
 111    function Timed_Out (D : Delay_Block_Access) return Boolean;
 112    pragma Inline (Timed_Out);
 113    --  Return True if the delay specified in D has timed out
 114
 115    --  There are child units for delays on Ada.Calendar.Time and
 116    --  Ada.Real_Time.Time, so that an application will not need to link in
 117    --  features that is not using.
 118
 119 private
 120
 121    type Delay_Block is record
 122       Self_Id     : Task_ID;
 123       --  ID of the calling task
 124
 125       Level       : ATC_Level_Base;
 126       --  Normally Level is the ATC nesting level of the
 127       --  async. select statement to which this delay belongs, but
 128       --  after a call has been dequeued we set it to
 129       --  ATC_Level_Infinity so that the Cancel operation can
 130       --  detect repeated calls, and act idempotently.
 131
 132       Resume_Time : Duration;
 133       --  The absolute wake up time, represented as Duration
 134
 135       Timed_Out   : Boolean := False;
 136       --  Set to true if the delay has timed out
 137
 138       Succ, Pred  : Delay_Block_Access;
 139       --  A double linked list
 140    end record;
 141
 142    --  The above "overlaying" of Self_ID and Level to hold other
 143    --  data that has a non-overlapping lifetime is an unabashed
 144    --  hack to save memory.
 145
 146    procedure Time_Enqueue
 147      (T : Duration;
 148       D : Delay_Block_Access);
 149    pragma Inline (Time_Enqueue);
 150    --  Used by the child units to enqueue delays on the timer queue
 151    --  implemented in the body of this package.
 152
 153 end System.Tasking.Async_Delays;