gcc/ada/s-taasde.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNAT 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 --          Copyright (C) 1998-2006, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNARL was developed by the GNARL team at Florida State University.       --
  30 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This package contains the procedures to implements timeouts (delays) for
  35 --  asynchronous select statements.
  36
  37 --  Note: the compiler generates direct calls to this interface, via Rtsfind.
  38 --  Any changes to this interface may require corresponding compiler changes.
  39
  40 package System.Tasking.Async_Delays is
  41
  42    --  Suppose the following source code is given:
  43
  44    --  select delay When;
  45    --     ...continuation for timeout case...
  46    --  then abort
  47    --     ...abortable part...
  48    --  end select;
  49
  50    --  The compiler should expand this to the following:
  51
  52    --  declare
  53    --     DB : aliased Delay_Block;
  54    --  begin
  55    --     if System.Tasking.Async_Delays.Enqueue_Duration
  56    --       (When, DB'Unchecked_Access)
  57    --     then
  58    --        begin
  59    --           A101b : declare
  60    --              procedure _clean is
  61    --              begin
  62    --                 System.Tasking.Async_Delays.Cancel_Async_Delay
  63    --                   (DB'Unchecked_Access);
  64    --                 return;
  65    --              end _clean;
  66    --           begin
  67    --              abort_undefer.all;
  68    --              ...abortable part...
  69    --           exception
  70    --              when all others =>
  71    --                 declare
  72    --                    E105b : exception_occurrence;
  73    --                 begin
  74    --                    save_occurrence (E105b, get_current_excep.all.all);
  75    --                    _clean;
  76    --                    reraise_occurrence_no_defer (E105b);
  77    --                 end;
  78    --           at end
  79    --              _clean;
  80    --           end A101b;
  81    --        exception
  82    --           when _abort_signal =>
  83    --              abort_undefer.all;
  84    --        end;
  85    --     end if;
  86    --
  87    --     if Timed_Out (DB'Unchecked_Access) then
  88    --        ...continuation for timeout case...
  89    --     end if;
  90    --  end;
  91
  92    -----------------
  93    -- Delay_Block --
  94    -----------------
  95
  96    type Delay_Block is limited private;
  97    type Delay_Block_Access is access all Delay_Block;
  98
  99    function Enqueue_Duration
 100      (T : Duration;
 101       D : Delay_Block_Access) return Boolean;
 102    --  Enqueue the specified relative delay. Returns True if the delay has
 103    --  been enqueued, False if it has already expired. If the delay has been
 104    --  enqueued, abort is deferred.
 105
 106    procedure Cancel_Async_Delay (D : Delay_Block_Access);
 107    --  Cancel the specified asynchronous delay
 108
 109    function Timed_Out (D : Delay_Block_Access) return Boolean;
 110    pragma Inline (Timed_Out);
 111    --  Return True if the delay specified in D has timed out
 112
 113    --  There are child units for delays on Ada.Calendar.Time and
 114    --  Ada.Real_Time.Time, so that an application will not need to link in
 115    --  features that is not using.
 116
 117 private
 118
 119    type Delay_Block is record
 120       Self_Id : Task_Id;
 121       --  ID of the calling task
 122
 123       Level : ATC_Level_Base;
 124       --  Normally Level is the ATC nesting level of the
 125       --  async. select statement to which this delay belongs, but
 126       --  after a call has been dequeued we set it to
 127       --  ATC_Level_Infinity so that the Cancel operation can
 128       --  detect repeated calls, and act idempotently.
 129
 130       Resume_Time : Duration;
 131       --  The absolute wake up time, represented as Duration
 132
 133       Timed_Out : Boolean := False;
 134       --  Set to true if the delay has timed out
 135
 136       Succ, Pred : Delay_Block_Access;
 137       --  A double linked list
 138    end record;
 139
 140    --  The above "overlaying" of Self_ID and Level to hold other
 141    --  data that has a non-overlapping lifetime is an unabashed
 142    --  hack to save memory.
 143
 144    procedure Time_Enqueue
 145      (T : Duration;
 146       D : Delay_Block_Access);
 147    pragma Inline (Time_Enqueue);
 148    --  Used by the child units to enqueue delays on the timer queue
 149    --  implemented in the body of this package.
 150
 151 end System.Tasking.Async_Delays;