gcc/ada/s-osprim.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
   4 --                                                                          --
   5 --                  S Y S T E M . O S _ P R I M I T I V E S                 --
   6 --                                                                          --
   7 --                                  S p e c                                 --
   8 --                                                                          --
   9 --          Copyright (C) 1998-2007, 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 provides low level primitives used to implement clock and
  35 --  delays in non tasking applications.
  36
  37 --  The choice of the real clock/delay implementation (depending on whether
  38 --  tasking is involved or not) is done via soft links (see s-soflin.ads)
  39
  40 --  NEVER add any dependency to tasking packages here
  41
  42 package System.OS_Primitives is
  43    pragma Preelaborate;
  44
  45    Max_Sensible_Delay : constant Duration :=
  46                           Duration'Min (183 * 24 * 60 * 60.0,
  47                                         Duration'Last);
  48    --  Max of half a year delay, needed to prevent exceptions for large delay
  49    --  values. It seems unlikely that any test will notice this restriction,
  50    --  except in the case of applications setting the clock at run time (see
  51    --  s-tastim.adb). Also note that a larger value might cause problems (e.g
  52    --  overflow, or more likely OS limitation in the primitives used). In the
  53    --  case where half a year is too long (which occurs in high integrity mode
  54    --  with 32-bit words, and possibly on some specific ports of GNAT),
  55    --  Duration'Last is used instead.
  56
  57    procedure Initialize;
  58    --  Initialize global settings related to this package. This procedure
  59    --  should be called before any other subprograms in this package. Note
  60    --  that this procedure can be called several times.
  61
  62    function Clock return Duration;
  63    pragma Inline (Clock);
  64    --  Returns "absolute" time, represented as an offset relative to "the
  65    --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
  66    --  implementation is affected by system's clock changes.
  67
  68    function Monotonic_Clock return Duration;
  69    pragma Inline (Monotonic_Clock);
  70    --  Returns "absolute" time, represented as an offset relative to "the Unix
  71    --  Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is
  72    --  immune to the system's clock changes.
  73
  74    Relative          : constant := 0;
  75    Absolute_Calendar : constant := 1;
  76    Absolute_RT       : constant := 2;
  77    --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
  78    --  on these values. So any change here must be reflected in corresponding
  79    --  changes in the compiler.
  80
  81    procedure Timed_Delay (Time : Duration; Mode : Integer);
  82    --  Implements the semantics of the delay statement when no tasking is used
  83    --  in the application.
  84    --
  85    --    Mode is one of the three values above
  86    --
  87    --    Time is a relative or absolute duration value, depending on Mode.
  88    --
  89    --  Note that currently Ada.Real_Time always uses the tasking run time,
  90    --  so this procedure should never be called with Mode set to Absolute_RT.
  91    --  This may change in future or bare board implementations.
  92
  93 end System.OS_Primitives;