gcc/ada/libgnat/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) 1998-2020, 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 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT 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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNARL was developed by the GNARL team at Florida State University.       --
  28 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package provides low level primitives used to implement clock and
  33 --  delays in non tasking applications.
  34
  35 --  The choice of the real clock/delay implementation (depending on whether
  36 --  tasking is involved or not) is done via soft links (see s-soflin.ads)
  37
  38 --  NEVER add any dependency to tasking packages here
  39
  40 package System.OS_Primitives is
  41    pragma Preelaborate;
  42
  43    Max_Sensible_Delay : constant Duration :=
  44                           Duration'Min (183 * 24 * 60 * 60.0,
  45                                         Duration'Last);
  46    --  Max of half a year delay, needed to prevent exceptions for large delay
  47    --  values. It seems unlikely that any test will notice this restriction,
  48    --  except in the case of applications setting the clock at run time (see
  49    --  s-tastim.adb). Also note that a larger value might cause problems (e.g
  50    --  overflow, or more likely OS limitation in the primitives used). In the
  51    --  case where half a year is too long (which occurs in high integrity mode
  52    --  with 32-bit words, and possibly on some specific ports of GNAT),
  53    --  Duration'Last is used instead.
  54
  55    Max_System_Delay : constant Duration := Max_Sensible_Delay;
  56    --  If the Max_System_Delay is larger it doesn't matter. Setting it equal
  57    --  allows optimization of code in some targets delay functions.
  58
  59    procedure Initialize;
  60    --  Initialize global settings related to this package. This procedure
  61    --  should be called before any other subprograms in this package. Note
  62    --  that this procedure can be called several times.
  63
  64    function Clock return Duration;
  65    pragma Inline (Clock);
  66    --  Returns "absolute" time, represented as an offset relative to "the
  67    --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
  68    --  implementation is affected by system's clock changes.
  69
  70    Relative          : constant := 0;
  71    Absolute_Calendar : constant := 1;
  72    Absolute_RT       : constant := 2;
  73    --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
  74    --  on these values. So any change here must be reflected in corresponding
  75    --  changes in the compiler.
  76
  77    procedure Timed_Delay (Time : Duration; Mode : Integer);
  78    --  Implements the semantics of the delay statement when no tasking is used
  79    --  in the application.
  80    --
  81    --    Mode is one of the three values above
  82    --
  83    --    Time is a relative or absolute duration value, depending on Mode.
  84    --
  85    --  Note that currently Ada.Real_Time always uses the tasking run time,
  86    --  so this procedure should never be called with Mode set to Absolute_RT.
  87    --  This may change in future or bare board implementations.
  88
  89 end System.OS_Primitives;