gcc/ada/s-osprim.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA 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 --                             $Revision: 1.11 $
  10 --                                                                          --
  11 --          Copyright (C) 1998-2001 Free Software Foundation, Inc.          --
  12 --                                                                          --
  13 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
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  16 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
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  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
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  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNARL was developed by the GNARL team at Florida State University. It is --
  32 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  33 -- State University (http://www.gnat.com).                                  --
  34 --                                                                          --
  35 ------------------------------------------------------------------------------
  36
  37 --  This package provides low level primitives used to implement clock and
  38 --  delays in non tasking applications.
  39
  40 --  The choice of the real clock/delay implementation (depending on whether
  41 --  tasking is involved or not) is done via soft links (see s-tasoli.ads)
  42
  43 --  NEVER add any dependency to tasking packages here
  44
  45 package System.OS_Primitives is
  46
  47    Max_Sensible_Delay : constant Duration := 183 * 24 * 60 * 60.0;
  48    --  Max of half a year delay, needed to prevent exceptions for large
  49    --  delay values. It seems unlikely that any test will notice this
  50    --  restriction, except in the case of applications setting the clock at
  51    --  at run time (see s-tastim.adb). Also note that a larger value might
  52    --  cause problems (e.g overflow, or more likely OS limitation in the
  53    --  primitives used).
  54
  55    function Clock return Duration;
  56    pragma Inline (Clock);
  57    --  Returns "absolute" time, represented as an offset
  58    --  relative to "the Epoch", which is Jan 1, 1970 on unixes.
  59    --  This implementation is affected by system's clock changes.
  60
  61    function Monotonic_Clock return Duration;
  62    pragma Inline (Monotonic_Clock);
  63    --  Returns "absolute" time, represented as an offset
  64    --  relative to "the Epoch", which is Jan 1, 1970.
  65    --  This clock implementation is immune to the system's clock changes.
  66
  67    Relative          : constant := 0;
  68    Absolute_Calendar : constant := 1;
  69    Absolute_RT       : constant := 2;
  70    --  Values for Mode call below. Note that the compiler (exp_ch9.adb)
  71    --  relies on these values. So any change here must be reflected in
  72    --  corresponding changes in the compiler.
  73
  74    procedure Timed_Delay (Time : Duration; Mode : Integer);
  75    --  Implements the semantics of the delay statement when no tasking is
  76    --  used in the application.
  77    --
  78    --    Mode is one of the three values above
  79    --
  80    --    Time is a relative or absolute duration value, depending on Mode.
  81    --
  82    --  Note that currently Ada.Real_Time always uses the tasking run time, so
  83    --  this procedure should never be called with Mode set to Absolute_RT.
  84    --  This may change in future or bare board implementations.
  85
  86 end System.OS_Primitives;