gcc/ada/5vosprim.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 --                                                                          --
  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.       --
  31 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 --  This package provides low level primitives used to implement clock and
  36 --  delays in non tasking applications on Alpha/VMS
  37
  38 --  The choice of the real clock/delay implementation (depending on whether
  39 --  tasking is involved or not) is done via soft links (see s-tasoli.ads)
  40
  41 --  NEVER add any dependency to tasking packages here
  42
  43 package System.OS_Primitives is
  44
  45    subtype OS_Time is Long_Integer;
  46    --  System time on VMS is used for performance reasons.
  47    --  Note that OS_Time is *not* the same as Ada.Calendar.Time, the
  48    --  difference being that relative OS_Time is negative, but relative
  49    --  Calendar.Time is positive.
  50    --  See Ada.Calendar.Delays for more information on VMS Time.
  51
  52    Max_Sensible_Delay : constant Duration := 183 * 24 * 60 * 60.0;
  53    --  Max of half a year delay, needed to prevent exceptions for large
  54    --  delay values. It seems unlikely that any test will notice this
  55    --  restriction, except in the case of applications setting the clock at
  56    --  at run time (see s-tastim.adb). Also note that a larger value might
  57    --  cause problems (e.g overflow, or more likely OS limitation in the
  58    --  primitives used).
  59
  60    function OS_Clock return OS_Time;
  61    --  Returns "absolute" time, represented as an offset
  62    --  relative to "the Epoch", which is Nov 17, 1858 on VMS.
  63
  64    function Clock return Duration;
  65    pragma Inline (Clock);
  66    --  Returns "absolute" time, represented as an offset
  67    --  relative to "the Epoch", which is Jan 1, 1970 on unixes.
  68    --  This implementation is affected by system's clock changes.
  69
  70    function Monotonic_Clock return Duration;
  71    pragma Inline (Monotonic_Clock);
  72    --  Returns "absolute" time, represented as an offset
  73    --  relative to "the Epoch", which is Jan 1, 1970.
  74    --  This clock implementation is immune to the system's clock changes.
  75
  76    Relative          : constant := 0;
  77    Absolute_Calendar : constant := 1;
  78    Absolute_RT       : constant := 2;
  79    --  Values for Mode call below. Note that the compiler (exp_ch9.adb)
  80    --  relies on these values. So any change here must be reflected in
  81    --  corresponding changes in the compiler.
  82
  83    procedure Timed_Delay (Time : Duration; Mode : Integer);
  84    --  Implements the semantics of the delay statement when no tasking is
  85    --  used in the application.
  86    --
  87    --    Mode is one of the three values above
  88    --
  89    --    Time is a relative or absolute duration value, depending on Mode.
  90    --
  91    --  Note that currently Ada.Real_Time always uses the tasking run time, so
  92    --  this procedure should never be called with Mode set to Absolute_RT.
  93    --  This may change in future or bare board implementations.
  94
  95    function To_Duration (T : OS_Time; Mode : Integer) return Duration;
  96    --  Convert VMS system time to Duration
  97    --  Mode is one of the three values above
  98
  99    function To_OS_Time (D : Duration; Mode : Integer) return OS_Time;
 100    --  Convert Duration to VMS system time
 101    --  Mode is one of the three values above
 102
 103 end System.OS_Primitives;