gcc/ada/s-osprim-vms.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 on Alpha/VMS.
  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    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 :=
  53                           Duration'Min (183 * 24 * 60 * 60.0,
  54                                         Duration'Last);
  55    --  Max of half a year delay, needed to prevent exceptions for large delay
  56    --  values. It seems unlikely that any test will notice this restriction,
  57    --  except in the case of applications setting the clock at run time (see
  58    --  s-tastim.adb). Also note that a larger value might cause problems (e.g
  59    --  overflow, or more likely OS limitation in the primitives used). In the
  60    --  case where half a year is too long (which occurs in high integrity mode
  61    --  with 32-bit words, and possibly on some specific ports of GNAT),
  62    --  Duration'Last is used instead.
  63
  64    procedure Initialize;
  65    --  Initialize global settings related to this package. This procedure
  66    --  should be called before any other subprograms in this package. Note
  67    --  that this procedure can be called several times.
  68
  69    function OS_Clock return OS_Time;
  70    --  Returns "absolute" time, represented as an offset
  71    --  relative to "the Epoch", which is Nov 17, 1858 on VMS.
  72
  73    function Clock return Duration;
  74    pragma Inline (Clock);
  75    --  Returns "absolute" time, represented as an offset relative to "the
  76    --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
  77    --  implementation is affected by system's clock changes.
  78
  79    function Monotonic_Clock return Duration;
  80    pragma Inline (Monotonic_Clock);
  81    --  Returns "absolute" time, represented as an offset relative to "the Unix
  82    --  Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is
  83    --  immune to the system's clock changes.
  84
  85    Relative          : constant := 0;
  86    Absolute_Calendar : constant := 1;
  87    Absolute_RT       : constant := 2;
  88    --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
  89    --  on these values. So any change here must be reflected in corresponding
  90    --  changes in the compiler.
  91
  92    procedure Timed_Delay (Time : Duration; Mode : Integer);
  93    --  Implements the semantics of the delay statement when no tasking is used
  94    --  in the application.
  95    --
  96    --    Mode is one of the three values above
  97    --
  98    --    Time is a relative or absolute duration value, depending on Mode.
  99    --
 100    --  Note that currently Ada.Real_Time always uses the tasking run time,
 101    --  so this procedure should never be called with Mode set to Absolute_RT.
 102    --  This may change in future or bare board implementations.
 103
 104    function To_Duration (T : OS_Time; Mode : Integer) return Duration;
 105    --  Convert VMS system time to Duration
 106    --  Mode is one of the three values above
 107
 108    function To_OS_Time (D : Duration; Mode : Integer) return OS_Time;
 109    --  Convert Duration to VMS system time
 110    --  Mode is one of the three values above
 111
 112 end System.OS_Primitives;