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