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--                                                                          --

--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --

--                                                                          --

--                  S Y S T E M . O S _ P R I M I T I V E S                 --

--                                                                          --

--                                  S p e c                                 --

--                                                                          --

--          Copyright (C) 1998-2009, Free Software Foundation, Inc.         --

--                                                                          --

-- GNARL is free software; you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNARL was developed by the GNARL team at Florida State University.       --

-- Extensive contributions were provided by Ada Core Technologies, Inc.     --

--                                                                          --

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--  This package provides low level primitives used to implement clock and

--  delays in non tasking applications on Alpha/VMS.

--  The choice of the real clock/delay implementation (depending on whether

--  tasking is involved or not) is done via soft links (see s-soflin.ads)

--  NEVER add any dependency to tasking packages here

package System.OS_Primitives is

   pragma Preelaborate;

   subtype OS_Time is Long_Integer;

   --  System time on VMS is used for performance reasons.

   --  Note that OS_Time is *not* the same as Ada.Calendar.Time, the

   --  difference being that relative OS_Time is negative, but relative

   --  Calendar.Time is positive.

   --  See Ada.Calendar.Delays for more information on VMS Time.

   Max_Sensible_Delay : constant Duration :=

                          Duration'Min (183 * 24 * 60 * 60.0,

                                        Duration'Last);

   --  Max of half a year delay, needed to prevent exceptions for large delay

   --  values. It seems unlikely that any test will notice this restriction,

   --  except in the case of applications setting the clock at run time (see

   --  s-tastim.adb). Also note that a larger value might cause problems (e.g

   --  overflow, or more likely OS limitation in the primitives used). In the

   --  case where half a year is too long (which occurs in high integrity mode

   --  with 32-bit words, and possibly on some specific ports of GNAT),

   --  Duration'Last is used instead.

   procedure Initialize;

   --  Initialize global settings related to this package. This procedure

   --  should be called before any other subprograms in this package. Note

   --  that this procedure can be called several times.

   function OS_Clock return OS_Time;

   --  Returns "absolute" time, represented as an offset

   --  relative to "the Epoch", which is Nov 17, 1858 on VMS.

   function Clock return Duration;

   pragma Inline (Clock);

   --  Returns "absolute" time, represented as an offset relative to "the

   --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This

   --  implementation is affected by system's clock changes.

   function Monotonic_Clock return Duration;

   pragma Inline (Monotonic_Clock);

   --  Returns "absolute" time, represented as an offset relative to "the Unix

   --  Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is

   --  immune to the system's clock changes.

   Relative          : constant := 0;

   Absolute_Calendar : constant := 1;

   Absolute_RT       : constant := 2;

   --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies

   --  on these values. So any change here must be reflected in corresponding

   --  changes in the compiler.

   procedure Timed_Delay (Time : Duration; Mode : Integer);

   --  Implements the semantics of the delay statement when no tasking is used

   --  in the application.

   --

   --    Mode is one of the three values above

   --

   --    Time is a relative or absolute duration value, depending on Mode.

   --

   --  Note that currently Ada.Real_Time always uses the tasking run time,

   --  so this procedure should never be called with Mode set to Absolute_RT.

   --  This may change in future or bare board implementations.

   function To_Duration (T : OS_Time; Mode : Integer) return Duration;

   --  Convert VMS system time to Duration

   --  Mode is one of the three values above

   function To_OS_Time (D : Duration; Mode : Integer) return OS_Time;

   --  Convert Duration to VMS system time

   --  Mode is one of the three values above

end System.OS_Primitives;