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-- --
-- --
-- S Y S T E M . O S _ P R I M I T I V E S --
-- --
-- S p e c --
-- --
-- Copyright (C) 1998-2003 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 2, or (at your option) any later ver- --
-- sion. GNARL 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. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNARL; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNARL was developed by the GNARL team at Florida State University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- 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
-- NEVER add any dependency to tasking packages here
package System.OS_Primitives is
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,
-- 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
-- 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.
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 on unixes.
-- 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 Epoch", which is Jan 1, 1970.
-- 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;