File : s-osprim.ads


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

--  This package provides low level primitives used to implement clock and
--  delays in non tasking applications.

--  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;

   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 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.

end System.OS_Primitives;