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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                 --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--          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.     --

--                                                                          --

------------------------------------------------------------------------------

--  This is the NT version of this package

with System.Win32.Ext;

package body System.OS_Primitives is

   use System.Win32;

   use System.Win32.Ext;

   ----------------------------------------

   -- Data for the high resolution clock --

   ----------------------------------------

   --  Declare some pointers to access multi-word data above. This is needed

   --  to workaround a limitation in the GNU/Linker auto-import feature used

   --  to build the GNAT runtime DLLs. In fact the Clock and Monotonic_Clock

   --  routines are inlined and they are using some multi-word variables.

   --  GNU/Linker will fail to auto-import those variables when building

   --  libgnarl.dll. The indirection level introduced here has no measurable

   --  penalties.

   --  Note that access variables below must not be declared as constant

   --  otherwise the compiler optimization will remove this indirect access.

   type DA is access all Duration;

   --  Use to have indirect access to multi-word variables

   type LIA is access all LARGE_INTEGER;

   --  Use to have indirect access to multi-word variables

   type LLIA is access all Long_Long_Integer;

   --  Use to have indirect access to multi-word variables

   Tick_Frequency : aliased LARGE_INTEGER;

   TFA : constant LIA := Tick_Frequency'Access;

   --  Holds frequency of high-performance counter used by Clock

   --  Windows NT uses a 1_193_182 Hz counter on PCs.

   Base_Ticks : aliased LARGE_INTEGER;

   BTA : constant LIA := Base_Ticks'Access;

   --  Holds the Tick count for the base time

   Base_Monotonic_Ticks : aliased LARGE_INTEGER;

   BMTA : constant LIA := Base_Monotonic_Ticks'Access;

   --  Holds the Tick count for the base monotonic time

   Base_Clock : aliased Duration;

   BCA : constant DA := Base_Clock'Access;

   --  Holds the current clock for the standard clock's base time

   Base_Monotonic_Clock : aliased Duration;

   BMCA : constant DA := Base_Monotonic_Clock'Access;

   --  Holds the current clock for monotonic clock's base time

   Base_Time : aliased Long_Long_Integer;

   BTiA : constant LLIA := Base_Time'Access;

   --  Holds the base time used to check for system time change, used with

   --  the standard clock.

   procedure Get_Base_Time;

   --  Retrieve the base time and base ticks. These values will be used by

   --  clock to compute the current time by adding to it a fraction of the

   --  performance counter. This is for the implementation of a

   --  high-resolution clock. Note that this routine does not change the base

   --  monotonic values used by the monotonic clock.

   -----------

   -- Clock --

   -----------

   --  This implementation of clock provides high resolution timer values

   --  using QueryPerformanceCounter. This call return a 64 bits values (based

   --  on the 8253 16 bits counter). This counter is updated every 1/1_193_182

   --  times per seconds. The call to QueryPerformanceCounter takes 6

   --  microsecs to complete.

   function Clock return Duration is

      Max_Shift            : constant Duration        := 2.0;

      Hundreds_Nano_In_Sec : constant Long_Long_Float := 1.0E7;

      Current_Ticks        : aliased LARGE_INTEGER;

      Elap_Secs_Tick       : Duration;

      Elap_Secs_Sys        : Duration;

      Now                  : aliased Long_Long_Integer;

   begin

      if QueryPerformanceCounter (Current_Ticks'Access) = Win32.FALSE then

         return 0.0;

      end if;

      GetSystemTimeAsFileTime (Now'Access);

      Elap_Secs_Sys :=

        Duration (Long_Long_Float (abs (Now - BTiA.all)) /

                    Hundreds_Nano_In_Sec);

      Elap_Secs_Tick :=

        Duration (Long_Long_Float (Current_Ticks - BTA.all) /

                  Long_Long_Float (TFA.all));

      --  If we have a shift of more than Max_Shift seconds we resynchronize

      --  the Clock. This is probably due to a manual Clock adjustment, an

      --  DST adjustment or an NTP synchronisation. And we want to adjust the

      --  time for this system (non-monotonic) clock.

      if abs (Elap_Secs_Sys - Elap_Secs_Tick) > Max_Shift then

         Get_Base_Time;

         Elap_Secs_Tick :=

           Duration (Long_Long_Float (Current_Ticks - BTA.all) /

                     Long_Long_Float (TFA.all));

      end if;

      return BCA.all + Elap_Secs_Tick;

   end Clock;

   -------------------

   -- Get_Base_Time --

   -------------------

   procedure Get_Base_Time is

      --  The resolution for GetSystemTime is 1 millisecond

      --  The time to get both base times should take less than 1 millisecond.

      --  Therefore, the elapsed time reported by GetSystemTime between both

      --  actions should be null.

      epoch_1970     : constant := 16#19D_B1DE_D53E_8000#; -- win32 UTC epoch

      system_time_ns : constant := 100;                    -- 100 ns per tick

      Sec_Unit       : constant := 10#1#E9;

      Max_Elapsed    : constant LARGE_INTEGER :=

                         LARGE_INTEGER (Tick_Frequency / 100_000);

      --  Look for a precision of 0.01 ms

      Loc_Ticks, Ctrl_Ticks : aliased LARGE_INTEGER;

      Loc_Time, Ctrl_Time   : aliased Long_Long_Integer;

      Elapsed               : LARGE_INTEGER;

      Current_Max           : LARGE_INTEGER := LARGE_INTEGER'Last;

   begin

      --  Here we must be sure that both of these calls are done in a short

      --  amount of time. Both are base time and should in theory be taken

      --  at the very same time.

      --  The goal of the following loop is to synchronize the system time

      --  with the Win32 performance counter by getting a base offset for both.

      --  Using these offsets it is then possible to compute actual time using

      --  a performance counter which has a better precision than the Win32

      --  time API.

      --  Try at most 10th times to reach the best synchronisation (below 1

      --  millisecond) otherwise the runtime will use the best value reached

      --  during the runs.

      for K in 1 .. 10 loop

         if QueryPerformanceCounter (Loc_Ticks'Access) = Win32.FALSE then

            pragma Assert

              (Standard.False,

               "Could not query high performance counter in Clock");

            null;

         end if;

         GetSystemTimeAsFileTime (Ctrl_Time'Access);

         --  Scan for clock tick, will take upto 16ms/1ms depending on PC.

         --  This cannot be an infinite loop or the system hardware is badly

         --  dammaged.

         loop

            GetSystemTimeAsFileTime (Loc_Time'Access);

            if QueryPerformanceCounter (Ctrl_Ticks'Access) = Win32.FALSE then

               pragma Assert

                 (Standard.False,

                  "Could not query high performance counter in Clock");

               null;

            end if;

            exit when Loc_Time /= Ctrl_Time;

            Loc_Ticks := Ctrl_Ticks;

         end loop;

         --  Check elapsed Performance Counter between samples

         --  to choose the best one.

         Elapsed := Ctrl_Ticks - Loc_Ticks;

         if Elapsed < Current_Max then

            Base_Time   := Loc_Time;

            Base_Ticks  := Loc_Ticks;

            Current_Max := Elapsed;

            --  Exit the loop when we have reached the expected precision

            exit when Elapsed <= Max_Elapsed;

         end if;

      end loop;

      Base_Clock := Duration

        (Long_Long_Float ((Base_Time - epoch_1970) * system_time_ns) /

         Long_Long_Float (Sec_Unit));

   end Get_Base_Time;

   ---------------------

   -- Monotonic_Clock --

   ---------------------

   function Monotonic_Clock return Duration is

      Current_Ticks  : aliased LARGE_INTEGER;

      Elap_Secs_Tick : Duration;

   begin

      if QueryPerformanceCounter (Current_Ticks'Access) = Win32.FALSE then

         return 0.0;

      else

         Elap_Secs_Tick :=

           Duration (Long_Long_Float (Current_Ticks - BMTA.all) /

                       Long_Long_Float (TFA.all));

         return BMCA.all + Elap_Secs_Tick;

      end if;

   end Monotonic_Clock;

   -----------------

   -- Timed_Delay --

   -----------------

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

      function Mode_Clock return Duration;

      pragma Inline (Mode_Clock);

      --  Return the current clock value using either the monotonic clock or

      --  standard clock depending on the Mode value.

      ----------------

      -- Mode_Clock --

      ----------------

      function Mode_Clock return Duration is

      begin

         case Mode is

            when Absolute_RT =>

               return Monotonic_Clock;

            when others =>

               return Clock;

         end case;

      end Mode_Clock;

      --  Local Variables

      Base_Time : constant Duration := Mode_Clock;

      --  Base_Time is used to detect clock set backward, in this case we

      --  cannot ensure the delay accuracy.

      Rel_Time   : Duration;

      Abs_Time   : Duration;

      Check_Time : Duration := Base_Time;

   --  Start of processing for Timed Delay

   begin

      if Mode = Relative then

         Rel_Time := Time;

         Abs_Time := Time + Check_Time;

      else

         Rel_Time := Time - Check_Time;

         Abs_Time := Time;

      end if;

      if Rel_Time > 0.0 then

         loop

            Sleep (DWORD (Rel_Time * 1000.0));

            Check_Time := Mode_Clock;

            exit when Abs_Time <= Check_Time or else Check_Time < Base_Time;

            Rel_Time := Abs_Time - Check_Time;

         end loop;

      end if;

   end Timed_Delay;

   ----------------

   -- Initialize --

   ----------------

   Initialized : Boolean := False;

   procedure Initialize is

   begin

      if Initialized then

         return;

      end if;

      Initialized := True;

      --  Get starting time as base

      if QueryPerformanceFrequency (Tick_Frequency'Access) = Win32.FALSE then

         raise Program_Error with

           "cannot get high performance counter frequency";

      end if;

      Get_Base_Time;

      --  Keep base clock and ticks for the monotonic clock. These values

      --  should never be changed to ensure proper behavior of the monotonic

      --  clock.

      Base_Monotonic_Clock := Base_Clock;

      Base_Monotonic_Ticks := Base_Ticks;

   end Initialize;

end System.OS_Primitives;