417 lines
15 KiB
Ada
417 lines
15 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
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-- --
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-- S Y S T E M . O S _ P R I M I T I V E S --
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-- --
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-- B o d y --
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-- --
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-- Copyright (C) 1998-2015, Free Software Foundation, Inc. --
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-- --
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-- GNARL is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNARL was developed by the GNARL team at Florida State University. --
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-- Extensive contributions were provided by Ada Core Technologies, Inc. --
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-- --
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------------------------------------------------------------------------------
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-- This is the NT version of this package
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with System.Task_Lock;
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with System.Win32.Ext;
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package body System.OS_Primitives is
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use System.Task_Lock;
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use System.Win32;
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use System.Win32.Ext;
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----------------------------------------
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-- Data for the high resolution clock --
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----------------------------------------
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Tick_Frequency : aliased LARGE_INTEGER;
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-- Holds frequency of high-performance counter used by Clock
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-- Windows NT uses a 1_193_182 Hz counter on PCs.
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Base_Monotonic_Ticks : LARGE_INTEGER;
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-- Holds the Tick count for the base monotonic time
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Base_Monotonic_Clock : Duration;
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-- Holds the current clock for monotonic clock's base time
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type Clock_Data is record
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Base_Ticks : LARGE_INTEGER;
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-- Holds the Tick count for the base time
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Base_Time : Long_Long_Integer;
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-- Holds the base time used to check for system time change, used with
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-- the standard clock.
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Base_Clock : Duration;
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-- Holds the current clock for the standard clock's base time
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end record;
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type Clock_Data_Access is access all Clock_Data;
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-- Two base clock buffers. This is used to be able to update a buffer while
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-- the other buffer is read. The point is that we do not want to use a lock
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-- inside the Clock routine for performance reasons. We still use a lock
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-- in the Get_Base_Time which is called very rarely. Current is a pointer,
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-- the pragma Atomic is there to ensure that the value can be set or read
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-- atomically. That's it, when Get_Base_Time has updated a buffer the
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-- switch to the new value is done by changing Current pointer.
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First, Second : aliased Clock_Data;
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Current : Clock_Data_Access := First'Access;
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pragma Atomic (Current);
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-- The following signature is to detect change on the base clock data
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-- above. The signature is a modular type, it will wrap around without
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-- raising an exception. We would need to have exactly 2**32 updates of
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-- the base data for the changes to get undetected.
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type Signature_Type is mod 2**32;
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Signature : Signature_Type := 0;
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pragma Atomic (Signature);
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function Monotonic_Clock return Duration;
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pragma Export (Ada, Monotonic_Clock, "__gnat_monotonic_clock");
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-- Return "absolute" time, represented as an offset relative to "the Unix
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-- Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is
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-- immune to the system's clock changes. Export this function so that it
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-- can be imported from s-taprop-mingw.adb without changing the shared
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-- spec (s-osprim.ads).
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procedure Get_Base_Time (Data : in out Clock_Data);
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-- Retrieve the base time and base ticks. These values will be used by
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-- clock to compute the current time by adding to it a fraction of the
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-- performance counter. This is for the implementation of a high-resolution
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-- clock. Note that this routine does not change the base monotonic values
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-- used by the monotonic clock.
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-----------
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-- Clock --
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-----------
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-- This implementation of clock provides high resolution timer values
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-- using QueryPerformanceCounter. This call return a 64 bits values (based
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-- on the 8253 16 bits counter). This counter is updated every 1/1_193_182
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-- times per seconds. The call to QueryPerformanceCounter takes 6
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-- microsecs to complete.
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function Clock return Duration is
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Max_Shift : constant Duration := 2.0;
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Hundreds_Nano_In_Sec : constant Long_Long_Float := 1.0E7;
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Data : Clock_Data;
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Current_Ticks : aliased LARGE_INTEGER;
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Elap_Secs_Tick : Duration;
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Elap_Secs_Sys : Duration;
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Now : aliased Long_Long_Integer;
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Sig1, Sig2 : Signature_Type;
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begin
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-- Try ten times to get a coherent set of base data. For this we just
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-- check that the signature hasn't changed during the copy of the
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-- current data.
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--
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-- This loop will always be done once if there is no interleaved call
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-- to Get_Base_Time.
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for K in 1 .. 10 loop
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Sig1 := Signature;
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Data := Current.all;
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Sig2 := Signature;
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exit when Sig1 = Sig2;
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end loop;
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if QueryPerformanceCounter (Current_Ticks'Access) = Win32.FALSE then
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return 0.0;
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end if;
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GetSystemTimeAsFileTime (Now'Access);
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Elap_Secs_Sys :=
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Duration (Long_Long_Float (abs (Now - Data.Base_Time)) /
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Hundreds_Nano_In_Sec);
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Elap_Secs_Tick :=
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Duration (Long_Long_Float (Current_Ticks - Data.Base_Ticks) /
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Long_Long_Float (Tick_Frequency));
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-- If we have a shift of more than Max_Shift seconds we resynchronize
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-- the Clock. This is probably due to a manual Clock adjustment, a DST
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-- adjustment or an NTP synchronisation. And we want to adjust the time
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-- for this system (non-monotonic) clock.
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if abs (Elap_Secs_Sys - Elap_Secs_Tick) > Max_Shift then
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Get_Base_Time (Data);
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Elap_Secs_Tick :=
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Duration (Long_Long_Float (Current_Ticks - Data.Base_Ticks) /
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Long_Long_Float (Tick_Frequency));
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end if;
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return Data.Base_Clock + Elap_Secs_Tick;
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end Clock;
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-------------------
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-- Get_Base_Time --
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-------------------
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procedure Get_Base_Time (Data : in out Clock_Data) is
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-- The resolution for GetSystemTime is 1 millisecond
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-- The time to get both base times should take less than 1 millisecond.
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-- Therefore, the elapsed time reported by GetSystemTime between both
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-- actions should be null.
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epoch_1970 : constant := 16#19D_B1DE_D53E_8000#; -- win32 UTC epoch
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system_time_ns : constant := 100; -- 100 ns per tick
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Sec_Unit : constant := 10#1#E9;
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Max_Elapsed : constant LARGE_INTEGER :=
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LARGE_INTEGER (Tick_Frequency / 100_000);
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-- Look for a precision of 0.01 ms
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Sig : constant Signature_Type := Signature;
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Loc_Ticks, Ctrl_Ticks : aliased LARGE_INTEGER;
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Loc_Time, Ctrl_Time : aliased Long_Long_Integer;
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Elapsed : LARGE_INTEGER;
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Current_Max : LARGE_INTEGER := LARGE_INTEGER'Last;
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New_Data : Clock_Data_Access;
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begin
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-- Here we must be sure that both of these calls are done in a short
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-- amount of time. Both are base time and should in theory be taken
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-- at the very same time.
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-- The goal of the following loop is to synchronize the system time
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-- with the Win32 performance counter by getting a base offset for both.
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-- Using these offsets it is then possible to compute actual time using
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-- a performance counter which has a better precision than the Win32
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-- time API.
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-- Try at most 10 times to reach the best synchronisation (below 1
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-- millisecond) otherwise the runtime will use the best value reached
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-- during the runs.
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Lock;
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-- First check that the current value has not been updated. This
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-- could happen if another task has called Clock at the same time
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-- and that Max_Shift has been reached too.
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--
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-- But if the current value has been changed just before we entered
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-- into the critical section, we can safely return as the current
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-- base data (time, clock, ticks) have already been updated.
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if Sig /= Signature then
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Unlock;
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return;
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end if;
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-- Check for the unused data buffer and set New_Data to point to it
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if Current = First'Access then
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New_Data := Second'Access;
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else
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New_Data := First'Access;
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end if;
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for K in 1 .. 10 loop
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if QueryPerformanceCounter (Loc_Ticks'Access) = Win32.FALSE then
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pragma Assert
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(Standard.False,
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"Could not query high performance counter in Clock");
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null;
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end if;
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GetSystemTimeAsFileTime (Ctrl_Time'Access);
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-- Scan for clock tick, will take up to 16ms/1ms depending on PC.
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-- This cannot be an infinite loop or the system hardware is badly
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-- damaged.
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loop
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GetSystemTimeAsFileTime (Loc_Time'Access);
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if QueryPerformanceCounter (Ctrl_Ticks'Access) = Win32.FALSE then
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pragma Assert
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(Standard.False,
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"Could not query high performance counter in Clock");
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null;
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end if;
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exit when Loc_Time /= Ctrl_Time;
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Loc_Ticks := Ctrl_Ticks;
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end loop;
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-- Check elapsed Performance Counter between samples
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-- to choose the best one.
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Elapsed := Ctrl_Ticks - Loc_Ticks;
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if Elapsed < Current_Max then
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New_Data.Base_Time := Loc_Time;
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New_Data.Base_Ticks := Loc_Ticks;
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Current_Max := Elapsed;
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-- Exit the loop when we have reached the expected precision
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exit when Elapsed <= Max_Elapsed;
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end if;
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end loop;
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New_Data.Base_Clock :=
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Duration
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(Long_Long_Float
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((New_Data.Base_Time - epoch_1970) * system_time_ns) /
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Long_Long_Float (Sec_Unit));
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-- At this point all the base values have been set into the new data
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-- record. Change the pointer (atomic operation) to these new values.
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Current := New_Data;
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Data := New_Data.all;
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-- Set new signature for this data set
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Signature := Signature + 1;
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Unlock;
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exception
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when others =>
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Unlock;
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raise;
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end Get_Base_Time;
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---------------------
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-- Monotonic_Clock --
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---------------------
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function Monotonic_Clock return Duration is
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Current_Ticks : aliased LARGE_INTEGER;
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Elap_Secs_Tick : Duration;
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begin
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if QueryPerformanceCounter (Current_Ticks'Access) = Win32.FALSE then
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return 0.0;
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else
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Elap_Secs_Tick :=
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Duration (Long_Long_Float (Current_Ticks - Base_Monotonic_Ticks) /
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Long_Long_Float (Tick_Frequency));
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return Base_Monotonic_Clock + Elap_Secs_Tick;
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end if;
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end Monotonic_Clock;
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-----------------
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-- Timed_Delay --
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-----------------
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procedure Timed_Delay (Time : Duration; Mode : Integer) is
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function Mode_Clock return Duration;
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pragma Inline (Mode_Clock);
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-- Return the current clock value using either the monotonic clock or
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-- standard clock depending on the Mode value.
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----------------
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-- Mode_Clock --
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----------------
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function Mode_Clock return Duration is
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begin
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case Mode is
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when Absolute_RT =>
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return Monotonic_Clock;
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when others =>
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return Clock;
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end case;
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end Mode_Clock;
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-- Local Variables
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Base_Time : constant Duration := Mode_Clock;
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-- Base_Time is used to detect clock set backward, in this case we
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-- cannot ensure the delay accuracy.
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Rel_Time : Duration;
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Abs_Time : Duration;
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Check_Time : Duration := Base_Time;
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-- Start of processing for Timed Delay
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begin
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if Mode = Relative then
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Rel_Time := Time;
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Abs_Time := Time + Check_Time;
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else
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Rel_Time := Time - Check_Time;
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Abs_Time := Time;
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end if;
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if Rel_Time > 0.0 then
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loop
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Sleep (DWORD (Rel_Time * 1000.0));
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Check_Time := Mode_Clock;
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exit when Abs_Time <= Check_Time or else Check_Time < Base_Time;
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Rel_Time := Abs_Time - Check_Time;
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end loop;
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end if;
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end Timed_Delay;
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----------------
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-- Initialize --
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----------------
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Initialized : Boolean := False;
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procedure Initialize is
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begin
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if Initialized then
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return;
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end if;
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Initialized := True;
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-- Get starting time as base
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if QueryPerformanceFrequency (Tick_Frequency'Access) = Win32.FALSE then
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raise Program_Error with
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"cannot get high performance counter frequency";
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end if;
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Get_Base_Time (Current.all);
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-- Keep base clock and ticks for the monotonic clock. These values
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-- should never be changed to ensure proper behavior of the monotonic
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-- clock.
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Base_Monotonic_Clock := Current.Base_Clock;
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Base_Monotonic_Ticks := Current.Base_Ticks;
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end Initialize;
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end System.OS_Primitives;
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