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-- --
-- --
-- S Y S T E M . O S _ P R I M I T I V E S --
-- --
-- B o d y --
-- --
-- Copyright (C) 1998-2021, 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 --
-- --
-- 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 --
-- <>. --
-- --
-- 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.Task_Lock;
with System.Win32.Ext;
package body System.OS_Primitives is
use System.Task_Lock;
use System.Win32;
use System.Win32.Ext;
-- Data for the high resolution clock --
Tick_Frequency : aliased LARGE_INTEGER;
-- Holds frequency of high-performance counter used by Clock
-- Windows NT uses a 1_193_182 Hz counter on PCs.
Base_Monotonic_Ticks : LARGE_INTEGER;
-- Holds the Tick count for the base monotonic time
Base_Monotonic_Clock : Duration;
-- Holds the current clock for monotonic clock's base time
type Clock_Data is record
-- Holds the Tick count for the base time
Base_Time : Long_Long_Integer;
-- Holds the base time used to check for system time change, used with
-- the standard clock.
Base_Clock : Duration;
-- Holds the current clock for the standard clock's base time
end record;
type Clock_Data_Access is access all Clock_Data;
-- Two base clock buffers. This is used to be able to update a buffer while
-- the other buffer is read. The point is that we do not want to use a lock
-- inside the Clock routine for performance reasons. We still use a lock
-- in the Get_Base_Time which is called very rarely. Current is a pointer,
-- the pragma Atomic is there to ensure that the value can be set or read
-- atomically. That's it, when Get_Base_Time has updated a buffer the
-- switch to the new value is done by changing Current pointer.
First, Second : aliased Clock_Data;
Current : Clock_Data_Access := First'Access;
pragma Atomic (Current);
-- The following signature is to detect change on the base clock data
-- above. The signature is a modular type, it will wrap around without
-- raising an exception. We would need to have exactly 2**32 updates of
-- the base data for the changes to get undetected.
type Signature_Type is mod 2**32;
Signature : Signature_Type := 0;
pragma Atomic (Signature);
function Monotonic_Clock return Duration;
pragma Export (Ada, Monotonic_Clock, "__gnat_monotonic_clock");
-- Return "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. Export this function so that it
-- can be imported from s-taprop-mingw.adb without changing the shared
-- spec (
procedure Get_Base_Time (Data : in out Clock_Data);
-- 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;
Data : Clock_Data;
Current_Ticks : aliased LARGE_INTEGER;
Elap_Secs_Tick : Duration;
Elap_Secs_Sys : Duration;
Now : aliased Long_Long_Integer;
Sig1, Sig2 : Signature_Type;
-- Try ten times to get a coherent set of base data. For this we just
-- check that the signature hasn't changed during the copy of the
-- current data.
-- This loop will always be done once if there is no interleaved call
-- to Get_Base_Time.
for K in 1 .. 10 loop
Sig1 := Signature;
Data := Current.all;
Sig2 := Signature;
exit when Sig1 = Sig2;
end loop;
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 - Data.Base_Time)) /
Elap_Secs_Tick :=
Duration (Long_Long_Float (Current_Ticks - Data.Base_Ticks) /
Long_Long_Float (Tick_Frequency));
-- If we have a shift of more than Max_Shift seconds we resynchronize
-- the Clock. This is probably due to a manual Clock adjustment, a 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 (Data);
Elap_Secs_Tick :=
Duration (Long_Long_Float (Current_Ticks - Data.Base_Ticks) /
Long_Long_Float (Tick_Frequency));
end if;
return Data.Base_Clock + Elap_Secs_Tick;
end Clock;
-- Get_Base_Time --
procedure Get_Base_Time (Data : in out Clock_Data) 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
Sig : constant Signature_Type := Signature;
Loc_Ticks, Ctrl_Ticks : aliased LARGE_INTEGER;
Loc_Time, Ctrl_Time : aliased Long_Long_Integer;
New_Data : Clock_Data_Access;
-- 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 10 times to reach the best synchronisation (below 1
-- millisecond) otherwise the runtime will use the best value reached
-- during the runs.
-- First check that the current value has not been updated. This
-- could happen if another task has called Clock at the same time
-- and that Max_Shift has been reached too.
-- But if the current value has been changed just before we entered
-- into the critical section, we can safely return as the current
-- base data (time, clock, ticks) have already been updated.
if Sig /= Signature then
end if;
-- Check for the unused data buffer and set New_Data to point to it
if Current = First'Access then
New_Data := Second'Access;
New_Data := First'Access;
end if;
for K in 1 .. 10 loop
if QueryPerformanceCounter (Loc_Ticks'Access) = Win32.FALSE then
pragma Assert
"Could not query high performance counter in Clock");
end if;
GetSystemTimeAsFileTime (Ctrl_Time'Access);
-- Scan for clock tick, will take up to 16ms/1ms depending on PC.
-- This cannot be an infinite loop or the system hardware is badly
-- damaged.
GetSystemTimeAsFileTime (Loc_Time'Access);
if QueryPerformanceCounter (Ctrl_Ticks'Access) = Win32.FALSE then
pragma Assert
"Could not query high performance counter in Clock");
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
New_Data.Base_Time := Loc_Time;
New_Data.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;
New_Data.Base_Clock :=
((New_Data.Base_Time - epoch_1970) * system_time_ns) /
Long_Long_Float (Sec_Unit));
-- At this point all the base values have been set into the new data
-- record. Change the pointer (atomic operation) to these new values.
Current := New_Data;
Data := New_Data.all;
-- Set new signature for this data set
Signature := Signature + 1;
when others =>
end Get_Base_Time;
-- Monotonic_Clock --
function Monotonic_Clock return Duration is
Current_Ticks : aliased LARGE_INTEGER;
Elap_Secs_Tick : Duration;
if QueryPerformanceCounter (Current_Ticks'Access) = Win32.FALSE then
return 0.0;
Elap_Secs_Tick :=
Duration (Long_Long_Float (Current_Ticks - Base_Monotonic_Ticks) /
Long_Long_Float (Tick_Frequency));
return Base_Monotonic_Clock + 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
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
if Mode = Relative then
Rel_Time := Time;
Abs_Time := Time + Check_Time;
Rel_Time := Time - Check_Time;
Abs_Time := Time;
end if;
if Rel_Time > 0.0 then
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
if Initialized then
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 (Current.all);
-- 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 := Current.Base_Clock;
Base_Monotonic_Ticks := Current.Base_Ticks;
end Initialize;
end System.OS_Primitives;