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-- C960002.A

--

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--*

--

-- OBJECTIVE:

--      Check that the simple "delay until" when the request time is "now" and

--      also some time already in the past is obeyed and returns immediately

--

-- TEST DESCRIPTION:

--      Simulate a task that sends a "pulse" at regular intervals.  The Delay

--      Until statement is used to avoid accumulated drift.  In this test

--      three simple situations simulating the start of drift are used:  the

--      next pulse being called for at the normal time, the next pulse being

--      called for at exactly the current time and then at some time which has

--      already past.  We assume the delay is within a While Loop and, to

--      simplify the test, we "unfold" the While Loop and  execute the Delays

--      in a serial fashion.  This loop is shown in test C960001.

--      It is not possible to test the actual immediacy of the expiration. We

--      can only check that it returns in a "reasonable" time.  In this case

--      we check that it expires before the next "pulse" should have been

--      issued.

--

--

-- CHANGE HISTORY:

--      06 Dec 94   SAIC    ACVC 2.0

--

--!

with Report;

with ImpDef;

with Ada.Calendar;

with System;

procedure C960002 is

begin

   Report.Test ("C960002", "Simple Delay Until with requested time being" &

                        " ""now"" and time already in the past");

   declare  -- To get the Report.Result after all has completed

      function "+" (Left : Ada.Calendar.Time; Right: Duration)

                            return Ada.Calendar.Time renames Ada.Calendar."+";

      function "-" (Left : Ada.Calendar.Time; Right: Duration)

                            return Ada.Calendar.Time renames Ada.Calendar."-";

      function "-" (Left, Right : Ada.Calendar.Time)

                            return duration      renames Ada.Calendar."-";

      function ">" (Left, Right : Ada.Calendar.Time)

                            return Boolean       renames Ada.Calendar.">";

      task Pulse_Task is

         entry Trigger;

      end Pulse_Task;

      -- Task to synchronize all qualified receivers.

      -- The entry Trigger starts the synchronization.

      --

      task body Pulse_Task is

         Pulse_Time       : Ada.Calendar.Time;

         Pulse_Time_Delta : constant duration := ImpDef.Clear_Ready_Queue;

         TC_Time_Back     : Ada.Calendar.Time;

         -- This routine transmits a synchronizing "pulse" to

         -- all receivers

         procedure Pulse is

         begin

            null;  -- Stub

            Report.Comment (".......PULSE........");

         end Pulse;

      begin

         accept Trigger;

         Pulse;

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

         -- normal calculation for "next"

         Pulse_Time := Ada.Calendar.Clock + Pulse_Time_Delta;

         -- TC:  unfold the "while" loop in C960001.  Four passes through

         -- the loop are shown

            delay until Pulse_Time;

            Pulse;

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

            -- TC: the normal calculation for "next" would be

            -- Pulse_Time := Pulse_Time + Pulse_Time_Delta;

            -- Instead of this normal pulse time calculation simulate

            -- the new pulse time to be exactly "now"  (or, as exactly as

            -- we can)

            Pulse_Time := Ada.Calendar.Clock;

            delay until  Ada.Calendar.Clock;

            TC_Time_Back := Ada.Calendar.Clock;

            -- Now check for reasonableness

            if TC_Time_Back > Pulse_Time + Pulse_Time_Delta then

               Report.Failed

                     ("""Now"" delayed for more than Pulse_Time_Delta - A");

            end if;

            Pulse;

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

            -- normal calculation for "next" would be

            Pulse_Time := Pulse_Time + Pulse_Time_Delta;

            -- TC: Instead of this, simulate the new calculated pulse time

            -- being already past

            Pulse_Time := Ada.Calendar.Clock - System.Tick;

            delay until Pulse_Time;

            TC_Time_Back := Ada.Calendar.Clock;

            -- Now check for reasonableness

            if TC_Time_Back > Pulse_Time + Pulse_Time_Delta then

               Report.Failed

                     ("""Now"" delayed for more than Pulse_Time_Delta - B");

            end if;

            Pulse;

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

            -- normal calculation for "next"

            Pulse_Time := Pulse_Time + Pulse_Time_Delta;

            -- Now simulate getting back into synch

            delay until Pulse_Time;

            Pulse;

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

         -- This would be the end of the "while" loop

      exception

         when others =>

               Report.Failed ("Unexpected exception in Pulse_Task");

      end Pulse_Task;

   begin -- declare

      Pulse_Task.Trigger;      -- Start test

   end; -- declare

   Report.Result;

end C960002;