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-- C940002.A
--
--
--                             Grant of Unlimited Rights
--
--     Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687,
--     F08630-91-C-0015, and DCA100-97-D-0025, the U.S. Government obtained 
--     unlimited rights in the software and documentation contained herein.
--     Unlimited rights are defined in DFAR 252.227-7013(a)(19).  By making 
--     this public release, the Government intends to confer upon all 
--     recipients unlimited rights  equal to those held by the Government.  
--     These rights include rights to use, duplicate, release or disclose the 
--     released technical data and computer software in whole or in part, in 
--     any manner and for any purpose whatsoever, and to have or permit others 
--     to do so.
--
--                                    DISCLAIMER
--
--     ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR
--     DISCLOSED ARE AS IS.  THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED 
--     WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE
--     SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE 
--     OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A
--     PARTICULAR PURPOSE OF SAID MATERIAL.
--*
--
-- OBJECTIVE:
--      Check that a protected object provides coordinated access to shared 
--      data.  Check that it can implement a semaphore-like construct using a
--      parameterless procedure which allows a specific maximum number of tasks
--      to run and excludes all others
--
-- TEST DESCRIPTION:
--      Implement a counting semaphore type that can be initialized to a 
--      specific number of available resources.  Declare an entry for 
--      requesting a resource and a procedure for releasing it.  Declare an 
--      object of this type, initialized to two resources.  Declare and start 
--      three tasks each of which asks for a resource.  Verify that only two 
--      resources are granted and that the last task in is queued.
--
--
-- CHANGE HISTORY:
--      06 Dec 94   SAIC    ACVC 2.0
--
--!


package C940002_0 is
     -- Semaphores

  protected type Semaphore_Type (Resources_Available : Integer :=1) is
    entry Request;
    procedure Release;
    function Available return Integer;
  private
    Currently_Available : Integer := Resources_Available;
  end Semaphore_Type;

  Max_Resources : constant Integer := 2;
  Resource      : Semaphore_Type (Max_Resources);

end C940002_0;
 -- Semaphores;


          --========================================================--


package body C940002_0 is
          -- Semaphores

  protected body Semaphore_Type is

    entry Request when Currently_Available >0 is  -- when granted, secures
    begin                                         -- a resource
      Currently_Available := Currently_Available - 1;
    end Request;

    procedure Release is                          -- when called, releases
    begin                                         -- a resource
      Currently_Available := Currently_Available + 1;
    end Release;

    function Available return Integer is          -- returns number of
    begin                                         -- available resources
      return Currently_Available;
    end Available;

  end Semaphore_Type;

end C940002_0;
 -- Semaphores;


          --========================================================--


package C940002_1 is
     -- Task_Pkg

  task type Requesting_Task is
     entry Done;                        -- call on Done instructs the task
  end Requesting_Task;                  -- to release resource

  type Task_Ptr is access Requesting_Task;

  protected Counter is
    procedure Increment;
    procedure Decrement;
    function Number return integer;
  private
    Count : Integer := 0;
  end Counter;

  protected Hold_Lock is
    procedure Lock;
    procedure Unlock;
    function  Locked return Boolean;
  private
    Lock_State  : Boolean := true;        -- starts out locked
  end Hold_Lock;


end C940002_1;
 -- Task_Pkg


          --========================================================--


with Report;
with C940002_0;
  -- Semaphores;    

package body C940002_1 is
          -- Task_Pkg is
  
  protected body Counter is

    procedure Increment is
      begin
        Count := Count + 1;
      end Increment;

    procedure Decrement is
      begin
        Count := Count - 1;
      end Decrement;

    function Number return Integer is
      begin
        return Count;
      end Number;

  end Counter;


  protected body Hold_Lock is

    procedure Lock is 
    begin
      Lock_State := true;
    end Lock;

    procedure Unlock is 
    begin
      Lock_State := false;
    end Unlock;

    function  Locked return Boolean is 
    begin
      return Lock_State;
    end Locked;

  end Hold_Lock;


  task body Requesting_Task is
  begin
    C940002_0.Resource.Request;        -- request a resource
                                       -- if resource is not available, 
                                       -- task will be queued to wait
    Counter.Increment;                 -- add to count of resources obtained
    Hold_Lock.Unlock;                  -- and unlock Lock - system is stable;
                                       -- status may now be queried

    accept Done do                     -- hold resource until Done is called
      C940002_0.Resource.Release;      -- release the resource and
      Counter.Decrement;               -- note release
    end Done;                           

  exception
    when others => Report.Failed ("Unexpected Exception in Requesting_Task");
  end Requesting_Task;

end C940002_1;
 -- Task_Pkg;


          --========================================================--


with Report;
with ImpDef;
with C940002_0,
  -- Semaphores, 
     C940002_1;
  -- Task_Pkg;

procedure C940002 is

  package Semaphores renames C940002_0;
  package Task_Pkg renames C940002_1;

  Ptr1,
  Ptr2, 
  Ptr3 : Task_Pkg.Task_Ptr;
  Num  : Integer;

  procedure Spinlock is
    begin
      -- loop until unlocked
      while Task_Pkg.Hold_Lock.Locked loop
        delay ImpDef.Minimum_Task_Switch;   
      end loop;
      Task_Pkg.Hold_Lock.Lock;
    end Spinlock;

begin

  Report.Test ("C940002", "Check that a protected record can be used to " &
                          "control access to resources");

  if (Task_Pkg.Counter.Number /=0)
  or (Semaphores.Resource.Available /= 2) then
    Report.Failed ("Wrong initial conditions");
  end if;
                                  
  Ptr1 := new Task_Pkg.Requesting_Task;   -- newly allocated task requests 
                                   -- resource; request for resource should 
                                   -- be granted
  Spinlock;                        -- ensure that task obtains resource

                                   -- Task 1 waiting for call to Done
                                   -- One resource assigned to task 1
                                   -- One resource still available
  if (Task_Pkg.Counter.Number /= 1) 
  or (Semaphores.Resource.Available /= 1) then
    Report.Failed ("Resource not assigned to task 1");
  end if;

  Ptr2 := new Task_Pkg.Requesting_Task;   -- newly allocated task requests 
                                   -- resource; request for resource should 
                                   -- be granted
  Spinlock;                        -- ensure that task obtains resource  

                                   -- Task 1 waiting for call to Done
                                   -- Task 2 waiting for call to Done
                                   -- Resources held by tasks 1 and 2
                                   -- No resources available
  if (Task_Pkg.Counter.Number /= 2) 
  or (Semaphores.Resource.Available /= 0) then
    Report.Failed ("Resource not assigned to task 2");
  end if;

  Ptr3 := new Task_Pkg.Requesting_Task;   -- newly allocated task requests 
                                   -- resource; request for resource should 
                                   -- be denied and task queued to wait for 
                                   -- next available resource


  Ptr1.all.Done;                   -- Task 1 releases resource and lock
                                   -- Resource should be given to queued task
  Spinlock;                        -- ensure that resource is released


                                   -- Task 1 holds no resource
                                   -- One resource still assigned to task 2
                                   -- One resource assigned to task 3
                                   -- No resources available
  if (Task_Pkg.Counter.Number /= 2) 
  or (Semaphores.Resource.Available /= 0) then
    Report.Failed ("Resource not properly released/assigned to task 3");
  end if;

  Ptr2.all.Done;                   -- Task 2 releases resource and lock
                                   -- No outstanding request for resource

                                   -- Tasks 1 and 2 hold no resources
                                   -- One resource assigned to task 3
                                   -- One resource available
  if (Task_Pkg.Counter.Number /= 1)
  or (Semaphores.Resource.Available /= 1) then 
    Report.Failed ("Resource not properly released from task 2");
  end if;

  Ptr3.all.Done;                   -- Task 3 releases resource and lock

                                   -- All resources released
                                   -- All tasks terminated (or close)
                                   -- Two resources available
  if (Task_Pkg.Counter.Number /=0) 
  or (Semaphores.Resource.Available /= 2) then 
    Report.Failed ("Resource not properly released from task 3");
  end if;

  Report.Result;

end C940002;