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From: "DuckE" <nospam_steved94@home.com>
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 <3BB56747.D60CA49F@acm.org>
Subject: Re: Question on using protected objects
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Date: Sat, 29 Sep 2001 12:30:26 GMT
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"Jeffrey Carter" <jrcarter@acm.org> wrote in message
news:3BB56747.D60CA49F@acm.org...
> What does your compiler say? (Hint: I suggest using GNAT with the -gnaty
> option.)

The compiler is perfectly happy with this.  It even "appears" to do exactly
what I want.  If I were programming in C, that's as far as I would go before
using this construct.  In Ada I try to avoid the "try it and see if it
works" mode of operation since it sometimes leads to unpredictable results.

Here is the complete test program that "appears" do do exactly what I want,
I just don't know whether it is appropriate to use the "defining_identifier"
as part of the "entry_barrier" (LRM 9.5.2):

WITH Ada.Text_Io;

PROCEDURE TestProtType IS

  nbWaiters : CONSTANT := 4;

  SUBTYPE aWaitSelect IS INTEGER RANGE 1 .. nbWaiters;

  TYPE aWaitArray IS ARRAY( aWaitSelect ) OF BOOLEAN;

  PROTECTED TYPE aQueueingType IS
    ENTRY GetEntry( waitSelect  : aWaitSelect; getResult : out Integer );
    PROCEDURE Release( waitSelect  : aWaitSelect );
  PRIVATE
    ENTRY WaitForIt( aWaitSelect );
    waitFlag : aWaitArray := ( OTHERS => FALSE );
    counter  : Natural := 0;
  END aQueueingType;

  PROTECTED BODY aQueueingType IS
    PROCEDURE Release( waitSelect : aWaitSelect ) IS
    BEGIN
      waitFlag( waitSelect  ) := TRUE;
    END Release;
    ENTRY GetEntry( waitSelect : aWaitSelect;
                     getResult : out Integer ) WHEN GetEntry'COUNT = 0 IS
    BEGIN
      getResult := counter;
      counter := counter + 1;
      REQUEUE WaitForIt( waitSelect );
    END GetEntry;
    ENTRY WaitForIt ( FOR waitSelect IN aWaitSelect )
         WHEN waitFlag( waitSelect ) IS
    BEGIN
      waitFlag( waitSelect ) := FALSE;
    END WaitForIt;
  END aQueueingType;

  qFlag : aQueueingType;

  TASK TYPE aWaiter( waitSelect : aWaitSelect ) IS
  END aWaiter;

  TASK BODY aWaiter IS
    getResult : Integer;
  BEGIN
    qFlag.GetEntry( waitSelect, getResult );
    Ada.Text_Io.Put_Line( "Waiter " &
                          aWaitSelect'IMAGE(waitSelect) &
                          ", " & Integer'IMAGE( getResult ) &
                          " released!" );
  END aWaiter;

  TYPE aWaiterPtr IS ACCESS ALL aWaiter;
  nbWaitTasks : CONSTANT := 3;

BEGIN
  FOR lpCnt IN 1 .. nbWaitTasks LOOP
    FOR ii IN aWaitSelect'RANGE LOOP
      DECLARE
        waitPtr : aWaiterPtr;
      BEGIN
        waitPtr := NEW aWaiter( ii );
      END;
    END LOOP;
  END LOOP;
  FOR lpCnt IN 1 .. nbWaitTasks LOOP
    FOR ii IN aWaitSelect'RANGE LOOP
      DELAY 1.0;
      qFlag.Release( ii );
    END LOOP;
  END LOOP;
  DELAY 1.0;
END TestProtType;

>
> --
> Jeff Carter
> "You cheesy lot of second-hand electric donkey-bottom biters."
> Monty Python & the Holy Grail