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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: Combining entry_call, accept_statment and terminate_statment
Date: Tue, 30 Mar 2004 22:47:27 +0000 (UTC)
Organization: IKS GmbH Jena
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* Randy Brukardt wrote:
> "Lutz Donnerhacke" <lutz@iks-jena.de> wrote in message
>> That's exactly my current implementation. But I increased the delay and
>> noticed, that the entry_barrier of the delayed entry_call is evaluated
>> only once on startup of the timed entry call. If the barrier becomes
>> true while the delay is running, the delay is not aborted.
>>
>> A reason for this strange behavior might be a call to a protected function
>> in the entry_barrier itself.
>
> Barriers of a PO are re-evaluated whenever a protected action ends, and when
> an entry is called. A barrier which can change state without a protected
> action ending is incorrect and may not work properly.

So cascading of protected types will not work.

My incorrect version was:

   protected type Ringbuffer is
      procedure Put(data : in String);
      procedure Get(data : out Buffer; last : out Extended_Buffer_Offset;
        missed : out Absolute_Position; pos : in out Absolute_Position);
      function Is_New(pos : Absolute_Position) return Boolean;
   private
      buf : Buffer;
      start, stop : Absolute_Position := Absolute_Position'First;
   end Ringbuffer;
   
   protected type Read_Context(ringbuf : access Ringbuffer) is
      entry Get(data : out Buffer; last : out Extended_Buffer_Offset;
        missed : out Absolute_Position);
   private
      pos : Absolute_Position := Absolute_Position'First;
   end Read_Context;

   protected body Read_Context is
      entry Get(
        data : out Buffer; last : out Extended_Buffer_Offset;
        missed : out Absolute_Position
      ) when ringbuf.Is_New(pos) is
      begin
         ringbuf.Get(data, last, missed, pos);
      end Get;
   end Read_Context;