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From: dennison@telepath.com
Subject: Re: Ada.Streams examples
Date: 1999/03/11
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 <7c64kl$r8s$1@nnrp1.dejanews.com> <36E6C291.F97766CB@Boeing.com>
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Date: 1999-03-11T00:00:00+00:00
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In article <36E7036B.EADEEA80@Boeing.com>,
  Rex Reges <Rex.R.Reges@Boeing.com> wrote:

> A container can be accessed by a single task at a time (only one packer at a
> time). However, two or more containers could be in the process of being filled
> at the same time, but only one task is allowed to do this work for any one
> container.  The honor system will be used, so a guard task isn't necessary.
>
> When the container is filled, then an exception should be raised. The choice
> then is to either use two containers or to use a bigger container.

Good. You are making things very easy for yourself. I needed something more
like a pipe, so it was considerably more difficult for me. All you'd have to
do in this case is create a simple buffer (an
Ada.Stream.Stream_Element_Array), and keep track of the read and write
pointers in the Stream's tagged type. I'd put a pointer to the buffer in the
stream type, and add a constructor procedure to allocate the array with a
given size and a destructor procedure to deallocate it:

private
   type Buffer_Ptr is access all Ada.Streams.Stream_Element_Array;
   type Stream is new Ada.Streams.Root_Stream_Type with record
      Head      : Index   := 1;
      Tail      : Index   := 1;
      Elements  : Buffer_Ptr;
   end record;


All you'd have to do after that is:  o	override "Write" to copy the given
stream elements into the buffer at the write pointer, and update the write
pointer.  o  override "Read" to copy the requested amount of stream elements
from the buffer at the read pointer, and update the read pointer.

If you wanted to get really sexy, I suppose you could implement "Open" calls
to prevent Reads from streams that are opened for Writes and the like.

T.E.D.

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