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Newsgroups: comp.lang.ada
Subject: Re: Impossible problem? A protected buffer to queue objects of a
  class-wide type
References: <461cc46d$1_1@glkas0286.greenlnk.net>
 <ilkp139uool31fc8opd7b94jpmctvndeg3@4ax.com>
  <461cd912$1_1@glkas0286.greenlnk.net>
From: Stephen Leake <stephen_leake@stephe-leake.org>
Date: Thu, 12 Apr 2007 04:36:11 -0400
Message-ID: <uy7kyng5g.fsf@stephe-leake.org>
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Date: 2007-04-12T04:36:11-04:00
List-Id: <comp.lang.ada>

"Phil Slater" <phil.slater@baesystems.com> writes:

> "Rob Norris" <firstname.lastname@baesystems.com> wrote in message 
> news:ilkp139uool31fc8opd7b94jpmctvndeg3@4ax.com...
>> >
>>>(b) To support this call, Dequeue must be written as a function. As such, 
>>>it
>>>cannot change the protected queue. What I need is the "entry" 
>>>functionality,
>>>since I want the Dequeue to wait if the queue is empty, and I want the 
>>>item
>>>to be removed from the queue as well as retrieved.
>>
>> Quick thought:
>> Is it possible to pass into the function a reference to the queue?
>> Then you should be able change the content of the queue as you see fit.
>>
>
> Maybe I didn't make myself clear. The queue is a protected object. 

Instead of making the queue itself a protected object, use a separate
protected object as a lock for the queue.

That is not quite as safe, but it will work.

> None of the three types of protected operation (functions,
> procedures and entries), does what I need. I need the
> barrier/blocking of an entry, I need write access to change the
> protected data (the queue), but I also need the operation to
> *return* a value (like a function does) so that it can be received
> in calling code by using it to initialise a newly declared variable
> of a class-wide type.

You could have a function take an access type, and allocate the user
object in the protected call. But you may have reasons for not wanting
to do that.

-- 
-- Stephe