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From: dmitry@elros.cbb-automation.de (Dmitry A. Kazakov)
Newsgroups: comp.lang.ada
Subject: How to avoid unreferenced objects (mutexes etc)
Date: Fri, 11 Jan 2002 13:48:15 GMT
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Date: 2002-01-11T13:48:15+00:00
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Hi all!

I have a question.

Let I implement mutex and locking objects as follows:

protected type Mutex is
   entry Seize;
   procedure Release;
private
   Owned : Boolean := False;
end Mutex;

type Lock (Resource : access Mutex) is new
   Ada.Finalization.Limited_Controlled with null record;
procedure Initialize (Object : in out Lock) is
begin
   Object.Resource.Seize;
end Initialize;
procedure Finalize (Object : in out Lock) is
begin
   Object.Resource.Release;
end Finalize;

The idea is to write critical sections as follows:

   Temp : Lock (Mutex_of_a_resource'Access);
begin
   ...  -- Safe access to the resource
end; -- Mutex is released even if an exception propagates

The problem is that the object Temp is never referenced. The compiler
complains of that, but it is a minor problem. The questions are

1. Has the compiler right to optimize out Temp?
2. Is there a better solution?

Thanks,
Dmitry Kazakov