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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Software landmines (loops)
Date: 1998/09/02
Message-ID: <m3ogsz74as.fsf@mheaney.ni.net>#1/1
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NNTP-Posting-Date: Wed, 02 Sep 1998 00:15:46 PDT
Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada
Date: 1998-09-02T00:00:00+00:00
List-Id: <comp.lang.ada>

"Robert Martin" <rmartin@oma.com> writes:

> Of course later on, someone asks us to sieze and release a mutex for each
> iteration of the loop.  We'd like to put the seize as the first line of the
> loop body, and the release as the last line of the loop body.  But if there
> are early exits, then we must put a release before every exit.

No.  Use a controlled type (construction/deconstruction) to
automatically seize and release:

loop
   declare
      Lock : Mutex_Lock (Mutex'Access);
   begin
      <use the resource controlled by Mutex>
   end;
end loop;


When you enter the loop, the Lock object elaborates, and during its
initialization, it automatically calls the Seize operation of Mutex.

When you leave the loop - via a return, or an exit, or an exception, or
whatever - the Lock object is Finalized, during which time it
automatically calls the Release operation of Mutex.

So no, you don't have to worry about bailing out early.  There is no
maintenance penalty for an early return from the loop.