Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!hub.ucsb.edu!eiffel!nosmo
From: nosmo@eiffel.UUCP (Vince Kraemer)
Newsgroups: comp.lang.eiffel
Subject: Re: eiffel and external c routines
Summary: previous posting and correction
Message-ID: <421@eiffel.UUCP>
Date: 19 Oct 90 00:21:32 GMT
References: <444@kepler1.kepler.com>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 151

If you have been having trouble with the issue of using Eiffel objects
in C code and have access to a fairly good archive of comp.lang.eiffel,
I would suggest (re)reading message <391@eiffel.UUCP>, which covers the
subject and agrees with the implementation of 2.2 (and 2.3). If you
don't, I can post it again or mail it to you (depending on the demand).

Another item covered in the cited article is the use of class MEMORY to
deal with the disposal of externally allocated resources, when an object
is garbage collected.  Well, I hate to say it, but I believed the
documentation in the class and the semantics that were discussed when
this feature was being designed.  In testing this feature, I discovered
that it works, if you respect the following caveats, which are not
documented: 

1. The dispose will only work in DIRECT descendants of MEMORY only.

2. The dispose feature is only called when the routine MEMORY.full_collect is
   called (not MEMORY.collect is called or when the collection is
   triggered automatically).  This does limit the applicability of 
   using dispose or of automatic memory management considerably.

There is a caveat, for those who can still make good use of
dispose, to apply when writing dispose routines:

   DO NOT apply remote notation (dots) to attributes.  There is no order
   implied in the collection of garbage.  This means that it is possible
   that an attribute of an object has been collected before it client.
   Trying to dereference the collected object will raise an exception.

I wish to apologize to all those who may have been mislead by my
previous posting.  I have learned my leason though: test then post.

The following shar file has a system to illustrate the use of
dispose (correctly).

Vince Kraemer
ISE Tech. Support
(technical correspondence to: eiffel@eiffel.com)

----------------------------- sh-archive -------------------------------

# This is a shell archive.  Remove anything before this line,
# then unpack it by saving it in a file and typing "sh file".
#
# Wrapped by geneve!nosmo on Thu Oct 18 17:12:48 PDT 1990
# Contents:  a.e driver.e .eiffel
 
echo x - a.e
sed 's/^@//' > "a.e" <<'@//E*O*F a.e//'
--|---------------------------------------------------------------
--|   Copyright (C) Interactive Software Engineering, Inc.      --
--|    270 Storke Road, Suite 7 Goleta, California 93117        --
--|                   (805) 685-1006                            --
--| All rights reserved. Duplication or distribution prohibited --
--|---------------------------------------------------------------
--| Author: Vincent Kraemer @ Interactive Software Engineering
--| Created: Thu Oct 18 09:26:43 1990

class A export
	
inherit

	MEMORY redefine dispose;
		
feature

	a1, a2, a3, a4: integer;
	
	dispose is
		do
			-- The use of io will be okay since it is shared.
			-- all others you must be careful about.
			io.putstring ("Disposing of an A.");
			io.new_line;
		end;

end -- class A
@//E*O*F a.e//
chmod u=rw,g=rw,o=r a.e
 
echo x - driver.e
sed 's/^@//' > "driver.e" <<'@//E*O*F driver.e//'
class DRIVER export
	
inherit

	MEMORY
	
feature
	
	hold: ARRAY [A];

	Create is
		local
			an_a: A;
			ol, il: integer;
		do
			io.putstring ("Now using manual storage control.");
			io.new_line;
			collection_off;
			from
				ol := 0
			until
				ol = 200
			loop
				io.putstring ("second test: ");
				io.putint (ol);
				io.new_line;
				hold.create (0, 100000);
				from il := 0;
				until il > 100000
				loop
					an_a.create;
					hold.put (an_a, il);
					il := il + 1;
				end;
				ol := ol + 1;
				hold.forget;
				full_collect;
				collection_off;
			end;
		end;
			
end -- class DRIVER
@//E*O*F driver.e//
chmod u=rw,g=rw,o=r driver.e
 
echo x - .eiffel
sed 's/^@//' > ".eiffel" <<'@//E*O*F .eiffel//'
------------ EIFFEL SYSTEM DESCRIPTION FILE -------------------
--   For simple uses, just replace ``root_class_name'' below
--   by the name of the root class of your system (lower case)
ROOT: driver
UNIVERSE: /usr/local/Eiffel/library/support
EXTERNAL:
NO_ASSERTION_CHECK (N):
PRECONDITIONS (Y): ALL
ALL_ASSERTIONS (N):
DEBUG (N):
TRACE (N):
OPTIMIZE (N):
GARBAGE_COLLECTION (y)
C_PACKAGE (N):
C_EXTERNAL:
MAKE:
VISIBLE (N):
----------------------------------------------------------------
@//E*O*F .eiffel//
chmod u=rw,g=rw,o=r .eiffel
 
exit 0