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From: jp@eiffel.UUCP (Jean-Pierre Sarkis)
Newsgroups: comp.lang.eiffel
Subject: Re: Garbage Collection Problem
Summary: Patch for Eiffel 2.2B Garbage Collector
Message-ID: <415@eiffel.UUCP>
Date: 28 Sep 90 21:18:06 GMT
References: <124@alfrat.uucp> <742@tetrauk.UUCP>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 102

In article <124@alfrat.uucp>, dave@alfrat.uucp (Dave Cullen) writes:
>I have been having problems with Segmentation errors being
>created when turning on the automatic garbage collection
>in Eiffel 2.2, using the option in the SDF. I used garbage
>collection in Eiffel 2.1 without any problems, but since
>the occurence of the bug seems to be program size dependent
>this may have been luck.
>
>  [ ... stuff deleted ... ]
>
>(1) - Has anyone seen anything like this happen before?
>(2) - Is it possible that the garbage collector allowed
>      the reuse of some memory that wasn't completely dead, i.e.
>      overwriting part of my STRING object.

 (1): Yes, we did !
 (2): No. But some new features added in 2.2B have forced
 us to rewrite some parts of the Garbage Collector and unfortunately
 introduce bugs in the code.

>This problem is quite urgent so if you've already solved it
>or have any ideas about how to isolate it, I'd be most grateful.
>Thanks

	Included at the end of this articles is a patch to partially fix
	the garbage collector as delivered by ISE in Eiffel 2.2B.

The patch mainly fixes the bug reported by Rick Jones in <742@tetrauk.UUCP>:
>
>  [ ... stuff deleted ... ]
>
>One particular problem which may occur is also due to expanded types, and only
>indirectly involves the garbage collector, despite the fact that that is where
>it crashes!  This problem is quite specific, and occurs if you call the Create
>routine on a class which contains an expanded object, and where any of the
>actual arguments to Create are themselves function calls on other objects.
>
>  [ ... stuff deleted ... ]
>
>This problem does not appear to be resolved in 2.3 (not beta anyway).

	This problem has been fixed in release 2.3, scheduled for
	release the end of October.

	The idea is to prevent the expanded attribute from being marked
	by the GC when the object containing it has not completely initialized.
	For those who report that they are not using any expanded attributes
	in their application; ANY is a client of STD_FILES which is a client
	of FILE. FILE has a DOUBLE attribute and DOUBLE is an expanded type.
	Thus, any Eiffel application using input/output facilities has an
	expanded object at run-time. :-)


*******************************************************************
		PATCH for EIFFEL 2.2B GARBAGE COLLECTOR

1) DO a BACKUP of the directory $INSTALLATION/Eiffel/files

2) Apply the following diffs on the file $INSTALLATION/Eiffel/files/_gac.c
------------------------ DIFF START -----------------------------
diff _gac.c.old _gac.c.patched:
279c279
<                   	(((int32)_rt_3A7 + (int32)c_fd_nb(_rt_3A7) + _rt_40a )
---
>                   	(((int32)_rt_3A7 + _rt_40d*((int32)c_fd_nb(_rt_3A7) + _rt_40a))
300c300
<          n = set_black (_rt_3A7, n);
---
>          if (_rt_3A7->nobj) n = set_black (_rt_3A7, n);
446c446
<                   	(((int32)_rt_3A7 + (int32)c_fd_nb(_rt_3A7) + _rt_40a )
---
>                   	(((int32)_rt_3A7 + _rt_40d*((int32)c_fd_nb(_rt_3A7) + _rt_40a))
467c467
<          _rt_3Al (_rt_3A7);
---
>          if (_rt_3A7->nobj) _rt_3Al (_rt_3A7);
------------------------ DIFF END -----------------------------

3) Save the file and generate the new run_time archive:

(Check the CFLAGS in makefile _makeD:
		`-O -DBSD' or `-O -DSYSTEMV' depending on your Unix system)

   execute:
			make -f _makeD

4) Recompile your application with the GARBAGE COLLECTOR turned ON
*******************************************************************


Hope this will help,


Jean-Pierre SARKIS
jp@eiffel.com
(Technical support: eiffel@eiffel.com)
-- 
Jean-Pierre SARKIS
Interactive Software Engineering

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