Path: utzoo!attcan!uunet!mcsun!unido!alfrat!alfrat.uucp!dave
From: dave@alfrat.uucp (Dave Cullen)
Newsgroups: comp.lang.eiffel
Subject: Garbage Collection Problem
Message-ID: <124@alfrat.uucp>
Date: 26 Sep 90 18:50:47 GMT
Sender: dave@alfrat.uucp
Reply-To: dave@alfrat.uucp (Dave Cullen)
Organization: A+F System-Entwicklung, W-Germany
Lines: 43

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.

So far I have traced the segmentation error to the function
"set_black" in "_gac.c". It occurs on the second of the following
two lines:

	_rt_3A7 = c_field ((int32)i, _rt_3Ao);
	if (!EXPANDED(_rt_3A7)) {
	...

The object pointed at by "_rt_3Ao" is a STRING and in memory looks
as follows:

	0xc0000002
	0x41f49c
	0xc1000035
	0x41f220

After the call to "c_field", "_rt_3A7" is set to 0xc1000035. Whilst
this should theoretically be an object pointer to the area of memory
used for the actual string, it looks rather more like the "info"
part of an object. In my system this looks like the start of a
LINKED_LIST object.

Questions:
(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.

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,

Dave Cullen            | Tel. 02102-850514
A&F System Entwicklung | Email: dave@alfrat.uucp
4030 Ratingen          | Maybe: ...!unido!alfrat.uucp!dave
W. Germany             | Meine Beutelmaus hat verstopfung!