# GC Bug? Ruby 1.8.4 core dumps on a very small extension
**URL:** https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061
**Category:** ruby-talk
**Created:** [19 February 2006 22:47 UTC](https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061 "2006-02-19T22:47:40Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Danie\_Roux](https://rubytalk.org/u/Danie_Roux)
#### Post date: [19 February 2006 22:47 UTC](https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061/1 "2006-02-19T22:47:40Z")
Hi all,
Long (and tiring) story short:
I have an extension that is 40 lines\* in total, the C code and Ruby
code that exercise it. It core dumps, while I repeatedly call a method
that just returns Qtrue.
All it really does is:
rb\_iv\_set(self, "@v", 100);
in initialize. If I change that 100 to 99, it doesn't core dump.
Change it back to 100, it core dumps within a few seconds.
Further, the while loop that executes it looks like this:
while true
print ''
b.buzz
end
If I take out the print statement, it keeps on running. Put back the
print statement, and it core dumps.
This is a self-compiled 1.8.4 on Ubuntu i386. A friend confirms that
the same thing happens to him on Gentoo with 1.8.4.
I am attaching the code, hopefully its going to come through.
\* It was around 600, and use to core dump every 8 hours or so.
Snipping it down to these 40 lines was pure blind luck, and many 8
hour turnaround iterations.
[funny\_fail.tar.gz](https://rubytalk.org/uploads/short-url/r6YMOK1XXrZe5IS4qeGc3CYDsBi.gz) (540 Bytes)
> **···**
>
> --
> Danie Roux \*shuffle\* Adore Unix [http://blog.acolyte.co.za](http://blog.acolyte.co.za)
---
### Author:  [@Ross\_Bamford4](https://rubytalk.org/u/Ross_Bamford4)
#### Post date: [19 February 2006 23:04 UTC](https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061/2 "2006-02-19T23:04:50Z")
Please try making this change:
--- buzz-orig.c 2006-02-19 23:01:22.000000000 +0000
+++ buzz.c 2006-02-19 23:01:56.000000000 +0000
@@ -8,7 +8,7 @@
static VALUE initialize(VALUE self)
{
- rb\_iv\_set(self, "@v", 100);
+ rb\_iv\_set(self, "@v", INT2FIX(100));
return self;
}
> **···**
>
> On Mon, 2006-02-20 at 07:47 +0900, Danie Roux wrote:
>
> > Hi all,
> >
> > Long (and tiring) story short:
> >
> > I have an extension that is 40 lines\* in total, the C code and Ruby
> > code that exercise it. It core dumps, while I repeatedly call a method
> > that just returns Qtrue.
>
> --
> Ross Bamford - rosco@roscopeco.REMOVE.co.uk
---
### Author:  [@Danie\_Roux](https://rubytalk.org/u/Danie_Roux)
#### Post date: [21 February 2006 16:54 UTC](https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061/3 "2006-02-21T16:54:00Z")
Ross,
Thank you. Moral of the story: Explicitly cast any C value into a Ruby one.
It still strikes me odd that it would run a couple of hundred
iterations before breaking, though.
> **···**
>
> On 2/20/06, Ross Bamford \ wrote:
>
> > On Mon, 2006-02-20 at 07:47 +0900, Danie Roux wrote:
> > \> Hi all,
> > \>
> > \> Long (and tiring) story short:
> > \>
> > \> I have an extension that is 40 lines\* in total, the C code and Ruby
> > \> code that exercise it. It core dumps, while I repeatedly call a method
> > \> that just returns Qtrue.
> >
> > Please try making this change:
> > - rb\_iv\_set(self, "@v", 100);
> > + rb\_iv\_set(self, "@v", INT2FIX(100));
>
> --
> Danie Roux \*shuffle\* Adore Unix [http://blog.acolyte.co.za](http://blog.acolyte.co.za)
---
### Author:  [@Charles\_Mills1](https://rubytalk.org/u/Charles_Mills1)
#### Post date: [21 February 2006 19:33 UTC](https://rubytalk.org/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/25061/4 "2006-02-21T19:33:31Z")
Danie Roux wrote:
> **···**
>
> > On 2/20/06, Ross Bamford \ wrote:
> > \> On Mon, 2006-02-20 at 07:47 +0900, Danie Roux wrote:
> > \> \> Hi all,
> > \> \>
> > \> \> Long (and tiring) story short:
> > \> \>
> > \> \> I have an extension that is 40 lines\* in total, the C code and Ruby
> > \> \> code that exercise it. It core dumps, while I repeatedly call a method
> > \> \> that just returns Qtrue.
> > \>
> > \> Please try making this change:
> > \> - rb\_iv\_set(self, "@v", 100);
> > \> + rb\_iv\_set(self, "@v", INT2FIX(100));
> >
> > Ross,
> >
> > Thank you. Moral of the story: Explicitly cast any C value into a Ruby one.
> >
> > It still strikes me odd that it would run a couple of hundred
> > iterations before breaking, though.
> >
> > --
> > Danie Roux \*shuffle\* Adore Unix [http://blog.acolyte.co.za](http://blog.acolyte.co.za)
>
> Assuming you're using a 32bit machine. 100 % 4 == 0, so Ruby thinks
> 100 is a pointer to a Ruby object. (Dereferencing 100 causes the core
> dump.) 99 % 2 == 1, so 99 looks like a Fixnum to Ruby -- but not 99,
> 99\>\>1 I think.
>
> It may take a couple hundred iterations before the GC runs.
>
> -Charlie