# GC Bug? Ruby 1.8.4 core dumps on a very small extension **URL:** \ **Category:** Ruby\ **Created:** [February 19, 2006, 11:48pm UTC](https://www.ruby-forum.com/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/54001 "2006-02-19T23:48:18Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Danie\_Roux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8c91f0/32.png) [@Danie\_Roux](https://www.ruby-forum.com/u/Danie_Roux)\ **Post date:** [February 19, 2006, 11:48pm UTC](https://www.ruby-forum.com/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/54001/1 "2006-02-19T23:48:18Z")
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. ---
**Author:** ![Danie\_Roux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8c91f0/32.png) [@Danie\_Roux](https://www.ruby-forum.com/u/Danie_Roux)\ **Post date:** [February 20, 2006, 12:06am UTC](https://www.ruby-forum.com/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/54001/2 "2006-02-20T00:06:24Z")
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: — 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)); ---
**Author:** ![Danie\_Roux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8c91f0/32.png) [@Danie\_Roux](https://www.ruby-forum.com/u/Danie_Roux)\ **Post date:** [February 21, 2006, 5:56pm UTC](https://www.ruby-forum.com/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/54001/3 "2006-02-21T17:56:04Z")
On 2/20/06, Ross B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > - 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. ---
**Author:** ![Danie\_Roux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8c91f0/32.png) [@Danie\_Roux](https://www.ruby-forum.com/u/Danie_Roux)\ **Post date:** [February 21, 2006, 8:35pm UTC](https://www.ruby-forum.com/t/gc-bug-ruby-1-8-4-core-dumps-on-a-very-small-extension/54001/4 "2006-02-21T20:35:34Z")
Danie Roux wrote: > > Please try making this change: > > – > > 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