From: Robert Buck <lists@...>
Date: 2012-11-24T22:44:28+09:00
Subject: C Extension: Why would VALUE state appear differently during shutdown than immediately before it?

I have a graph of objects in a C extension, and as such I maintain
reference counts from children to parents as deallocations are order
dependent (see struct definition below).

While I run my program the reference counts match up, but when the
program exits, when ruby dumps its entire object table calling free on
every VALUE the parent's free functions are called before the children
as the parents were allocated first and they appear in the ruby object
table first (this was the whole reason for adding reference counting,
because otherwise order dependent deallocations in C code causes a
SEGV).

Anyways, before shutdown here are my ref counts:

[REFERENCE COUNT][O INCR] (child @ 00007fd6d0ddd5c0): 1 (parent @
00007fd6d2538460): 2

n.b. 2 refs

And after shutdown the ref counts are "magically" different:

[REFERENCE COUNT][I DECR] (child @ 00007fd6d2538460): 1 (parent @
0000000000000000): -10

n.b. -10 is just a sentinel marker, ignore that
n.b. 1 refs though does not match 2 above

The latter trace is for the root object, hence no parent. But notice the
root object's reference count of 1. Take a look at its reference count
before program termination, 2.

This is saying that I have a case of memory corruption on my part,
memory corruption on ruby's part, or my understanding of how to set up
graphs of interrelated objects in C extensions is seriously flawed.

Regarding the last option, all I am doing is maintaining a struct of:

struct handle
{
    RUBY_DATA_FUNC free_func;
    rb_atomic_t atomic;
    VALUE parent;
};

Would someone have an idea of how to approach this, what could possibly
be going on? I have been at this for three days now and I don't see any
bug on my part.

Bob

-- 
Posted via http://www.ruby-forum.com/.