From: nobu.nokada@...
Date: 2003-10-08T23:29:07+09:00
Subject: Re: GC and the stack

Hi,

At Wed, 8 Oct 2003 23:09:08 +0900,
Thomas Sondergaard wrote:
> I have heard statements indicating that you need to declare all local VALUEs
> volatile, in order to ensure that they are put on the stack by the compiler
> and not in a register. Can I get an authoritative answer to this question?
> The ruby source code is full of "volatile", but it is not mentioned once
> either on the rubygarden.org WIKI or the README.EXT. Why should this be
> necessary? Couldn't the garbage collector check the registers too?

Unnecessary, in general.  GC checks the registers of course.

However, you have to pay attention in this situation.

  VALUE str = rb_str_new(0, 256); /* make a buffer */
  char *ptr = RSTRING(str)->ptr;

If str isn't used later, compiler may remove it.  And then ptr
may be freed when you call ruby APIs and GC runs.
StringValue() and StringValuePtr() are provided to avoid this.

-- 
Nobu Nakada