From: Paul Brannan <pbrannan@...>
Date: 2007-12-27T05:32:58+09:00
Subject: Re: [Spam] What does volatile assignment of *pos in rb_thread_s_new() do?

On Sun, Dec 16, 2007 at 06:02:16AM +0900, Gonzalo Garramu?o wrote:
> Brent Roman wrote:
> >    volatile VALUE *pos; 
> >
> >    pos = th->stk_pos;  //<--- what does this accomplish?
> 
> It keeps the value in the stack, preventing it from being GC'ed during 
> the run of that (and children) functions.
> 
> The use of volatile is a hint to the compiler to not optimize away the 
> variable.

Wouldn't the same thing be accomplished by marking the member in
thread_mark instead?

I see the same idiom being used in YARV, but I'm skeptical whether it is
used correctly.  IMO any time volatile is used without a comment is a
bug.

One example (vm.c):

    volatile int stored_safe = th->safe_level;

It's unclear even from studying the code in detail why this variable is
marked volatile.

Paul