Re: [LAU] Simple, easy multithreaded circular buffer library for Linux?

On Fri, Oct 17, 2008 at 02:33:00PM -0400, Paul Coccoli wrote:

> There's no chance that a compiler optimization is hiding the bug,
> because we haven't turned on optimization.

But there is nothing that stops the compiler from writing
read_ptr any number of times it wants unless you make that
variable volatile.

> HOWEVER, if you go back
> to the original version and REMOVE the volatile qualifiers, then
> re-compile with -O2, NOW a compiler optimization is hiding the bug
> (and the test passes)! The rb->read_ptr is presumably cached in a
> register and hence only modified once (giving the same affect as the
> patch).

Indeed. The original version really invited the problem,
by *forcing* the compiler to write read_ptr twice.

Ciao,

-- 
FA
Laboratorio di Acustica ed Elettroacustica
Parma, Italia
Lascia la spina, cogli la rosa.
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