Re: [Boost-users] [thread] variables in thread examples require 'volatile'?

Subject: Re: [Boost-users] [thread] variables in thread examples require 'volatile'?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-12-07 19:56:21

AMDG

Gabriel Redner wrote:
> I'm involved in a bit of a dispute in which a colleague is claiming
> that 'volatile' is necessary to make certain synchronization patterns
> correct.  As part of my response I pointed out that the boost.thread
> examples don't use it, but he maintains his position - saying that the
> examples are flawed.  I'm frankly somewhat out of my element here, and
> I'd like to get input from people who have presumably thought about
> this stuff a good deal.
>
> The example in question is here, under "synopsis":
> http://www.boost.org/doc/libs/1_41_0/doc/html/thread/synchronization.html#thread.synchronization.condvar_ref
>
> The claim is that 'volatile' is needed on the boolean, otherwise the
> compiler might cache the boolean in a register, and the loop would
> never exit.  He cites for support two articles:
>
> http://www.ddj.com/cpp/184403766
> https://www.securecoding.cert.org/confluence/display/seccode/DCL17-C.+Beware+of+miscompiled+volatile-qualified+variables
>
> Who's right?
>   

volatile is not needed in that example because access is protected by a 
mutex.

In Christ,
Steven Watanabe