Re: Optimization of conditional access to globals: thread-unsafe?

[Erik Trulsson <ertr1013@student.uu.se>]

On Sun, Oct 28, 2007 at 03:03:46PM -0000, Dave Korn wrote:
> On 28 October 2007 13:32, Bart Van Assche wrote:
> 
> >  Requiring that all
> > thread-shared variables should be declared volatile is completely
> > unacceptable. 
> 
>   Any variable that may be altered by an external unpredictable asynchronous
> 'force majeure' must be declared volatile or the behaviour is undefined.  Your
> code is simply incorrect, and you appear to be demanding that the language
> standards and the compiler all be revised to make the buggy code valid.


Unfortunately it seems that the POSIX standard for threads say that as long
as access to a shared variable is protected by a mutex there is no need to
use 'volatile'.

This means that POSIX essentially defines certain behaviours that the C
standard left undefined.

Personally I think the POSIX standard is broken in this regard, but if
programs that are valid according to POSIX are to work correctly then it is
not sufficient for the compiler to follow the C standard.  It must also not
break any of the guarantees that POSIX makes.


> 
> > We need a solution today for the combination of C/C++
> > and POSIX threads, we can't wait for the respective language
> > standardization committees to come up with a solution.
> 
>   You already have it, but you have declared it "unacceptable" and refused to
> use it without stating any clear reason.
> 
>     cheers,
>       DaveK
> -- 
> Can't think of a witty .sigline today....
> 

-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se