Re: volatile and 2 processor

Bruno Causse wrote:
> hi all
> 
> the key word "volatile" have a sence on dual processor?
> 
> (not dual core, real dual processor ex : 2*xeon)

"volatile" has a number of specifically defined behaviours (useful when 
accessing hardware registers, or variables that may have been modified 
in a signal handler, or when playing with setjmp/longjmp).

It's often misused for concurrent programming--just check how many times 
Dave Butenhof has tried to explain to people why it's not suitable for 
lockless algorithms.

If you use regular locks to protect data access, then the "volatile" 
keyword is not necessary because the locks ensure visibility and 
ordering "behind the scenes".

If you use lockless access patterns with appropriate compiler and 
hardware read/write barriers, then the "volatile" keyword is not
necessary.

So basically, outside of the specific areas described above, "volatile" 
is both unnecessary and insufficient.

Chris