Difference between __gshared and shared.

[deadalnix via Digitalmars-d]

On Thursday, 9 July 2015 at 14:57:56 UTC, Márcio Martins wrote:
> On Thursday, 9 July 2015 at 14:03:18 UTC, Jonathan M Davis 
> wrote:
>> On Thursday, 9 July 2015 at 12:39:00 UTC, Márcio Martins wrote:
>>>[...]
>> Well, the compiler is free to assume that a variable that is 
>> not marked as shared is thread-local. So, it's free to make 
>> optimizations based on that. So, for instance, it can know for 
>> a fact that
>>
>> [...]
>
> But this is what a C/C++ compiler would do, unless you your 
> data is qualified as volatile. I believe __gshared also implies 
> the volatile behavior, right? I wouldn't make sense any other 
> way.
>
> So basically, __gshared is like saying "I want the C/C++ 
> behavior, and I accept I am all on my own as the compiler will 
> not help me".

If you think volatile is going to help you with concurency, you 
gonna have bad time.

The only thing volatile does is to prevent register promotion of 
the variable. It is usefull for MMIO, it doesn't provide 
guarantee for multithreading.