Parallel processing and further use of output

[John Colvin via Digitalmars-d-learn]

On Saturday, 26 September 2015 at 12:18:16 UTC, Zoidberg wrote:
> I've run into an issue, which I guess could be resolved easily, 
> if I knew how...
>
> [CODE]
>     ulong i = 0;
>     foreach (f; parallel(iota(1, 1000000+1)))
>     {
>         i += f;
>     }
>     thread_joinAll();
>     i.writeln;
> [/CODE]
>
> It's basically an example which adds all the numbers from 1 to 
> 1000000 and should therefore give 500000500000. Running the 
> above code gives 205579930677, leaving out "thread_joinAll()" 
> the output is 210161213519.
>
> I suspect there's some sort of data race. Any hint how to get 
> this straight?

Here's a correct version:

import std.parallelism, std.range, std.stdio, core.atomic;
void main()
{
     shared ulong i = 0;
     foreach (f; parallel(iota(1, 1000000+1)))
     {
         i.atomicOp!"+="(f);
     }
     i.writeln;
}