Parallel processing and further use of output

[Meta via Digitalmars-d-learn]

On Saturday, 26 September 2015 at 12:33:45 UTC, anonymous wrote:
>     foreach (f; parallel(iota(1, 1000000+1)))
>     {
>         synchronized i += f;
>     }

Is this valid syntax? I've never seen synchronized used like this 
before.