VisualD: Error disabling access to shared memory objects

[Nuno Leiria]

If I enable "disable access to shared memory objects (DMD 
2.088+)" then this simple example doesn't compile:

void main()
{
     string line;
     while ((line = stdin.readln()) !is null)
         write(line);
}

It fails with the error:

C:\D\dmd-2.094.0\windows\bin\..\..\src\phobos\std\stdio.d-mixin-4874(4874): Error: direct access to shared `stdin` is not allowed, see `core.atomic`

Can anyone explain why?