Determination of thread status.

[Vitaly]

> std.concurrency is a low-level API. You may be looking for a 
> higher level API: std.parallelism. See Task.done(), 
> https://dlang.org/phobos/std_parallelism.html#.Task.done
>
> Bastiaan.
Maybe I misunderstood, but the capabilities of the 
std.parallelism module do not allow to exchange messages with the 
stream, if so, this does not suit me.
Correct me if it is not.