std.parallelism: How to wait all tasks finished?

[Cooler]

On Thursday, 6 February 2014 at 17:58:47 UTC, Russel Winder wrote:
> On Mon, 2014-02-03 at 00:00 +0000, Cooler wrote:
>> I have several tasks. Each task may or may not create another 
>> task. What is the best way to wait until all tasks finished?
>
> What you are describing here is a classic fork/join 
> architecture. The
> tasks are structured as a tree with synchronization handled by 
> the
> sub-nodes.
>
> As far as I am aware std.parallelism focuses on data 
> parallelism which
> is a scatter/gather (aka map/reduce) model of just a single 
> layer.
>
> All the code fragments in the thread have, I believe, been 
> predicated on
> working with a thread pool as an explicit global entity. I 
> think the
> problems have stemmed from taking this viewpoint.
>
> I would suggest following the way the Java fork/join framework 
> (based on
> Doug Lea's original) works. There is an underlying global 
> thread pool,
> but the user code uses the fork/join abstraction layer in order 
> to
> create the tree of synchronization dependencies. In this case 
> instead of
> working with tasks directly there needs to be a type whose job 
> it is to
> be a non-leaf node in the tree that handles synchronization 
> whilst
> nonetheless creating tasks and submitting them to the pool.
>
> This is clearly something that could turn into an addition to
> std.parallelism or be std.forkjoin.
>
> Sorry I have no actual code to offer, but the overall design of 
> what is
> needed is well understood, at least in the Java context. C++ 
> has a long
> way to go to catch up, as does D.
>
> The other thing that then sits on this is lazy stream 
> parallelism, which
> is what Java 8 is adding to the mix.

Thank you for your verbose answer. I think the solution could be 
shorter and simpler :)