David Simcha's std.parallelism

[dsimcha]

Ok, I finally got around to tackling most of this.  See individual 
replies below.

On 1/1/2011 6:07 PM, Andrei Alexandrescu wrote:
> I think David Simcha's library is close to reviewable form. Code:
>
> http://dsource.org/projects/scrapple/browser/trunk/parallelFuture/std_parallelism.d
>
>
> Documentation:
>
> http://cis.jhu.edu/~dsimcha/d/phobos/std_parallelism.html
>
> Here are a few comments:
>
> * parallel is templated on range, but not on operation. Does this affect
> speed for brief operations (such as the one given in the example,
> squares[i] = i * i)? I wonder if using an alias wouldn't be more
> appropriate. Some performance numbers would be very useful in any case.

As I've said before, I strongly believe it's not worth it to give up the 
features (ref iteration, index variables, consistency with non-parallel 
syntax) that opApply offers, given that we also have map() and the 
performance hit is only a small constant that only matters for very 
fine-grained parallelism.  (I've shown it to be pretty small in absolute 
terms with benchmarks.  See previous posts.)

>
> * Why is ThreadPool a class and what are the prospects of overriding its
> members?
>

Made it final.  Done.

> * Can't we define the behavior of break inside a parallel loop?

Done.  It now aborts the current work unit.  A goto from inside the loop 
to outside the loop is still undefined, though, because it makes even 
less sense and raises the possibility of conflicting gotos from 
different threads.

>
> * I think it does make sense to evaluate a parallel map lazily by using
> a finite buffer. Generally map looks the most promising so it may be
> worth investing some more work in it to make it "smart lazy".

I have added LazyMap, which rotates two buffers of a user-specified size 
and computes the map functions and dumps them to the back buffer while 
making the front buffer available via front() and popFront().  One can 
also achieve pipelining by chaining LazyMap objects.

>
> * waitStop() -> join()?

Done.

>
> * The documentation should use more examples. Currently it uses entities
> without defining them (Task, TaskPool etc.)

Can you elaborate on this?  I am having trouble thinking of things to 
add to the docs.
>
> * why runCallable()? There's no runUncallable().

I made this into run().

>
> * Should there be a makeAngel to undo makeDaemon?

Done.  Added makeAngel.