Hello,
Here's a belated answer to your question (hectic times prevented me
from tending to non-urgent email).
I think a parallel library would be great to have as indeed phobos is
geared at general concurrency. Such a lib would also expose bugs and
weaknesses in our model and its implementation.
Andrei
Sent by shouting through my showerhead.
On May 30, 2010, at 12:54 PM, David Simcha <[email protected]> wrote:
I have a few questions/comments about the possible inclusion of a
library for parallelism in Phobos:
1. What is the status of std.concurrency? It's in the source tree,
but it's not in the documentation or the changelogs. It appears to
have been checked in quietly ~3 months ago, and I just noticed now.
2. From reading the description of std.concurrency in TDPL it
seemed more geared toward concurrency (i.e. making stuff appear to
be happening simultaneously, useful for things like GUIs and
servers) rather than parallelism (i.e. the use of multiple CPU cores
to increase throughput, useful for things like scientific computing
and video encoding). It seems fairly difficult (though I haven't
tried yet) to write code that's designed for pull-out-all-stops
maximal performance on a multicore machine, especially since
immutability is somewhat of a straight jacket. I find implicit
sharing and the use of small synchronized blocks or atomic ops to be
very useful in writing parallel programs.
3. Most code where parallelism, as opposed to concurrency, is the
goal (at least most that I write) is parallelized in one or two
small, performance critical sections, and the rest is written
serially. Therefore, it's easy to reason about things and safety
isn't as important as the case of concurrency-oriented
multithreading over large sections of code.
4. I've been eating my own dogfood for awhile on my ParallelFuture
library. (http://cis.jhu.edu/~dsimcha/parallelFuture.html; http://dsource.org/projects/scrapple/browser/trunk/parallelFuture/parallelFuture.d
) It's geared toward throughput-oriented parallelism on multicore
machines, not concurrency for GUIs, servers, etc. and is higher
level than std.concurrency. Is there any interest in including
something like this in Phobos? If so, would we try to make it fit
into the explicit-sharing-only model, or treat it as an alternative
method of multithreading geared towards pull-out-all-stops
parallelism on multicore computers?
One last note: Walter claimed a while back on the NG that
Parallelfuture doesn't compile. I use it regularly and it compiles
for me. Walter, can you please point out what the issue was?
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