[phobos] Parallelism in Phobos

[David Simcha]

  Filed, now that I understand shared a little better and you reminded 
me about this.

On 9/5/2010 3:08 AM, Andrei Alexandrescu wrote:
> I think both are wrong for different reasons. Did you file them to 
> Bugzilla already?
>
> Andrei
>
> On 07/31/2010 11:45 PM, David Simcha wrote:
>> Also, the following doesn't compile:
>>
>> class Foo {
>>
>>      shared void bar() {}
>> }
>>
>> void main() {
>>      shared(void delegate()) d;
>>      auto foo = new Foo;
>>      d = &foo.bar;
>> }
>>
>> Error: cannot implicitly convert expression (&foo.bar) of type void
>> delegate() to shared(void delegate())
>>
>> But the following does:
>>
>> class Foo {
>>
>>      void bar() {}
>> }
>>
>> void main() {
>>      shared(void delegate()) d;
>>      auto foo = new Foo;
>>      d = &foo.bar;
>> }
>>
>> If these are just plain bugs, let me know and I'll file them in
>> Bugzilla, but right now I feel like they're more likely my lack of
>> understanding of shared.
>>
>>
>> On 7/31/2010 7:31 AM, Andrei Alexandrescu wrote:
>>> 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 <dsimcha at gmail.com
>>> <mailto:dsimcha at gmail.com>> 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://cis.jhu.edu/%7Edsimcha/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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>>>
>>>
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>>
>>
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