On 10/20/2011 11:13 AM, mark florisson wrote:
On 20 October 2011 09:42, Dag Sverre Seljebotn
<d.s.seljeb...@astro.uio.no> wrote:
Meta: I've been meaning to respond to this thread, but can't find the time.
What's the time-frame for implementing this? If it's hypothetical at the
moment and just is a question of getting things spec-ed, one could perhaps
look at discussing it at the next Cython workshop, or perhaps a Skype call
with the three of us as some point...
For me this is just about getting this spec-ed, so that when someone
finds the time, we don't need to discuss it for weeks first. And the
implementor won't necessarily have to support everything at once, e.g.
just critical sections or barriers alone would be nice.
Is there any plan for a new workshop then? Because if it's in two
years I think we could be more time-efficient :)
At least in William's grant there's plans for 2-3 Cython workshops, so
hopefully there's funding for one next year if we want to. We should ask
him before planning anything though.
Regarding the tasks: One of my biggest problems with Python is the lack of
an elegant syntax for anonymous functions. But since Python has that
problem, I feel it is not necesarrily something we should fix (by using the
with statements to create tasks). Sometimes Pythonic-ness is more important
than elegance (for Cython).
I agree it's not something we should fix, I just think tasks are most
useful in inline blocks and not in separate functions or closures.
Although it could certainly work, I think it restricts more, leads to
more verbose code and possibly questionable semantics, and on top of
that it would be a pain to implement (although that should not be used
as a persuasive argument). I'm not saying there is no elegant way
other than with blocks, I'm just saying that I think closures are not
the right thing for it.
In general I'm happy as long as there's a chance of getting things to work
in pure Python mode as well (with serial execution). So if, e.g., with
statements creating tasks have the same effect when running the same code
(serially) in pure Python, I'm less opposed (didn't look at it in detail).
Yes, it would have the same effect. The thing with tasks (and OpenMP
constructs in general) is that usually if your compiler ignores all
your pragmas, your code just runs serially in the same way. The same
would be true for the tasks in with blocks.
Short note: I like the vision of Konrad Hinsen:
http://www.euroscipy.org/talk/2011
The core idea is that the "task-ness" of a block of code is orthogonal
to the place you actually write it. That is, a block of code may often
either be fit for execution as a task, or not, depending on how heavy it
is (= values of arguments it takes in, not its contents).
He introduces the "async" expression to drive this point through.
I think "with task" is fine if used in this way, if you simply call a
function (which itself doesn't know whether it is a task or not). But
once you start to implement an entire function within the with-statement
there's a code-smell.
Anyway, it's growing on me. But I think his "async" expression is more
Pythonic in the way that it forces you away from making your code smell.
We could simply have
async(func)(arg, arg2, somekwarg=4)
(He also says "functional-style programming is better for parallization
than threads+locks", which I can kind of agree with but nobody tried to
make an efficient immutable array implementation suitable for numerical
computation yet to my knowledge... that's an interesting MSc or
PhD-topic, but I already have one :-) )
(Look at me, going along discussing when I really shouldn't -- see you
later.)
Dag Sverre
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