[Cython] prange CEP updated

Robert Bradshaw robertwb at math.washington.edu
Thu Apr 21 10:37:29 CEST 2011

On Mon, Apr 18, 2011 at 7:51 AM, mark florisson
<markflorisson88 at gmail.com> wrote:
> On 18 April 2011 16:41, Dag Sverre Seljebotn <d.s.seljebotn at astro.uio.no> wrote:
>> Excellent! Sounds great! (as I won't have my laptop for some days I can't
>> have a look yet but I will later)
>> You're right about (the current) buffers and the gil. A testcase explicitly
>> for them would be good.
>> Firstprivate etc: i think it'd be nice myself, but it is probably better to
>> take a break from it at this point so that we can think more about that and
>> not do anything rash; perhaps open up a specific thread on them and ask for
>> more general input. Perhaps you want to take a break or task-switch to
>> something else (fused types?) until I can get around to review and merge
>> what you have so far? You'll know best what works for you though. If you
>> decide to implement explicit threadprivate variables because you've got the
>> flow I certainly wom't object myself.
>  Ok, cool, I'll move on :) I already included a test with a prange and
> a numpy buffer with indexing.

Wow, you're just plowing away at this. Very cool.

+1 to disallowing nested prange, that seems to get really messy with
little benefit.

In terms of the CEP, I'm still unconvinced that firstprivate is not
safe to infer, but lets leave the initial values undefined rather than
specifying them to be NaNs (we can do that as an implementation if you
want), which will give us flexibility to change later once we've had a
chance to play around with it.

The "cdef threadlocal(int) foo" declaration syntax feels odd to me...
We also probably want some way of explicitly marking a variable as
shared and still be able to assign to/flush/sync it. Perhaps the
parallel context could be used for these declarations, i.e.

    with parallel(threadlocal=a, shared=(b,c)):

which would be considered an "expert" usecase.

For all the discussion of threadsavailable/threadid, the most common
usecase I see is for allocating a large shared buffer and partitioning
it. This seems better handled by allocating separate thread-local
buffers, no? I still like the context idea, but everything in a
parallel block before and after the loop(s) also seems like a natural
place to put any setup/teardown code (though the context has the
advantage that __exit__ is always called, even if exceptions are
raised, which makes cleanup a lot easier to handle).

- Robert

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