[Mpi3-rma] [EXTERNAL] Re: request-based ops

[Jim Dinan]

It seems like there are two possible semantics for which operations are
complete by a call to MPI_Win_iflush:

(1) Completes all operations issued by the origin process on the given
window before MPI_Win_iflush was called.
(2) Completes all operations issued by the origin process on the given
window before MPI_Win_iflush completed.

So far, we've just been looking at #1, but I think that #2 is worth
considering.  Option #2 allows an implementation that just checks if the
counters are equal.  This avoids the issue where #1 can't be implemented in
terms of #2, because issuing an unbounded number of operations while
testing on the iflush request can cause the iflush to not complete
indefinitely.

Option #2 does not directly provide the functionality that Jeff was looking
for, but this could be implemented using two windows.  Issue a bunch of
operations on win1 and iflush on win2, when win2 has been flushed, switch
to issuing operations on win2 and iflushing win1.

 ~Jim.

On Mon, Jun 17, 2013 at 7:38 AM, Jim Dinan <james.dinan at gmail.com> wrote:

> Sorry, I should have been more specific.  An implementation of iflush that
> waits for the completion of all messages should be valid.  Such an
> implementation would compare counters and return true if they are the
> same.  This implementation could have the issue I mentioned in the previous
> message, where the user continuously issuing operations can prevent iflush
> from completing.
>
> Jim.
> On Jun 16, 2013 10:13 AM, "Pavan Balaji" <balaji at mcs.anl.gov> wrote:
>
>>
>> On 06/16/2013 10:02 AM, Jim Dinan wrote:
>>
>>> If the channel is unordered, a message after the iflush can increment
>>> the counter, while one before the iflush has not yet completed.  So, the
>>> counter is not enough to mark a particular point in time.
>>>
>>
>> Ah, good point.
>>
>>  An implementation of iflush as flush should still be valid, right?  Just
>>>
>>
>> No.  You cannot do this if the user only uses TEST.
>>
>> MPI_WIN_IFLUSH(&req);
>> while (MPI_TEST(req) is not done);
>>
>>  -- Pavan
>>
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
>>
>
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