[mpiwg-rma] Inconsistency of MPI_WIN_FENCE semantic

[Zhao, Xin]

I agree with this. If the handshake is done in the first RMA operation after the fence, then that operation becomes blocking. In Standard P418 it says all communication calls are non-blocking. 

Xin
________________________________________
From: mpiwg-rma [mpiwg-rma-bounces at lists.mpi-forum.org] on behalf of Balaji, Pavan [balaji at anl.gov]
Sent: Tuesday, February 25, 2014 9:38 PM
To: MPI WG Remote Memory Access working group
Subject: Re: [mpiwg-rma] Inconsistency of MPI_WIN_FENCE semantic

In practice, it’ll need to have barrier semantics.  Otherwise, PUT will need to be a two-sided operation to ensure that it’s not issued before the other process calls MPI_WIN_FENCE.

  — Pavan

On Feb 25, 2014, at 9:21 PM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:

>> (1) On P440-P441 it say that "RMA operations on win started by a process after the fence call returns will access their target window only after MPI_WIN_FENCE has been called by the target process". This requires MPI_WIN_FENCE that starts an epoch to act as an barrier.
>
> It only says "RMA operations on win started by a process after the fence call returns will access their target window only after MPI_WIN_FENCE has been called by the target process".   NOT   "This requires MPI_WIN_FENCE that starts an epoch to act as an barrier."
>
> Why does the fence have to act as a barrier. The handshake could be done when first RMA operation is called after the fence.
>
> Rajeev
>
>
> On Feb 25, 2014, at 8:41 PM, "Zhao, Xin" <xinzhao3 at illinois.edu> wrote:
>
>> Hi all,
>>
>> There is an inconsistency of MPI_WIN_FENCE semantic in MPI 3.0 Standard that makes me confused:
>>
>> (1) On P440-P441 it say that "RMA operations on win started by a process after the fence call returns will access their target window only after MPI_WIN_FENCE has been called by the target process". This requires MPI_WIN_FENCE that starts an epoch to act as an barrier.
>>
>> (2) However, (1) contradict with the word at end of P441: "a call to MPI_WIN_FENCE that is known not to end any epoch (in particular a call with assert equal to MPI_MODE_NOPRECEDE) does not necessarily act as a barrier".
>>
>> Should the word of (1) add: "when MPI_MODE_NOPRECEDE is not given"?
>>
>> Thanks,
>>
>> Xin
>>
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