[mpiwg-rma] Inconsistency of MPI_WIN_FENCE semantic

[Balaji, Pavan]

Besides, the second sentence says, if MPI_MODE_NOPRECEDE is given, it’ll not act as a barrier.

What’s the necessity for that if WIN_FENCE does not act as a barrier even when MPI_MODE_NOPRECEDE is not given.

  — Pavan

On Feb 25, 2014, at 9:38 PM, Balaji, Pavan <balaji at anl.gov> wrote:

> 
> 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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