[mpiwg-rma] Inconsistency of MPI_WIN_FENCE semantic

[Balaji, Pavan]

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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