[mpiwg-rma] MPI_Lock... for MPI shared memory

[Jeff Hammond]

This is a bug in the text that should be fixed by an erratum. 

Jeff 

Sent from my iPhone

> On Sep 13, 2016, at 5:36 AM, Rolf Rabenseifner <rabenseifner at hlrs.de> wrote:
> 
> Hello,
> 
> my colleague Joseph detected that an MPI implementation is allowed 
> to not allow passive target communication/synchronization (i.e.,
> all forms of MPI_Lock and Unlock) on MPI shared memory windows.
> 
> Was it intented or is it only a historical review-bug that 
> MPI_WIN_ALLOCATE_SHARED was never added to the list of 
> MPI_ALLOC_MEM (since MPI-2.0), and MPI_WIN_ALLOCATE & 
> MPI_WIN_ATTACH (since MPI-3.0) in the following text.
> 
> 
> MPI-3.1 Sect. 11.5.3 on page 448 lines 1-12 say
> 
> "Implementors may restrict the use of RMA communication 
> that is synchronized by lock calls to windows in 
> memory allocated by MPI_ALLOC_MEM (Section 8.2),
> MPI_WIN_ALLOCATE (Section 11.2.2), or attached with 
> MPI_WIN_ATTACH (Section 11.2.4). 
> Locks can be used portably only in such memory.
> 
> Rationale. The implementation of passive target 
> communication when Memory is not shared may require 
> an asynchronous software agent. Such an agent can be
> implemented more easily, and can achieve better 
> performance, if restricted to specially allocated memory. 
> It can be avoided altogether if shared memory is used. 
> It seems natural to impose restrictions that allows 
> one to use shared memory for third party communication 
> in shared memory machines.
> (End of rationale.)"
> 
> 
> The rationale not really fits to the current state
> that MPI_WIN_ALLOCATE_SHARED is missing in the list. 
> It would fit if MPI_WIN_ALLOCATE_SHARED would be added
> to the list.
> 
> Best regards
> Rolf
> 
> -- 
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
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