[mpiwg-rma] Ticket #456 - synchronization in MPI-3.0's shared memory

[Rolf Rabenseifner]

Dear Keith,

> Apparently, C11 solves all of these issues (or, at least, that is
> what I have been led to believe), and modern C compilers honor the
> C11 memory model.

Thank you for giving me this second approval.
Bill's answer is already on 
https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/456#comment:13

Best regards
Rolf

----- Original Message -----
> From: "Keith D Underwood" <keith.d.underwood at intel.com>
> To: "Rolf Rabenseifner" <rabenseifner at hlrs.de>
> Sent: Wednesday, October 1, 2014 5:40:14 AM
> Subject: RE: Ticket #456 - synchronization in MPI-3.0's shared memory
> 
> Apparently, C11 solves all of these issues (or, at least, that is
> what I have been led to believe), and modern C compilers honor the
> C11 memory model.
> 
> > -----Original Message-----
> > From: Rolf Rabenseifner [mailto:rabenseifner at hlrs.de]
> > Sent: Thursday, September 11, 2014 3:13 AM
> > To: Underwood, Keith D
> > Cc: Bill Long
> > Subject: Fwd: Ticket #456 - synchronization in MPI-3.0's shared
> > memory
> > 
> > Dear Keith,
> > 
> > welcome back from your sabbatical. I hope you had nice weeks.
> > 
> > I sent Bill Long the following question (see below) and I would
> > have the same
> > question about the Intel Compilers (C, C++ and Fortran).
> > 
> > This question is independent of the details of a threading library
> > and whether
> > OS threads or processes are used.
> > 
> > Therefore any answer about pthreads would also fit to #456, i.e.,
> > the
> > synchronization in the errata about MPI-3.0 shared memory.
> > 
> > It would be nice, if you can get the answers to the questions
> > below.
> > 
> > Best regards
> > Rolf
> > 
> > ----- Forwarded Message -----
> > From: "Rolf Rabenseifner" <rabenseifner at hlrs.de>
> > To: "Bill Long" <longb at cray.com>
> > Sent: Tuesday, September 9, 2014 5:58:22 PM
> > Subject: Ticket #456 - synchronization in MPI-3.0's shared memory
> > 
> > Dear Bill,
> > 
> > in the Forums discussion on #456
> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/456
> > Bill Gropp had pointed to
> > Hans-J Boehm's paper from 2004:
> > > "Threads Cannot be Implemented as a Library"
> > http://www.hpl.hp.com/techreports/2004/HPL-2004-209.pdf
> > 
> > I've the following question to you as Compiler specialist:
> > 
> > Do we still have the problems in Sections 4.2 and 4.3 of Boehm's
> > paper?
> > 
> > The problem in Section 4.1 is solved as long as the programmer
> > issues
> > memory barriers, which will be synchronization library Routine
> > calls.
> > In C, the opaque library calls should divide conflicting accesses
> > in different
> > access epochs.
> > Same in Fortran with the combination of ASYNCHRONOUS variables and
> > opaque library calls.
> > 
> > If I understand this paper correctly, then the compiler writes
> > since 2004 are
> > aware of applications calling pthreads and therefore, the compilers
> > do not
> > make optimizations that would produce the described data-races in
> > Section
> > 4.2 and 4.3.
> > And of course also other problems detected so far.
> > 
> > Is my assuption correct?
> > 
> > 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)
> > 
> > --
> > 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)
> 

-- 
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)