[Mpi-forum] MPI_Win_lock_all() ordering question

[Michael Raymond]

   Thanks. Searching the tickets just now, I found #363. Are my issue 
and that ticket related?

https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/363

On 07/17/2013 10:54 AM, Jim Dinan wrote:
> Hi Michael,
>
> This believe that this can deadlock.  I agree that it's unfortunate that
> we didn't call it out in the spec, given that it would help to clarify
> the intended semantics.
>
>   ~Jim.
>
>
> On Wed, Jul 17, 2013 at 11:41 AM, Michael Raymond <mraymond at sgi.com
> <mailto:mraymond at sgi.com>> wrote:
>
>        I've got a question about the use of MPI_Win_lock_all() in the
>     face of competing MPI_Win_lock(EXCLUSIVE) calls. Consider the
>     following calls sequence:
>
>
>     0                                                       1
>     MPI_Win_lock(EXCLUSIVE, 0)
>
>     MPI_Win_lock(EXCLUSIVE, 1)              MPI_Win_lock_all()
>
>     ....                                                    ....
>     MPI_Win_unlock(1)                               MPI_Win_unlock_all()
>     MPI_Win_unlock(0)
>
>        In this situation 0 has an exclusive lock on itself.
>     Simultaneously, 0 tries to get 1 exclusively and 1 tries to get a
>     shared lock on everyone. If 0 gets lucky, it will get to go first
>     and everything will go fine. If OTOH 1 locks itself shared and then
>     tries to lock 0 shared, deadlock ensues. You could argue that there
>     should be some global queue / governor that lets 0 go first, but
>     then I could see running into scalability problems.
>
>        I can't find any place in the standard that says if the user
>     shouldn't do this, or if deadlock is allowed, or if the MPI
>     implementation should figure things out on its own. Thoughts?
>
>     --
>     Michael A. Raymond
>     SGI MPT Team Leader
>     (651) 683-3434
>
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-- 
Michael A. Raymond
SGI MPT Team Leader
(651) 683-3434