[Mpi3-rma] RMA proposal 1 update

[Rajeev Thakur]

Implementation wise, allowing nested locks (with exclusive) may not be a
trivial change.

Rajeev 

> -----Original Message-----
> From: mpi3-rma-bounces at lists.mpi-forum.org 
> [mailto:mpi3-rma-bounces at lists.mpi-forum.org] On Behalf Of 
> Pavan Balaji
> Sent: Wednesday, May 26, 2010 11:52 AM
> To: MPI 3.0 Remote Memory Access working group
> Subject: Re: [Mpi3-rma] RMA proposal 1 update
> 
> 
> On 05/26/2010 11:40 AM, Rajeev Thakur wrote:
> >> Yes, you do -- so my notes (a) and (b) below are only for the "if 
> >> lockall is only for shared locks" case.
> > 
> > Not just lockall. The user would have to assert that no 
> other process
> > will call regular lock with an exclusive lock.
> 
> Correct. But if it's a different synchronization primitive, we don't 
> have to care about that case.
> 
> >> I think there are two parts here -- (1) to remove the 
> restriction on 
> >> whether only one lock can be acquired; and (2) to provide 
> the lockall 
> >> convenience function.
> >>
> >> (1) is a minor change to the standard and should be included.
> > 
> > If you allow nested locks with exclusive locks, the user code may
> > deadlock depending on what the implementatation chooses to 
> do: block on
> > a lock or defer everything until unlock. The user code may 
> work in some
> > cases, and may not work in other cases.
> 
> That's a user error, and is to be dealt by other tools outside of the 
> scope of MPI.
> 
> There are a lot of ways a user can screw up even within the 
> current MPI 
> standard. We can't drop flexibility because someone might screw up.
> 
>   -- Pavan
> 
> -- 
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji
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