Independent write

[Joachim Worringen]

Rob Ross:
> To implement an append mode, there would have to be some sort of
> communication between processes that kept everyone up to date about what
> entry was the "last" one, and some mechanism for ensuring that only one
> process got to write to that position.
>
> That is a generally difficult thing to implement in a low-overhead,
> scalable way, regardless of the API.

One might define an "atomic mode" for pNetCDF, like in MPI-IO. MPI-2 one-sided 
communication could be a way to implement the required synchronization 
(doulbe-locking two windows to access some data in one of the windows 
atomically like fetch&increment - not nice, but works). It's efficiency would 
depend on the progress characteristics of the underlying MPI implementation 
and/or the interconnect and/or the communication behaviour of the 
application, but it would work anyway. As many interconnect today allow RMA, 
the performance of passive synchronization should become better with the MPI 
implementations exploiting such capabilities.

BTW, what's the state of the one-sided communication in MPICH2? ;-)

 Joachim

-- 
Joachim Worringen - NEC C&C research lab St.Augustin
fon +49-2241-9252.20 - fax .99 - http://www.ccrl-nece.de