[mpich-discuss] lock/unlock regions and process synchronization

[Rajeev Thakur]

What you are trying to do is an atomic read-modify-write, which is not
trivial to do with the MPI-2 one-sided operations. There are two ways
described in the book, Using MPI-2. One is easier to understand than the
other one, but is less scalable. The source code for both is available in
the MPICH2 distribution. See fetchandadd.c and fetchandadd_tree.c in
test/mpi/rma.

Rajeev 

> -----Original Message-----
> From: owner-mpich-discuss at mcs.anl.gov 
> [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Robert Kubrick
> Sent: Thursday, July 10, 2008 3:04 PM
> To: mpich-discuss at mcs.anl.gov
> Subject: [mpich-discuss] lock/unlock regions and process 
> synchronization
> 
> I need to access a one-sided window region in a master from multiple  
> slave processes. Each slave needs to read the window contents, then  
> update the same window area:
> 
> MPI_Win_lock(...);
> MPI_Get(&idx, ...);
> MPI_Win_unlock(...);
> 
> // Got idx, check value
> if( idx > 10 ) {
>    idx += 5;
>    MPI_Win_lock(...);
>    MPI_Put(&idx);
>    MPI_Win_unlock(...);
> }
> 
> How can I make sure another process does not access 'idx' 
> between the  
> two lock/unlock regions in the example? 
> 
>