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

[Robert Kubrick]

Thanks Rajeev, I already have the book in the mail. On a related  
note, is there any potential issue using SYSV semaphores with one- 
sided communications? While the active task is completing the set of  
instructions, all the other slave processes could wait on a semaphore.

On Jul 10, 2008, at 4:11 PM, Rajeev Thakur wrote:

> 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?
>>
>>
>