[mpich-discuss] disable-auto-cleanup send/receive example

[Stewart, Robert]

On 11/02/2011 07:24 PM, Pavan Balaji wrote:

Hi Darius, Pavan,

> In your program, if I added a 
>     sleep(1);
>     MPI_Iprobe(0, 0, MPI_COMM_WORLD, &flag, MPI_STATUS_IGNORE);
> in the error case of the receive, it did run as you expected.  
> There's still a race, it's just less likely to hit in your example.

You're right, that did seem to work. May I ask what the need for the `sleep(1)' is? I'm trying now with another architecture - passing a message round a ring, that is slightly more unpredictable than my previous master/slace example.

Your suggestion does work for that too, but a lot more slowly once a remote process was killed. Is there a possibility to avoid the sleep(1) ? And can you explain for me why the MPI_Iprobe has any effect on fault tolerant behaviour. It does, as you have shown. But I don't know why.

Pavan,

> You cannot just "refresh" MPI_COMM_WORLD by resizing it, as the process 
> ranks will be completely messed up if you do that. What you really want 
> to do is create a new communicator with the remaining "alive" processes. 

That's interesting, this is something I'd like to try. I can't find any compilable examples that make use of MPIX_Group_comm_create, would you be able to provide on? I tried, but wasn't sure how to create/manipulate the MPI_Group, for the 2nd parameter. Are there any code examples?


thanks,

--
Rob Stewart


-- 
Heriot-Watt University is a Scottish charity
registered under charity number SC000278.

Heriot-Watt University is the Sunday Times
Scottish University of the Year 2011-2012


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