CODEWITHSUNDEEP
c++cparallel-processingmpiopenmpi
Ben Stott
Ben Stott

Reputation: 2218

Non-blocking data sharing through OpenMPI

I'm trying to spread data across multiple workers using OpenMPI, however, I'm doing the data division in a fairly custom way that is not amenable to MPI_Scatter or MPI_Broadcast. What I would like to do is to give each processor some work in a queue (or, some other async mechanism) such that they can do their work on the first chunk of data, take the next chunk, repeat until no more chunks.

I know of MPI_Isend, however if I send data with MPI_Isend I can't modify it until it's finished sending; forcing me to use MPI_Wait and thus having to wait until the thread is finished receiving the data anyway!

Is there a standard a solution to this problem, or must I rethink my approach?

Upvotes: 1

Views: 450

Answers (1)

Wesley Bland
Wesley Bland

Reputation: 9082

Using MPI_ISEND doesn't necessarily mean that the message is received on the remote end. It just means that the buffer is available for reuse. It could be that the message has been buffered internally by Open MPI or that the message actually has been received on the other end. It depends on your message size.

Another option would be to have your workers ask the master process for work when they need it instead of having it pushed to them. Then the master can work only as needed. You could do an MPI_SCATTER for the first message since everyone will be receiving some data. Then after that, have the master do an MPI_RECV(MPI_ANY_SOURCE) to get a message from one of the worker processes.

Upvotes: 1

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