Usage of non-blocking send and blocking receive in MPI?

Question

I am trying to implement master-worker program.

My master has jobs that the workers are going to do. Every time a worker completes a job, he asks for a new job from the master, and the master sends it to him. The workers are calculating minimal paths. When a worker finds a minimum that is better than the global minimum he got, he sends it to everyone including the master.

I plan for the workers and masters to send data using MPI_ISEND. Also, I think that the receive should be blocking. The master has nothing to do when no one has asked for work or has updated the best result, so he should block waiting for a receive. Also, each worker should, after he has done his work, wait on a receive to get a new one.

Nevertheless, I'm not sure of the impact of using non-blocking asynchronous send, and blocking synchronous receive.

An alternative I think is using MPI_IPROBE, but I'm not sure that this will give me any optimization.

Please help me understand whether what I'm doing is right. Is this the right solution?

Answer 1

You can match blocking sends with nonblocking receives and vice versa, that won't cause any problems. However, if the master really has nothing to do while the workers work, and the workers should block after completing their work unit, then there's no reason for non-blocking communication on that front. The master can post a blocking receive with MPI_ANY_SOURCE, and the workers can just use a blocking send to post back their results, since the matching receive at the master will already have been posted.

So, I'd have Send-Recv for exchanging work units between master and worker, and Isend-Irecv for broadcasting the new global minima.