Asychronous Communication

[niklas-uhl]

For the current milestone we focus only on point to point communication

• isend and friends (implemented in Isend #518)
• iprobe (implemented in Add support for iprobe. #521)
• irecv (implemented in Implement irecv #615)

Non-blocking/asynchronous collectives are part of #549

[niklas-uhl]

Replicate the "classic" polling-based approach with a useful interface

• should use same interface as synchronous communication (maybe provide send_sync and send_async)
• wait() with timeouts
• use std::promise and std::future

[niklas-uhl]

I think we want two APIs for working with asynchronous communication:

• request based interface which just returns request objects, which expose wait(), test() etc.
• a future-based interface which allows for chaining. I.e. a call returns a future, when can then transform the result using then() and pass a transformation lambda. The then()-transformations are chained and lazy-evaluated when wait() is called on the future.
  • we can draw inspiration from what UPC++ does (see here and here )
  • This would also be another USP for KaMPIng, MPL only has plain requests, the rwth-mpi implementation only provides rudimentary future support