Somehow there is no comment field on your MPI BOF page.....

Scenario: root process sends request to all others and post a receive from any source. All other processes calculate and post Isend with result. Root receives one result and then broadcasts that it doesn't need the rest any more. All other processes see this broadcast, and cancel their sends if they have been performed already. If their calculation was not finished yet, they abort it.

Somehow I find a cancelled send request much more natural than a cancelled receive.....