The MPI mode of h5writer assumes the first worker (excluding the Hummingbird master) to be busy-looping for h5 messages. However, Hummingbird itself will assume that to be another consumer of events, just like the other ones. In online operation, this doesn't matter, the other workers on the same node will consume all shmem events. For file-based MPI operation, it is a real problem.
The MPI mode of h5writer assumes the first worker (excluding the Hummingbird master) to be busy-looping for h5 messages. However, Hummingbird itself will assume that to be another consumer of events, just like the other ones. In online operation, this doesn't matter, the other workers on the same node will consume all shmem events. For file-based MPI operation, it is a real problem.