MPI architecture

[sunsirui]

Hello:
I have one issue about sst-macro's mpi architecture. Collective functional steps of sst-macro design:

1. To create collective active.
2. Algorithm: create some send and recv action, and list them in initial_actions set.
3. Run all actions in a loop.
4. Waiting the collective request.
   But i check in mvapich or in sst-element (firely), collective function steps:
5. algorithm: directly use send, recv, isend, wait or other function through different algorithms.
   So, I mean, why don't we design Collective using the same approach as mvapich or sst-element(firely) ? Does it have some other stragtegies in sst-macro ?