• Type: Correctness / MPI communicator mismatch
• Severity: High
• Component: Neighbor particle CPU MPI path
• Location:
  • Src/Particle/AMReX_NeighborParticlesCPUImpl.H:553
  • Src/Particle/AMReX_NeighborParticlesCPUImpl.H:566

Problem

fillNeighborsMPI() posts receives on ParallelContext::CommunicatorSub():

ParallelDescriptor::Arecv(..., ParallelContext::CommunicatorSub())

but sends payload with default communicator:

ParallelDescriptor::Send(kv.second.data(), Cnt, Who, SeqNum);

This is inconsistent and looks like copy-paste drift (nearby send sites use CommunicatorSub()).

Impact

• In subcommunicator/team execution, sends and receives can target different communicator spaces.
• Can lead to deadlock or unmatched message behavior.

Suggested patch

Use the same subcommunicator for the send call.

--- a/Src/Particle/AMReX_NeighborParticlesCPUImpl.H
+++ b/Src/Particle/AMReX_NeighborParticlesCPUImpl.H
@@
-        ParallelDescriptor::Send(kv.second.data(), Cnt, Who, SeqNum);
+        ParallelDescriptor::Send(kv.second.data(), Cnt, Who, SeqNum,
+                                 ParallelContext::CommunicatorSub());

Prepared by Codex