From f3b8d9de6f7775923a5531a5985ea474bff9cd4e Mon Sep 17 00:00:00 2001
From: mattijs <mattijs>
Date: Wed, 3 Apr 2013 16:30:44 +0100
Subject: [PATCH] ENH: UPstream: extra checking for already clear comms

---
 src/Pstream/mpi/UPstream.C | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index b8bb7ab0c7..1b53aa1566 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -441,9 +441,14 @@ void Foam::UPstream::freePstreamCommunicator(const label communicator)
     {
         if (PstreamGlobals::MPICommunicators_[communicator] != MPI_COMM_NULL)
         {
+            // Free communicator. Sets communicator to MPI_COMM_NULL
             MPI_Comm_free(&PstreamGlobals::MPICommunicators_[communicator]);
         }
-        MPI_Group_free(&PstreamGlobals::MPIGroups_[communicator]);
+        if (PstreamGlobals::MPIGroups_[communicator] != MPI_GROUP_NULL)
+        {
+            // Free greoup. Sets group to MPI_GROUP_NULL
+            MPI_Group_free(&PstreamGlobals::MPIGroups_[communicator]);
+        }
     }
 }