bugfix for freeing MPI communicators every balance

include/ALL_Histogram.hpp

@@ -70,13 +70,22 @@ public:
 
     // array of MPI communicators for each direction (to collect work
     // on each plane)
-    communicators.resize(2 * this->dimension);
+    communicators.resize(6);
+    for (int i=0; i<6; i++) communicators.at(i) = MPI_COMM_NULL;
+
     nNeighbors.resize(2 * this->dimension);
     nBins.resize(this->dimension);
   }
 
   /// default destructor
-  ~Histogram_LB() = default;
+  ~Histogram_LB() {
+    for (int i=0; i<communicators.size(); i++) {
+      if (communicators.at(i) != MPI_COMM_NULL &&
+          communicators.at(i) != MPI_COMM_SELF &&
+          communicators.at(i) != MPI_COMM_WORLD)
+        MPI_Comm_free(&(communicators.at(i)));
+    }
+  }
 
   /// method to setup the loac-balancing method
   void setup() override;
@@ -156,6 +165,14 @@ template <class T, class W> void Histogram_LB<T, W>::setup() {
   // get the local rank from the MPI communicator
   MPI_Cart_rank(this->globalComm, this->local_coords.data(), &this->localRank);
 
+  // free sub-communicators
+  for (int i=0; i<6; i++) {
+    if (communicators.at(i) != MPI_COMM_SELF &&
+        communicators.at(i) != MPI_COMM_WORLD &&
+        communicators.at(i) != MPI_COMM_NULL)
+      MPI_Comm_free(&(communicators.at(i)));
+  }
+
   // create sub-communicators
 
   // communicators 0 - 2: reduction of partial histograms
@@ -358,14 +375,6 @@ template <class T, class W> void Histogram_LB<T, W>::balance(int step) {
               << std::endl;
 
   find_neighbors();
-
-  MPI_Barrier(this->globalComm);
-  // free created communicators
-  for (int i = 0; i < 6; ++i) {
-    if (communicators.at(i) != MPI_COMM_SELF &&
-        communicators.at(i) != MPI_COMM_WORLD)
-      MPI_Comm_free(&(communicators.at(i)));
-  }
 }
 
 template <class T, class W> void Histogram_LB<T, W>::find_neighbors() {