From 624b6a72b8cfe1e0083947acb816e9c527251a60 Mon Sep 17 00:00:00 2001
From: Hrvoje Jasak <h.jasak@wikki.co.uk>
Date: Mon, 17 Jun 2019 18:16:26 +0100
Subject: [PATCH] Rewrite of parallel gather-write of immersed boundary patch
 data

---
 .../immersedBoundaryFieldBase.C               | 71 ++++++++++++++-----
 1 file changed, 53 insertions(+), 18 deletions(-)

diff --git a/src/immersedBoundary/immersedBoundary/immersedBoundaryFvPatchFields/immersedBoundaryFieldBase/immersedBoundaryFieldBase.C b/src/immersedBoundary/immersedBoundary/immersedBoundaryFvPatchFields/immersedBoundaryFieldBase/immersedBoundaryFieldBase.C
index 526b1402a..d54ef9552 100644
--- a/src/immersedBoundary/immersedBoundary/immersedBoundaryFvPatchFields/immersedBoundaryFieldBase/immersedBoundaryFieldBase.C
+++ b/src/immersedBoundary/immersedBoundary/immersedBoundaryFvPatchFields/immersedBoundaryFieldBase/immersedBoundaryFieldBase.C
@@ -107,30 +107,65 @@ void Foam::immersedBoundaryFieldBase<Type>::writeField
         if (Pstream::master())
         {
             // Assemble unique lists to correspond to a single surface
-            pointField allPoints(0);
-            Field<Type> completeField(0);
-            faceList allFaces(0);
-            label prevProcPatchSize = 0;
 
-            forAll(procPoints, procI)
+            // Count points and faces; currently unmerged
+            label nAllPoints = 0;
+            label nAllFaces = 0;
+
+            forAll (procPoints, procI)
             {
-                allPoints.append(procPoints[procI]);
-                completeField.append(procFields[procI]);
+                nAllPoints += procPoints[procI].size();
+                nAllFaces += procFaces[procI].size();
+            }
 
-                // Point labels in faces need to be incremented with respect to
-                // the size of the size of the previous processore patch
-                forAll(procFaces[procI], faceI)
+            pointField allPoints(nAllPoints);
+            faceList allFaces(nAllFaces);
+            Field<Type> completeField(nAllFaces);
+
+            // Reset counters
+            nAllPoints = 0;
+            nAllFaces = 0;
+
+            forAll (procPoints, procI)
+            {
+                const pointField& curPoints = procPoints[procI];
+                labelList renumberPoints(curPoints.size());
+
+                forAll (curPoints, cpI)
                 {
-                    face curFace = procFaces[procI][faceI];
-                    forAll(curFace, pointI)
-                    {
-                        curFace[pointI] += prevProcPatchSize;
-                    }
-                    allFaces.append(curFace);
+                    allPoints[nAllPoints] = curPoints[cpI];
+                    renumberPoints[cpI] = nAllPoints;
+                    nAllPoints++;
                 }
 
-                // Increment the total number of points
-                prevProcPatchSize += procPoints[procI].size();
+                const faceList& curFaces = procFaces[procI];
+                const Field<Type>& curField = procFields[procI];
+
+                forAll (curFaces, cfI)
+                {
+                    // Point labels in faces need to be renumbered with respect
+                    // to the size of the size of the previous processore patch
+                    const face& oldFace = curFaces[cfI];
+
+                    // Make a copy of face to renumber
+                    face renumberedFace(oldFace.size());
+
+                    forAll (oldFace, fpI)
+                    {
+                        renumberedFace[fpI] = renumberPoints[oldFace[fpI]];
+                    }
+
+                    allFaces[nAllFaces] = renumberedFace;
+                    completeField[nAllFaces] = curField[cfI];
+                    nAllFaces++;
+                }
+            }
+
+            if (nAllPoints != allPoints.size() || nAllFaces != allFaces.size())
+            {
+                FatalErrorInFunction
+                    << "Problem with merge of immersed boundary patch data"
+                    << abort(FatalError);
             }
 
             writerPtr->write