From f498d09dbfdd1e4da0051d5ef07705a98187052d Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Wed, 16 Jan 2019 21:33:06 +0100
Subject: [PATCH] ENH: add simplified gather methods for globalIndex with
 default communicator

- when combining lists in processor order this simplifies code and
  reduces memory overhead.

  Write this:
    ----
    labelList collected;

    const globalIndex sizing(input.size());
    sizing.gather(input, collected);
    ----

  OR

    ----
    labelList collected;
    globalIndex::gatherOp(input, collected);
    ----

  Instead of this:

    ----
    labelList collected;

    List<labelList> scratch(Pstream::nProcs());
    scratch[Pstream::myProcNo()] = input;
    Pstream::gatherList(scratch);

    if (Pstream::master())
    {
        collected = ListListOps::combine<labelList>
        (
            scratch,
            accessOp<labelList>()
        );
    }
    scratch.clear();
    ----
---
 .../manipulation/checkMesh/checkGeometry.C    |  26 +----
 .../moveDynamicMesh/moveDynamicMesh.C         |  15 +--
 src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H |  36 +++---
 .../polyMesh/globalMeshData/globalIndex.C     |  38 +++---
 .../polyMesh/globalMeshData/globalIndex.H     |  91 ++++++++++++---
 .../polyMesh/globalMeshData/globalIndexI.H    |  18 ++-
 .../globalMeshData/globalIndexTemplates.C     | 109 +++++++++++++++++-
 .../field/AMIWeights/AMIWeights.C             |  26 +----
 .../meshRefinement/meshRefinementTemplates.C  |   8 +-
 9 files changed, 236 insertions(+), 131 deletions(-)

diff --git a/applications/utilities/mesh/manipulation/checkMesh/checkGeometry.C b/applications/utilities/mesh/manipulation/checkMesh/checkGeometry.C
index 5b096c1a87..76f9bbe690 100644
--- a/applications/utilities/mesh/manipulation/checkMesh/checkGeometry.C
+++ b/applications/utilities/mesh/manipulation/checkMesh/checkGeometry.C
@@ -1014,12 +1014,6 @@ Foam::label Foam::checkGeometry
                         scalarField mergedWeights;
                         globalFaces().gather
                         (
-                            UPstream::worldComm,
-                            ListOps::create<label>
-                            (
-                                UPstream::procID(UPstream::worldComm),
-                                labelOp<int>()  // int -> label
-                            ),
                             ami.srcWeightsSum(),
                             mergedWeights
                         );
@@ -1048,18 +1042,14 @@ Foam::label Foam::checkGeometry
                         {
                             const cyclicACMIPolyPatch& pp =
                                 refCast<const cyclicACMIPolyPatch>(pbm[patchi]);
+
                             scalarField mergedMask;
                             globalFaces().gather
                             (
-                                UPstream::worldComm,
-                                ListOps::create<label>
-                                (
-                                    UPstream::procID(UPstream::worldComm),
-                                    labelOp<int>()  // int -> label
-                                ),
                                 pp.mask(),
                                 mergedMask
                             );
+
                             if (Pstream::master())
                             {
                                 wr.write
@@ -1108,12 +1098,6 @@ Foam::label Foam::checkGeometry
                         scalarField mergedWeights;
                         globalFaces().gather
                         (
-                            UPstream::worldComm,
-                            ListOps::create<label>
-                            (
-                                UPstream::procID(UPstream::worldComm),
-                                labelOp<int>()  // int -> label
-                            ),
                             ami.tgtWeightsSum(),
                             mergedWeights
                         );
@@ -1145,12 +1129,6 @@ Foam::label Foam::checkGeometry
                             scalarField mergedMask;
                             globalFaces().gather
                             (
-                                UPstream::worldComm,
-                                ListOps::create<label>
-                                (
-                                    UPstream::procID(UPstream::worldComm),
-                                    labelOp<int>()  // int -> label
-                                ),
                                 pp.neighbPatch().mask(),
                                 mergedMask
                             );
diff --git a/applications/utilities/mesh/manipulation/moveDynamicMesh/moveDynamicMesh.C b/applications/utilities/mesh/manipulation/moveDynamicMesh/moveDynamicMesh.C
index fa73c3d8f3..9f6326277f 100644
--- a/applications/utilities/mesh/manipulation/moveDynamicMesh/moveDynamicMesh.C
+++ b/applications/utilities/mesh/manipulation/moveDynamicMesh/moveDynamicMesh.C
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2016 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2016-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -78,19 +78,10 @@ void writeWeights
         mergedFaces,
         mergedPoints
     );
+
     // Collect field
     scalarField mergedWeights;
-    globalFaces().gather
-    (
-        UPstream::worldComm,
-        ListOps::create<label>
-        (
-            UPstream::procID(UPstream::worldComm),
-            labelOp<int>()  // int -> label
-        ),
-        wghtSum,
-        mergedWeights
-    );
+    globalFaces().gather(wghtSum, mergedWeights);
 
     instant inst(runTime.value(), runTime.timeName());
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
index 10a51a4f97..09cfd7888a 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
@@ -58,7 +58,6 @@ namespace Foam
 
 class UPstream
 {
-
 public:
 
     //- Types of communications
@@ -72,6 +71,7 @@ public:
     //- Names of the communication types
     static const Enum<commsTypes> commsTypeNames;
 
+
     // Public classes
 
         //- Structure for communicating between processors
@@ -159,11 +159,8 @@ public:
 
 
         //- combineReduce operator for lists. Used for counting.
-        class listEq
+        struct listEq
         {
-
-        public:
-
             template<class T>
             void operator()(T& x, const T& y) const
             {
@@ -430,7 +427,7 @@ public:
         }
 
         //- Process index of the master
-        static int masterNo()
+        static constexpr int masterNo() noexcept
         {
             return 0;
         }
@@ -459,7 +456,7 @@ public:
         }
 
         //- Process index of first slave
-        static int firstSlave()
+        static constexpr int firstSlave() noexcept
         {
             return 1;
         }
@@ -495,19 +492,19 @@ public:
         }
 
 
-            //- Get the communications type of the stream
-            commsTypes commsType() const
-            {
-                return commsType_;
-            }
+        //- Get the communications type of the stream
+        commsTypes commsType() const
+        {
+            return commsType_;
+        }
 
-            //- Set the communications type of the stream
-            commsTypes commsType(const commsTypes ct)
-            {
-                commsTypes oldCommsType = commsType_;
-                commsType_ = ct;
-                return oldCommsType;
-            }
+        //- Set the communications type of the stream
+        commsTypes commsType(const commsTypes ct)
+        {
+            commsTypes oldCommsType = commsType_;
+            commsType_ = ct;
+            return oldCommsType;
+        }
 
 
         //- Exit program
@@ -575,6 +572,7 @@ Ostream& operator<<(Ostream&, const UPstream::commsStruct&);
 template<>
 UPstream::commsStruct&
 UList<UPstream::commsStruct>::operator[](const label);
+
 template<>
 const UPstream::commsStruct&
 UList<UPstream::commsStruct>::operator[](const label) const;
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.C b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.C
index 6b4c68d157..eaf95f8c1a 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.C
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.C
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2018-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -74,33 +74,25 @@ void Foam::globalIndex::reset
 }
 
 
-void Foam::globalIndex::reset(const label localSize)
+Foam::labelList Foam::globalIndex::sizes() const
 {
-    offsets_.resize(Pstream::nProcs()+1);
+    labelList values;
 
-    labelList localSizes(Pstream::nProcs(), Zero);
-    localSizes[Pstream::myProcNo()] = localSize;
+    const label len = (offsets_.size() - 1);
 
-    Pstream::gatherList(localSizes, Pstream::msgType());
-    Pstream::scatterList(localSizes, Pstream::msgType());
-
-    label offset = 0;
-    offsets_[0] = 0;
-    for (label proci = 0; proci < Pstream::nProcs(); ++proci)
+    if (len < 1)
     {
-        const label oldOffset = offset;
-        offset += localSizes[proci];
-
-        if (offset < oldOffset)
-        {
-            FatalErrorInFunction
-                << "Overflow : sum of sizes " << localSizes
-                << " exceeds capability of label (" << labelMax
-                << "). Please recompile with larger datatype for label."
-                << exit(FatalError);
-        }
-        offsets_[proci+1] = offset;
+        return values;
     }
+
+    values.resize(len);
+
+    for (label proci=0; proci < len; ++proci)
+    {
+        values[proci] = offsets_[proci+1] - offsets_[proci];
+    }
+
+    return values;
 }
 
 
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.H b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.H
index ff387c3881..25bae51adb 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.H
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.H
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2018-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -108,6 +108,12 @@ public:
         //- Const-access to the offsets
         inline const labelList& offsets() const;
 
+        //- Global sum of localSizes
+        inline label size() const;
+
+        //- The local sizes
+        labelList sizes() const;
+
 
     // Edit
 
@@ -116,7 +122,7 @@ public:
 
         //- Reset from local size.
         //  Does communication with default communicator and message tag.
-        void reset(const label localSize);
+        inline void reset(const label localSize);
 
         //- Reset from local size.
         //  Does communication with given communicator and message tag
@@ -159,9 +165,6 @@ public:
 
         // Global queries
 
-            //- Global sum of localSizes
-            inline label size() const;
-
             //- Start of proci data
             inline label offset(const label proci) const;
 
@@ -236,8 +239,33 @@ public:
                 gather(offsets_, comm, procIDs, fld, allFld, tag, commsType);
             }
 
-            //- Inplace collect data in processor order on master
-            //  (== procIDs[0]). Needs offsets only on master.
+            //- Collect data in processor order on master.
+            //  Does communication with default communicator and message tag.
+            template<class Type>
+            void gather
+            (
+                const UList<Type>& fld,
+                List<Type>& allFld,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes commsType =
+                    Pstream::commsTypes::nonBlocking
+            ) const;
+
+            //- Collect data in processor order on master.
+            //  Does communication with default communicator and message tag.
+            template<class Type>
+            static void gatherOp
+            (
+                const UList<Type>& fld,
+                List<Type>& allFld,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes commsType =
+                    Pstream::commsTypes::nonBlocking
+            );
+
+
+            //- Inplace collect in processor order on master (== procIDs[0]).
+            //- Needs offsets only on master.
             template<class Type>
             static void gather
             (
@@ -250,8 +278,8 @@ public:
                     Pstream::commsTypes::nonBlocking
             );
 
-            //- Inplace collect data in processor order on master
-            //  (== procIDs[0]). Needs offsets only on master.
+            //- Inplace collect in processor order on master (== procIDs[0]).
+            //- Needs offsets only on master.
             template<class Type>
             void gather
             (
@@ -266,6 +294,31 @@ public:
                 gather(offsets_, comm, procIDs, fld, tag, commsType);
             }
 
+            //- Inplace collect data in processor order on master
+            //  Does communication with default communicator and message tag.
+            //  After the gather, the field is zero-sized on the slaves.
+            template<class Type>
+            void gather
+            (
+                List<Type>& fld,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes commsType =
+                    Pstream::commsTypes::nonBlocking
+            ) const;
+
+            //- Inplace collect data in processor order on master
+            //  Does communication with default communicator and message tag.
+            //  After the gather, the field is zero-sized on the slaves.
+            template<class Type>
+            static void gatherOp
+            (
+                List<Type>& fld,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes commsType =
+                    Pstream::commsTypes::nonBlocking
+            );
+
+
             //- Distribute data in processor order. Requires fld to be sized!
             template<class Type>
             static void scatter
@@ -296,6 +349,18 @@ public:
                 scatter(offsets_, comm, procIDs, allFld, fld, tag, commsType);
             }
 
+            //- Distribute data in processor order. Requires fld to be sized!
+            //  Does communication with default communicator and message tag.
+            template<class Type>
+            void scatter
+            (
+                const UList<Type>& allFld,
+                UList<Type>& fld,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes commsType =
+                    Pstream::commsTypes::nonBlocking
+            ) const;
+
 
     // IOstream Operators
 
@@ -310,16 +375,16 @@ public:
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+#include "globalIndexI.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
 #ifdef NoRepository
     #include "globalIndexTemplates.C"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-#include "globalIndexI.H"
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
 #endif
 
 // ************************************************************************* //
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
index b2ae4c4030..709c3421ca 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
@@ -82,6 +82,18 @@ inline Foam::labelList& Foam::globalIndex::offsets()
 }
 
 
+inline Foam::label Foam::globalIndex::size() const
+{
+    return offsets_.empty() ? 0 : offsets_.last();
+}
+
+
+inline void Foam::globalIndex::reset(const label localSize)
+{
+    reset(localSize, Pstream::msgType(), 0, true);
+}
+
+
 inline Foam::label Foam::globalIndex::offset(const label proci) const
 {
     return offsets_[proci];
@@ -124,12 +136,6 @@ inline Foam::labelRange Foam::globalIndex::range() const
 }
 
 
-inline Foam::label Foam::globalIndex::size() const
-{
-    return offsets_.last();
-}
-
-
 inline bool Foam::globalIndex::isLocal(const label proci, const label i) const
 {
     return i >= offsets_[proci] && i < offsets_[proci+1];
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
index de3a7bb9f1..c93727bd3f 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2013-2017 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,7 +52,7 @@ void Foam::globalIndex::gather
          || commsType == Pstream::commsTypes::blocking
         )
         {
-            for (label i = 1; i < procIDs.size(); i++)
+            for (label i = 1; i < procIDs.size(); ++i)
             {
                 SubList<Type> procSlot(allFld, off[i+1]-off[i], off[i]);
 
@@ -96,7 +96,7 @@ void Foam::globalIndex::gather
             label startOfRequests = Pstream::nRequests();
 
             // Set up reads
-            for (label i = 1; i < procIDs.size(); i++)
+            for (label i = 1; i < procIDs.size(); ++i)
             {
                 SubList<Type> procSlot(allFld, off[i+1]-off[i], off[i]);
 
@@ -179,6 +179,40 @@ void Foam::globalIndex::gather
 }
 
 
+template<class Type>
+void Foam::globalIndex::gather
+(
+    const UList<Type>& fld,
+    List<Type>& allFld,
+    const int tag,
+    const Pstream::commsTypes commsType
+) const
+{
+    gather
+    (
+        UPstream::worldComm,
+        identity(Pstream::nProcs(UPstream::worldComm)),
+        fld,
+        allFld,
+        tag,
+        commsType
+    );
+}
+
+
+template<class Type>
+void Foam::globalIndex::gatherOp
+(
+    const UList<Type>& fld,
+    List<Type>& allFld,
+    const int tag,
+    const Pstream::commsTypes commsType
+)
+{
+    globalIndex(fld.size()).gather(fld, allFld, tag, commsType);
+}
+
+
 template<class Type>
 void Foam::globalIndex::gather
 (
@@ -201,6 +235,49 @@ void Foam::globalIndex::gather
 }
 
 
+template<class Type>
+void Foam::globalIndex::gather
+(
+    List<Type>& fld,
+    const int tag,
+    const Pstream::commsTypes commsType
+) const
+{
+    List<Type> allFld;
+
+    gather
+    (
+        UPstream::worldComm,
+        identity(Pstream::master(UPstream::worldComm)),
+        fld,
+        allFld,
+        tag,
+        commsType
+    );
+
+    if (Pstream::master(UPstream::worldComm))
+    {
+        fld.transfer(allFld);
+    }
+    else
+    {
+        fld.clear();
+    }
+}
+
+
+template<class Type>
+void Foam::globalIndex::gatherOp
+(
+    List<Type>& fld,
+    const int tag,
+    const Pstream::commsTypes commsType
+)
+{
+    globalIndex(fld.size()).gather(fld, tag, commsType);
+}
+
+
 template<class Type>
 void Foam::globalIndex::scatter
 (
@@ -223,7 +300,7 @@ void Foam::globalIndex::scatter
          || commsType == Pstream::commsTypes::blocking
         )
         {
-            for (label i = 1; i < procIDs.size(); i++)
+            for (label i = 1; i < procIDs.size(); ++i)
             {
                 const SubList<Type> procSlot
                 (
@@ -272,7 +349,7 @@ void Foam::globalIndex::scatter
             label startOfRequests = Pstream::nRequests();
 
             // Set up writes
-            for (label i = 1; i < procIDs.size(); i++)
+            for (label i = 1; i < procIDs.size(); ++i)
             {
                 const SubList<Type> procSlot
                 (
@@ -360,4 +437,26 @@ void Foam::globalIndex::scatter
 }
 
 
+template<class Type>
+void Foam::globalIndex::scatter
+(
+    const UList<Type>& allFld,
+    UList<Type>& fld,
+    const int tag,
+    const Pstream::commsTypes commsType
+) const
+{
+    scatter
+    (
+        offsets_,
+        UPstream::worldComm,
+        identity(Pstream::nProcs(UPstream::worldComm)),
+        allFld,
+        fld,
+        tag,
+        commsType
+    );
+}
+
+
 // ************************************************************************* //
diff --git a/src/functionObjects/field/AMIWeights/AMIWeights.C b/src/functionObjects/field/AMIWeights/AMIWeights.C
index 8f85c1944e..413b6f93b3 100644
--- a/src/functionObjects/field/AMIWeights/AMIWeights.C
+++ b/src/functionObjects/field/AMIWeights/AMIWeights.C
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+    \\  /    A nd           | Copyright (C) 2018-2019 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -237,17 +237,7 @@ void Foam::functionObjects::AMIWeights::writeWeightField
 
     // Collect field
     scalarField mergedWeights;
-    globalFaces().gather
-    (
-        UPstream::worldComm,
-        ListOps::create<label>
-        (
-            UPstream::procID(UPstream::worldComm),
-            labelOp<int>()  // int -> label
-        ),
-        weightSum,
-        mergedWeights
-    );
+    globalFaces().gather(weightSum, mergedWeights);
 
     const bool isACMI = isA<cyclicACMIPolyPatch>(cpp);
 
@@ -256,17 +246,7 @@ void Foam::functionObjects::AMIWeights::writeWeightField
     {
         const cyclicACMIPolyPatch& pp = refCast<const cyclicACMIPolyPatch>(cpp);
 
-        globalFaces().gather
-        (
-            UPstream::worldComm,
-            ListOps::create<label>
-            (
-                UPstream::procID(UPstream::worldComm),
-                labelOp<int>()  // int -> label
-            ),
-            pp.mask(),
-            mergedMask
-        );
+        globalFaces().gather(pp.mask(), mergedMask);
     }
 
     if (Pstream::master())
diff --git a/src/mesh/snappyHexMesh/meshRefinement/meshRefinementTemplates.C b/src/mesh/snappyHexMesh/meshRefinement/meshRefinementTemplates.C
index 9cba909231..ff7c829fcf 100644
--- a/src/mesh/snappyHexMesh/meshRefinement/meshRefinementTemplates.C
+++ b/src/mesh/snappyHexMesh/meshRefinement/meshRefinementTemplates.C
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2015 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -161,13 +161,11 @@ void Foam::meshRefinement::collectAndPrint
     const UList<T>& data
 )
 {
-    globalIndex globalPoints(points.size());
+    const globalIndex globalPoints(points.size());
 
     pointField allPoints;
     globalPoints.gather
     (
-        Pstream::worldComm,
-        identity(Pstream::nProcs()),
         points,
         allPoints,
         UPstream::msgType(),
@@ -177,8 +175,6 @@ void Foam::meshRefinement::collectAndPrint
     List<T> allData;
     globalPoints.gather
     (
-        Pstream::worldComm,
-        identity(Pstream::nProcs()),
         data,
         allData,
         UPstream::msgType(),