ENH: globalIndex gather/scatter scheduled (not nonBlocking) for non-contiguous

- reduces later surprises and simplifies effort for the caller

- more flexible globalIndex scatter with auto-sized return field.

- Avoid communication for scattering into zero-sized fields.

src/OpenFOAM/parallel/globalIndex/globalIndex.C

@@ -34,16 +34,16 @@ License
 void Foam::globalIndex::reportOverflowAndExit
 (
     const label idx,
-    const labelUList& localSizes
+    const labelUList& localLens
 )
 {
     FatalErrorInFunction
         << "Overflow : sum of sizes exceeds labelMax ("
         << labelMax << ") after index " << idx;
 
-    if (!localSizes.empty())
+    if (!localLens.empty())
     {
-        FatalError << " of " << flatOutput(localSizes);
+        FatalError << " of " << flatOutput(localLens);
     }
 
     FatalError
@@ -56,13 +56,13 @@ void Foam::globalIndex::reportOverflowAndExit
 Foam::labelList
 Foam::globalIndex::calcOffsets
 (
-    const labelUList& localSizes,
+    const labelUList& localLens,
     const bool checkOverflow
 )
 {
     labelList values;
 
-    const label len = localSizes.size();
+    const label len = localLens.size();
 
     if (len)
     {
@@ -72,11 +72,11 @@ Foam::globalIndex::calcOffsets
         for (label i = 0; i < len; ++i)
         {
             values[i] = start;
-            start += localSizes[i];
+            start += localLens[i];
 
             if (checkOverflow && start < values[i])
             {
-                reportOverflowAndExit(i, localSizes);
+                reportOverflowAndExit(i, localLens);
             }
         }
         values[len] = start;
@@ -89,13 +89,13 @@ Foam::globalIndex::calcOffsets
 Foam::List<Foam::labelRange>
 Foam::globalIndex::calcRanges
 (
-    const labelUList& localSizes,
+    const labelUList& localLens,
     const bool checkOverflow
 )
 {
     List<labelRange> values;
 
-    const label len = localSizes.size();
+    const label len = localLens.size();
 
     if (len)
     {
@@ -104,12 +104,12 @@ Foam::globalIndex::calcRanges
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
-            values[i].reset(start, localSizes[i]);
-            start += localSizes[i];
+            values[i].reset(start, localLens[i]);
+            start += localLens[i];
 
             if (checkOverflow && start < values[i].start())
             {
-                reportOverflowAndExit(i, localSizes);
+                reportOverflowAndExit(i, localLens);
             }
         }
     }
@@ -221,16 +221,16 @@ void Foam::globalIndex::reset
         // Seed with localSize, zero elsewhere (for non-parallel branch)
         // NB: can consider UPstream::listGatherValues
 
-        labelList localSizes(len, Zero);
-        localSizes[Pstream::myProcNo(comm)] = localSize;
+        labelList localLens(len, Zero);
+        localLens[Pstream::myProcNo(comm)] = localSize;
 
         if (parallel)
         {
-            Pstream::gatherList(localSizes, tag, comm);
-            Pstream::scatterList(localSizes, tag, comm);
+            Pstream::gatherList(localLens, tag, comm);
+            Pstream::scatterList(localLens, tag, comm);
         }
 
-        reset(localSizes, true);  // checkOverflow = true
+        reset(localLens, true);  // checkOverflow = true
     }
     else
     {
@@ -242,11 +242,11 @@ void Foam::globalIndex::reset
 
 void Foam::globalIndex::reset
 (
-    const labelUList& localSizes,
+    const labelUList& localLens,
     const bool checkOverflow
 )
 {
-    const label len = localSizes.size();
+    const label len = localLens.size();
 
     if (len)
     {
@@ -256,11 +256,11 @@ void Foam::globalIndex::reset
         for (label i = 0; i < len; ++i)
         {
             offsets_[i] = start;
-            start += localSizes[i];
+            start += localLens[i];
 
             if (checkOverflow && start < offsets_[i])
             {
-                reportOverflowAndExit(i, localSizes);
+                reportOverflowAndExit(i, localLens);
             }
         }
         offsets_[len] = start;
@@ -290,7 +290,7 @@ void Foam::globalIndex::setLocalSize(const label proci, const label len)
 }
 
 
-Foam::labelList Foam::globalIndex::sizes() const
+Foam::labelList Foam::globalIndex::localSizes() const
 {
     labelList values;
 

src/OpenFOAM/parallel/globalIndex/globalIndex.H

@@ -89,7 +89,7 @@ class globalIndex
         static void reportOverflowAndExit
         (
             const label idx,
-            const labelUList& localSizes = labelUList::null()
+            const labelUList& localLens = labelUList::null()
         );
 
 public:
@@ -178,12 +178,15 @@ public:
         //- Global sum of localSizes.
         inline label totalSize() const;
 
-        //- The local sizes
-        labelList sizes() const;
+        //- The local sizes. Same as localSizes()
+        inline labelList sizes() const;
 
         //- The local starts
         inline const labelUList localStarts() const;
 
+        //- The local sizes
+        labelList localSizes() const;
+
         //- Global max of localSizes
         inline label maxSize() const;
 
@@ -276,7 +279,7 @@ public:
             inline labelList toGlobal(const labelUList& labels) const;
 
             //- From local to global index (inplace)
-            inline void inplaceToGlobal(labelList& labels) const;
+            inline void inplaceToGlobal(labelUList& labels) const;
 
             //- From global to local on current processor.
             //  FatalError if not on local processor.
@@ -314,7 +317,7 @@ public:
             inline void inplaceToGlobal
             (
                 const label proci,
-                labelList& labels
+                labelUList& labels
             ) const;
 
 
@@ -405,7 +408,7 @@ public:
         //- with optional check for label overflow
         static labelList calcOffsets
         (
-            const labelUList& localSizes,
+            const labelUList& localLens,
             const bool checkOverflow = false
         );
 
@@ -422,7 +425,7 @@ public:
         //- with optional check for label overflow
         static List<labelRange> calcRanges
         (
-            const labelUList& localSizes,
+            const labelUList& localLens,
             const bool checkOverflow = false
         );
 
@@ -774,8 +777,21 @@ public:
             template<class Type>
             void scatter
             (
-                const UList<Type>& allFld,
-                UList<Type>& fld,
+                const UList<Type>& allData,
+                UList<Type>& localData,
+                const int tag = UPstream::msgType(),
+                const Pstream::commsTypes = Pstream::commsTypes::nonBlocking,
+                const label comm = UPstream::worldComm  //!< communicator
+            ) const;
+
+            //- Distribute data in processor order
+            //- (in serial: performs a simple copy).
+            //  Communication with default/specified communicator, message tag.
+            //  \note the globalIndex offsets needed on master only.
+            template<class Type, class OutputContainer = List<Type>>
+            OutputContainer scatter
+            (
+                const UList<Type>& allData,
                 const int tag = UPstream::msgType(),
                 const Pstream::commsTypes = Pstream::commsTypes::nonBlocking,
                 const label comm = UPstream::worldComm  //!< communicator

src/OpenFOAM/parallel/globalIndex/globalIndexI.H

@@ -142,6 +142,12 @@ inline Foam::label Foam::globalIndex::size() const
 }
 
 
+inline Foam::labelList Foam::globalIndex::sizes() const
+{
+    return localSizes();
+}
+
+
 inline Foam::label Foam::globalIndex::nProcs() const noexcept
 {
     const label len = (offsets_.size() - 1);
@@ -289,7 +295,7 @@ inline Foam::labelList Foam::globalIndex::toGlobal
 inline void Foam::globalIndex::inplaceToGlobal
 (
     const label proci,
-    labelList& labels
+    labelUList& labels
 ) const
 {
     const label off = offsets_[proci];
@@ -301,7 +307,7 @@ inline void Foam::globalIndex::inplaceToGlobal
 }
 
 
-inline void Foam::globalIndex::inplaceToGlobal(labelList& labels) const
+inline void Foam::globalIndex::inplaceToGlobal(labelUList& labels) const
 {
     inplaceToGlobal(Pstream::myProcNo(), labels);
 }

src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C

@@ -73,22 +73,22 @@ void Foam::globalIndex::gather
     const UList<Type>& fld,
     List<Type>& allFld,
     const int tag,
-    const Pstream::commsTypes commsType
+    const Pstream::commsTypes preferredCommsType
 )
 {
     // low-level: no parRun guard
 
-    if
+    // Automatically change from nonBlocking to scheduled for
+    // non-contiguous data.
+    const UPstream::commsTypes commsType =
     (
-        !is_contiguous<Type>::value
-     && commsType == Pstream::commsTypes::nonBlocking
-    )
-    {
-        FatalErrorInFunction
-            << "Cannot use nonBlocking with non-contiguous data"
-            << exit(FatalError);
-        // Could also warn and change to scheduled etc...
-    }
+        (
+            !is_contiguous<Type>::value
+         && UPstream::commsTypes::nonBlocking == preferredCommsType
+        )
+      ? UPstream::commsTypes::scheduled
+      : preferredCommsType
+    );
 
     const label startOfRequests = UPstream::nRequests();
 
@@ -126,14 +126,7 @@ void Foam::globalIndex::gather
             }
             else
             {
-                IPstream fromProc
-                (
-                    commsType,
-                    procIDs[i],
-                    0,
-                    tag,
-                    comm
-                );
+                IPstream fromProc(commsType, procIDs[i], 0, tag, comm);
                 fromProc >> procSlot;
             }
         }
@@ -158,14 +151,7 @@ void Foam::globalIndex::gather
         }
         else
         {
-            OPstream toMaster
-            (
-                commsType,
-                procIDs[0],
-                0,
-                tag,
-                comm
-            );
+            OPstream toMaster(commsType, procIDs[0], 0, tag, comm);
             toMaster << fld;
         }
     }
@@ -187,18 +173,22 @@ void Foam::globalIndex::gather
     const IndirectListBase<Type, Addr>& fld,
     List<Type>& allFld,
     const int tag,
-    const Pstream::commsTypes commsType
+    const Pstream::commsTypes preferredCommsType
 )
 {
     // low-level: no parRun guard
 
-    if (commsType == Pstream::commsTypes::nonBlocking)
-    {
-        WarningInFunction
-            << "Cannot use nonBlocking with indirect list of data"
-            << exit(FatalError);
-        // Could also warn and change to scheduled etc...
-    }
+    // Automatically change from nonBlocking to scheduled for
+    // non-contiguous data.
+    const UPstream::commsTypes commsType =
+    (
+        (
+            !is_contiguous<Type>::value
+         && UPstream::commsTypes::nonBlocking == preferredCommsType
+        )
+      ? UPstream::commsTypes::scheduled
+      : preferredCommsType
+    );
 
     if (Pstream::myProcNo(comm) == procIDs[0])
     {
@@ -224,14 +214,7 @@ void Foam::globalIndex::gather
             }
             else
             {
-                IPstream fromProc
-                (
-                    commsType,
-                    procIDs[i],
-                    0,
-                    tag,
-                    comm
-                );
+                IPstream fromProc(commsType, procIDs[i], 0, tag, comm);
                 fromProc >> procSlot;
             }
         }
@@ -244,14 +227,7 @@ void Foam::globalIndex::gather
         }
         else
         {
-            OPstream toMaster
-            (
-                commsType,
-                procIDs[0],
-                0,
-                tag,
-                comm
-            );
+            OPstream toMaster(commsType, procIDs[0], 0, tag, comm);
             toMaster << fld;
         }
     }
@@ -692,20 +668,22 @@ void Foam::globalIndex::scatter
     const UList<Type>& allFld,
     UList<Type>& fld,
     const int tag,
-    const Pstream::commsTypes commsType
+    const Pstream::commsTypes preferredCommsType
 )
 {
-    if
+    // low-level: no parRun guard
+
+    // Automatically change from nonBlocking to scheduled for
+    // non-contiguous data.
+    const UPstream::commsTypes commsType =
     (
-        !is_contiguous<Type>::value
-     && commsType == Pstream::commsTypes::nonBlocking
-    )
-    {
-        FatalErrorInFunction
-            << "Cannot use nonBlocking with non-contiguous data"
-            << exit(FatalError);
-        // Could also warn and change to scheduled etc...
-    }
+        (
+            !is_contiguous<Type>::value
+         && UPstream::commsTypes::nonBlocking == preferredCommsType
+        )
+      ? UPstream::commsTypes::scheduled
+      : preferredCommsType
+    );
 
     // FUTURE:
     // could decide which procs will receive data and use mpiScatter
@@ -715,18 +693,15 @@ void Foam::globalIndex::scatter
 
     if (Pstream::myProcNo(comm) == procIDs[0])
     {
-        const SubList<Type> localSlot(allFld, off[1]-off[0], off[0]);
-
-        if (!localSlot.empty())
-        {
-            fld.deepCopy(localSlot);
-        }
-
         for (label i = 1; i < procIDs.size(); ++i)
         {
             const SubList<Type> procSlot(allFld, off[i+1]-off[i], off[i]);
 
-            if (is_contiguous<Type>::value)
+            if (procSlot.empty())
+            {
+                // Nothing to do
+            }
+            else if (is_contiguous<Type>::value)
             {
                 OPstream::write
                 (
@@ -740,21 +715,30 @@ void Foam::globalIndex::scatter
             }
             else
             {
-                OPstream toProc
-                (
-                    commsType,
-                    procIDs[i],
-                    0,
-                    tag,
-                    comm
-                );
+                OPstream toProc(commsType, procIDs[i], 0, tag, comm);
                 toProc << procSlot;
             }
         }
+
+        // Assign my local data - respect offset information
+        // so that we can request 0 entries to be copied.
+        // Also handle the case where we have a slice of the full
+        // list.
+
+        SubList<Type>(fld, off[1]-off[0]) =
+            SubList<Type>(allFld, off[1]-off[0], off[0]);
     }
     else
     {
-        if (is_contiguous<Type>::value)
+        // Note: we are receiving into UList, so sizes MUST match or we
+        // have a problem. Can therefore reasonably assume that a zero-sized
+        // send matches a zero-sized receive, and we can skip that.
+
+        if (fld.empty())
+        {
+            // Nothing to do
+        }
+        else if (is_contiguous<Type>::value)
         {
             IPstream::read
             (
@@ -768,14 +752,7 @@ void Foam::globalIndex::scatter
         }
         else
         {
-            IPstream fromMaster
-            (
-                commsType,
-                procIDs[0],
-                0,
-                tag,
-                comm
-            );
+            IPstream fromMaster(commsType, procIDs[0], 0, tag, comm);
             fromMaster >> fld;
         }
     }
@@ -791,26 +768,64 @@ void Foam::globalIndex::scatter
 template<class Type>
 void Foam::globalIndex::scatter
 (
-    const UList<Type>& allFld,
-    UList<Type>& fld,
+    const UList<Type>& allData,
+    UList<Type>& localData,
     const int tag,
     const Pstream::commsTypes commsType,
     const label comm
 ) const
 {
-    // TBD: protection and special handling for serial?
+    if (UPstream::parRun())
     {
         scatter
         (
             offsets_,  // needed on master only
             comm,
             UPstream::procID(comm),
-            allFld,
-            fld,
+            allData,
+            localData,
             tag,
             commsType
         );
     }
+    else
+    {
+        // Serial: direct copy
+        // - fails miserably if incorrectly dimensioned!
+        localData.deepCopy(allData);
+    }
+}
+
+
+template<class Type, class OutputContainer>
+OutputContainer Foam::globalIndex::scatter
+(
+    const UList<Type>& allData,
+    const int tag,
+    const Pstream::commsTypes commsType,
+    const label comm
+) const
+{
+    if (UPstream::parRun())
+    {
+        // The globalIndex might be correct on master only,
+        // so scatter local sizes to ensure consistency
+
+        const label localLen
+        (
+            UPstream::listScatterValues<label>(this->localSizes(), comm)
+        );
+
+        OutputContainer localData(localLen);
+        this->scatter(allData, localData, tag, commsType, comm);
+
+        return localData;
+    }
+    else
+    {
+        // Serial: direct copy
+        return OutputContainer(allData);
+    }
 }