ENH: extend mpiAllGather to include integer and float types

- was previously limited to 'char' whereas gatherv/scatterv
  already supported various integer and float types

STYLE: rebundle allToAll declarations with macros

ENH: provide a version of allToAllConsensus returning the Map

- simplifies use and avoids ambiguities in the send/recv parameters

- the Map version will now also transmit zero value data if they exist
  in the Map. Unlike the List version, zero values are not necessary to
  signal connectivity with a Map.

COMP: forwarding template parameters for NBX routines

ENH: consolidate PstreamBuffers size exchange options

- had a variety of nearly identical backends for all-to-all,
  gather/scatter. Now combined internally with a dispatch enumeration
  which provides better control over which size exchange algorithm
  is used.

DEFEATURE: remove experimental full-NBX PstreamBuffers variant

- no advantages seen compared to the hybrid NBX/PEX approach.
  Removal reduces some code cruft.

DEFEATURE: remove experimental "double non-blocking" NBX version

- the idea was to avoid blocking receives for very large data transfers,
  but that is usually better accomplished with a hybrid NBX/PEX approach
  like PstreamBuffers allows

etc/controlDict

@@ -1,7 +1,7 @@
 /*--------------------------------*- C++ -*----------------------------------*\
 | =========                 |                                                 |
 | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
-|  \\    /   O peration     | Version:  v2306                                 |
+|  \\    /   O peration     | Version:  v2312                                 |
 |   \\  /    A nd           | Website:  www.openfoam.com                      |
 |    \\/     M anipulation  |                                                 |
 \*---------------------------------------------------------------------------*/
@@ -174,12 +174,13 @@ OptimisationSwitches
     nbx.tuning      0;
 
     // Additional PstreamBuffers tuning parameters (experimental)
-    //   -1 : PEX with all-to-all for buffer sizes and point-to-point
+    //    0 : (legacy PEX)
-    //        for contents (legacy approach)
+    //        * all-to-all for buffer sizes [legacy approach]
-    //    0 : hybrid PEX with NBX for buffer sizes and point-to-point
+    //        * point-to-point for contents
-    //        for contents (proposed new approach)
+    //    1 : (hybrid PEX)
-    //    1 : full NBX for buffer sizes and contents (very experimental)
+    //        * NBX for buffer sizes [new approach]
-    pbufs.tuning   -1;
+    //        * point-to-point for contents
+    pbufs.tuning    0;
 
 
     // =====

src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H

@@ -599,7 +599,7 @@ public:
 
     // Non-blocking exchange
 
-        //- Exchange \em contiguous data using non-blocking consensus
+        //- Exchange \em contiguous data using non-blocking consensus (NBX)
         //- Sends sendData, receives into recvData.
         //
         //  Each entry of the recvBufs list is cleared before receipt.
@@ -614,10 +614,10 @@ public:
             List<Container>& recvBufs,
             const int tag,
             const label comm,
-            const bool wait = true  //!< Wait for requests to complete
+            const bool wait = true  //!< (ignored)
         );
 
-        //- Exchange \em contiguous data using non-blocking consensus
+        //- Exchange \em contiguous data using non-blocking consensus (NBX)
         //- Sends sendData, receives into recvData.
         //
         //  Each \em entry of the recvBufs map is cleared before receipt,
@@ -636,7 +636,23 @@ public:
             Map<Container>& recvBufs,
             const int tag,
             const label comm,
-            const bool wait = true  //!< Wait for requests to complete
+            const bool wait = true  //!< (ignored)
+        );
+
+        //- Exchange \em contiguous data using non-blocking consensus (NBX)
+        //- Sends sendData returns receive information.
+        //
+        //  For \b non-parallel : copy own rank (if it exists and non-empty)
+        //
+        //  \note The message tag should be chosen to be a unique value
+        //  since the implementation uses probing with ANY_SOURCE !!
+        template<class Container, class Type>
+        static Map<Container> exchangeConsensus
+        (
+            const Map<Container>& sendBufs,
+            const int tag,
+            const label comm,
+            const bool wait = true  //!< (ignored)
         );
 };
 

src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C

@@ -36,7 +36,7 @@ License
 int Foam::PstreamBuffers::algorithm
 (
     // Name may change in the future (JUN-2023)
-    Foam::debug::optimisationSwitch("pbufs.tuning", -1)
+    Foam::debug::optimisationSwitch("pbufs.tuning", 0)
 );
 registerOptSwitch
 (
@@ -46,20 +46,19 @@ registerOptSwitch
 );
 
 
-// Simple enumerations
-// -------------------
-static constexpr int algorithm_PEX_allToAll = -1;  // Traditional PEX
-//static constexpr int algorithm_PEX_hybrid = 0;   // Possible new default?
-static constexpr int algorithm_full_NBX = 1;       // Very experimental
-
-
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
+inline void Foam::PstreamBuffers::setFinished(bool on) noexcept
+{
+    finishedSendsCalled_ = on;
+}
+
+
 inline void Foam::PstreamBuffers::initFinalExchange()
 {
     // Could also check that it is not called twice
     // but that is used for overlapping send/recv (eg, overset)
-    finishedSendsCalled_ = true;
+    setFinished(true);
 
     clearUnregistered();
 }
@@ -67,56 +66,121 @@ inline void Foam::PstreamBuffers::initFinalExchange()
 
 void Foam::PstreamBuffers::finalExchange
 (
+    enum modeOption mode,
     const bool wait,
     labelList& recvSizes
 )
 {
     initFinalExchange();
 
-    if (commsType_ == UPstream::commsTypes::nonBlocking)
+    // Pre-flight checks
+    switch (mode)
     {
-        if
+        case modeOption::DEFAULT :
-        (
-            wait
-         && (algorithm >= algorithm_full_NBX)
-         && (UPstream::maxCommsSize <= 0)
-        )
         {
-            // NBX algorithm (nonblocking exchange)
+            // Choose (ALL_TO_ALL | NBX_PEX) from static settings
-            // - when requested and waiting, no data chunking etc
+            mode =
-
-            PstreamDetail::exchangeConsensus<DynamicList<char>, char>
             (
-                sendBuffers_,
+                (algorithm <= 0)
-                recvBuffers_,
+              ? modeOption::ALL_TO_ALL
-                recvSizes,
+              : modeOption::NBX_PEX
-                (tag_ + 271828),  // some unique tag?
-                comm_,
-                wait
             );
+            break;
+        }
 
-            return;
+        case modeOption::GATHER :
+        {
+            // gather mode (all-to-one) : master [0] <- everyone
+            // - only send to master [0]
+            // note: master [0] is also allowed to 'send' to itself
+
+            for (label proci = 1; proci < sendBuffers_.size(); ++proci)
+            {
+                sendBuffers_[proci].clear();
+            }
+            break;
+        }
+
+        case modeOption::SCATTER :
+        {
+            // scatter mode (one-to-all) : master [0] -> everyone
+
+            if (!UPstream::master(comm_))
+            {
+                // Non-master: has no sends
+                clearSends();
+            }
+            break;
+        }
+
+        default :
+            break;
     }
 
 
-        // PEX algorithm with two different flavours of exchanging sizes
+    if (commsType_ == UPstream::commsTypes::nonBlocking)
+    {
+        // PEX algorithm with different flavours of exchanging sizes
+        // PEX stage 1: exchange sizes
 
+        labelList sendSizes;  // Not used by gather/scatter
+
+        switch (mode)
+        {
+            case modeOption::GATHER :
+            {
+                // gather mode (all-to-one): master [0] <- everyone
+                // - presumed that MPI_Gather will be the most efficient
+
+                recvSizes =
+                    UPstream::listGatherValues(sendBuffers_[0].size(), comm_);
+
+                if (!UPstream::master(comm_))
+                {
+                    recvSizes.resize_nocopy(nProcs_);
+                    recvSizes = Zero;
+                }
+
+                break;
+            }
+
+            case modeOption::SCATTER :
+            {
+                // scatter mode (one-to-all): master [0] -> everyone
+                // - presumed that MPI_Scatter will be the most efficient
+
+                recvSizes.resize_nocopy(nProcs_);
+
+                if (UPstream::master(comm_))
+                {
+                    forAll(sendBuffers_, proci)
+                    {
+                        recvSizes[proci] = sendBuffers_[proci].size();
+                    }
+                }
+
+                const label myRecv
+                (
+                    UPstream::listScatterValues(recvSizes, comm_)
+                );
+
+                recvSizes = Zero;
+                recvSizes[0] = myRecv;
+
+                break;
+            }
+
+            case modeOption::NBX_PEX :
+            {
                 // Assemble the send sizes (cf. Pstream::exchangeSizes)
-        labelList sendSizes(nProcs_);
+                sendSizes.resize_nocopy(nProcs_);
                 forAll(sendBuffers_, proci)
                 {
                     sendSizes[proci] = sendBuffers_[proci].size();
                 }
                 recvSizes.resize_nocopy(nProcs_);
 
-        if (algorithm == algorithm_PEX_allToAll)
+                // Exchange sizes (non-blocking consensus)
-        {
-            // PEX stage 1: exchange sizes (all-to-all)
-            UPstream::allToAll(sendSizes, recvSizes, comm_);
-        }
-        else
-        {
-            // PEX stage 1: exchange sizes (non-blocking consensus)
                 UPstream::allToAllConsensus
                 (
                     sendSizes,
@@ -124,8 +188,27 @@ void Foam::PstreamBuffers::finalExchange
                     (tag_ + 314159),  // some unique tag?
                     comm_
                 );
+                break;
             }
 
+            case modeOption::DEFAULT :
+            case modeOption::ALL_TO_ALL :
+            {
+                // Assemble the send sizes (cf. Pstream::exchangeSizes)
+                sendSizes.resize_nocopy(nProcs_);
+                forAll(sendBuffers_, proci)
+                {
+                    sendSizes[proci] = sendBuffers_[proci].size();
+                }
+                recvSizes.resize_nocopy(nProcs_);
+
+                // Exchange sizes (all-to-all)
+                UPstream::allToAll(sendSizes, recvSizes, comm_);
+                break;
+            }
+        }
+
+
         // PEX stage 2: point-to-point data exchange
         Pstream::exchange<DynamicList<char>, char>
         (
@@ -200,93 +283,6 @@ void Foam::PstreamBuffers::finalExchange
 }
 
 
-void Foam::PstreamBuffers::finalGatherScatter
-(
-    const bool isGather,
-    const bool wait,
-    labelList& recvSizes
-)
-{
-    initFinalExchange();
-
-    if (isGather)
-    {
-        // gather mode (all-to-one)
-
-        // Only send to master [0]. Master is also allowed to 'send' to itself
-
-        for (label proci=1; proci < sendBuffers_.size(); ++proci)
-        {
-            sendBuffers_[proci].clear();
-        }
-    }
-    else
-    {
-        // scatter mode (one-to-all)
-
-        if (!UPstream::master(comm_))
-        {
-            // Non-master: has no sends
-            clearSends();
-        }
-    }
-
-
-    if (commsType_ == UPstream::commsTypes::nonBlocking)
-    {
-        // Use PEX algorithm
-        // - for a non-sparse gather/scatter, it is presumed that
-        // MPI_Gather/MPI_Scatter will be the most efficient way to
-        // communicate the sizes.
-
-        // PEX stage 1: exchange sizes (gather or scatter)
-        if (isGather)
-        {
-            // gather mode (all-to-one): master [0] <- everyone
-
-            recvSizes =
-                UPstream::listGatherValues(sendBuffers_[0].size(), comm_);
-
-            if (!UPstream::master(comm_))
-            {
-                recvSizes.resize_nocopy(nProcs_);
-                recvSizes = Zero;
-            }
-        }
-        else
-        {
-            // scatter mode (one-to-all): master [0] -> everyone
-
-            recvSizes.resize_nocopy(nProcs_);
-
-            if (UPstream::master(comm_))
-            {
-                forAll(sendBuffers_, proci)
-                {
-                    recvSizes[proci] = sendBuffers_[proci].size();
-                }
-            }
-
-            const label myRecv(UPstream::listScatterValues(recvSizes, comm_));
-
-            recvSizes = Zero;
-            recvSizes[0] = myRecv;
-        }
-
-        // PEX stage 2: point-to-point data exchange
-        Pstream::exchange<DynamicList<char>, char>
-        (
-            sendBuffers_,
-            recvSizes,
-            recvBuffers_,
-            tag_,
-            comm_,
-            wait
-        );
-    }
-}
-
-
 // * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
 
 Foam::PstreamBuffers::PstreamBuffers
@@ -382,7 +378,7 @@ void Foam::PstreamBuffers::clear()
 {
     clearSends();
     clearRecvs();
-    finishedSendsCalled_ = false;
+    setFinished(false);
 }
 
 
@@ -431,13 +427,13 @@ void Foam::PstreamBuffers::clearStorage()
     }
     recvPositions_ = Zero;
 
-    finishedSendsCalled_ = false;
+    setFinished(false);
 }
 
 
 void Foam::PstreamBuffers::initRegisterSend()
 {
-    if (!finishedSendsCalled_)
+    if (!finished())
     {
         for (label proci = 0; proci < nProcs_; ++proci)
         {
@@ -474,7 +470,7 @@ bool Foam::PstreamBuffers::hasSendData() const
 
 bool Foam::PstreamBuffers::hasRecvData() const
 {
-    if (finishedSendsCalled_)
+    if (finished())
     {
         forAll(recvBuffers_, proci)
         {
@@ -504,7 +500,7 @@ Foam::label Foam::PstreamBuffers::sendDataCount(const label proci) const
 
 Foam::label Foam::PstreamBuffers::recvDataCount(const label proci) const
 {
-    if (finishedSendsCalled_)
+    if (finished())
     {
         const label len(recvBuffers_[proci].size() - recvPositions_[proci]);
 
@@ -529,7 +525,7 @@ Foam::labelList Foam::PstreamBuffers::recvDataCounts() const
 {
     labelList counts(nProcs_, Zero);
 
-    if (finishedSendsCalled_)
+    if (finished())
     {
         forAll(recvBuffers_, proci)
         {
@@ -560,7 +556,7 @@ Foam::label Foam::PstreamBuffers::maxNonLocalRecvCount
 {
     label maxLen = 0;
 
-    if (finishedSendsCalled_)
+    if (finished())
     {
         forAll(recvBuffers_, proci)
         {
@@ -599,7 +595,7 @@ Foam::label Foam::PstreamBuffers::maxNonLocalRecvCount() const
 const Foam::UList<char>
 Foam::PstreamBuffers::peekRecvData(const label proci) const
 {
-    if (finishedSendsCalled_)
+    if (finished())
     {
         const label pos = recvPositions_[proci];
         const label len = recvBuffers_[proci].size();
@@ -625,18 +621,17 @@ Foam::PstreamBuffers::peekRecvData(const label proci) const
 }
 
 
-bool Foam::PstreamBuffers::allowClearRecv(bool on) noexcept
-{
-    bool old(allowClearRecv_);
-    allowClearRecv_ = on;
-    return old;
-}
-
-
 void Foam::PstreamBuffers::finishedSends(const bool wait)
 {
     labelList recvSizes;
-    finalExchange(wait, recvSizes);
+    finalExchange(modeOption::DEFAULT, wait, recvSizes);
+}
+
+
+void Foam::PstreamBuffers::finishedSendsNBX(const bool wait)
+{
+    labelList recvSizes;
+    finalExchange(modeOption::NBX_PEX, wait, recvSizes);
 }
 
 
@@ -649,7 +644,7 @@ void Foam::PstreamBuffers::finishedSends
     // Resize for copying back
     recvSizes.resize_nocopy(sendBuffers_.size());
 
-    finalExchange(wait, recvSizes);
+    finalExchange(modeOption::DEFAULT, wait, recvSizes);
 
     if (commsType_ != UPstream::commsTypes::nonBlocking)
     {
@@ -717,8 +712,9 @@ bool Foam::PstreamBuffers::finishedSends
     if (changed)
     {
         // Update send/recv topology
+
         labelList recvSizes;
-        finishedSends(recvSizes, wait);  // eg, using all-to-all
+        finishedSends(recvSizes, wait);  // modeOption::DEFAULT (eg all-to-all)
 
         // The send ranks
         sendProcs.clear();
@@ -754,14 +750,14 @@ bool Foam::PstreamBuffers::finishedSends
 void Foam::PstreamBuffers::finishedGathers(const bool wait)
 {
     labelList recvSizes;
-    finalGatherScatter(true, wait, recvSizes);
+    finalExchange(modeOption::GATHER, wait, recvSizes);
 }
 
 
 void Foam::PstreamBuffers::finishedScatters(const bool wait)
 {
     labelList recvSizes;
-    finalGatherScatter(false, wait, recvSizes);
+    finalExchange(modeOption::SCATTER, wait, recvSizes);
 }
 
 
@@ -771,7 +767,7 @@ void Foam::PstreamBuffers::finishedGathers
     const bool wait
 )
 {
-    finalGatherScatter(true, wait, recvSizes);
+    finalExchange(modeOption::GATHER, wait, recvSizes);
 
     if (commsType_ != UPstream::commsTypes::nonBlocking)
     {
@@ -793,7 +789,7 @@ void Foam::PstreamBuffers::finishedScatters
     const bool wait
 )
 {
-    finalGatherScatter(false, wait, recvSizes);
+    finalExchange(modeOption::SCATTER, wait, recvSizes);
 
     if (commsType_ != UPstream::commsTypes::nonBlocking)
     {
@@ -809,4 +805,27 @@ void Foam::PstreamBuffers::finishedScatters
 }
 
 
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Controls
+
+bool Foam::PstreamBuffers::finished() const noexcept
+{
+    return finishedSendsCalled_;
+}
+
+
+bool Foam::PstreamBuffers::allowClearRecv() const noexcept
+{
+    return allowClearRecv_;
+}
+
+
+bool Foam::PstreamBuffers::allowClearRecv(bool on) noexcept
+{
+    bool old(allowClearRecv_);
+    allowClearRecv_ = on;
+    return old;
+}
+
+
 // ************************************************************************* //

src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H

@@ -32,7 +32,7 @@ Description
 
     Use UOPstream to stream data into buffers, call finishedSends() to
     notify that data is in buffers and then use IUPstream to get data out
-    of received buffers. Works with both blocking and nonBlocking. Does
+    of received buffers. Works with both blocking and non-blocking. Does
     not make much sense with scheduled since there you would not need these
     explicit buffers.
 
@@ -151,6 +151,19 @@ class bitSet;
 
 class PstreamBuffers
 {
+    // Private Data Types
+
+        //- Private enumeration for handling PEX stage 1 (sizing) modes
+        enum class modeOption : unsigned char
+        {
+            DEFAULT,    //!< Use statically configured algorithm
+            GATHER,     //!< Use all-to-one (gather) of sizes
+            SCATTER,    //!< Use one-to-all (scatter) of sizes
+            ALL_TO_ALL, //!< Use allToAll to obtain sizes
+            NBX_PEX     //!< Use consensus exchange (NBX) to obtain sizes
+        };
+
+
     // Private Data
 
         //- Track if sends are complete
@@ -190,20 +203,24 @@ class PstreamBuffers
 
     // Private Member Functions
 
+        //- Change status of finished sends called
+        inline void setFinished(bool on) noexcept;
+
         //- Clear 'unregistered' send buffers, tag as being send-ready
         inline void initFinalExchange();
 
         //- Mark all sends as having been done.
-        //  This will start receives (nonBlocking comms).
+        //  This will start receives (non-blocking comms).
         void finalExchange
         (
+            enum modeOption mode,
             const bool wait,
             labelList& recvSizes
         );
 
         //- Mark sends as done.
         //  Only exchange sizes using the neighbour ranks
-        //  (nonBlocking comms).
+        //  (non-blocking comms).
         void finalExchange
         (
             const labelUList& sendProcs,
@@ -212,14 +229,6 @@ class PstreamBuffers
             labelList& recvSizes
         );
 
-        //- For all-to-one or one-to-all
-        void finalGatherScatter
-        (
-            const bool isGather,
-            const bool wait,
-            labelList& recvSizes
-        );
-
 
     // Friendship Access
 
@@ -343,17 +352,11 @@ public:
     // Queries
 
         //- True if finishedSends() or finishedNeighbourSends() has been called
-        bool finished() const noexcept
+        bool finished() const noexcept;
-        {
-            return finishedSendsCalled_;
-        }
 
         //- Is clearStorage of individual receive buffer by external hooks
         //- allowed? (default: true)
-        bool allowClearRecv() const noexcept
+        bool allowClearRecv() const noexcept;
-        {
-            return allowClearRecv_;
-        }
 
         //- True if any (local) send buffers have data
         bool hasSendData() const;
@@ -436,74 +439,96 @@ public:
 
     // Regular Functions
 
-        //- Mark sends as done
+        //- Mark the send phase as being finished.
         //
-        //  Non-blocking mode: populates receive buffers (all-to-all).
+        //  Non-blocking mode: populates receive buffers using all-to-all
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        //  or NBX (depending on tuning parameters).
+        //  \param wait wait for requests to complete (in non-blocking mode)
         void finishedSends(const bool wait = true);
 
-        //- Mark sends as done.
+        //- Mark the send phase as being finished.
+        //
+        //  Non-blocking mode: populates receive buffers using NBX.
+        //  \param wait wait for requests to complete (in non-blocking mode)
+        void finishedSendsNBX(const bool wait = true);
+
+        //- Mark the send phase as being finished.
         //- Recovers the sizes (bytes) received.
         //
-        //  Non-blocking mode: populates receive buffers (all-to-all).
+        //  Non-blocking mode: populates receive buffers using all-to-all
-        //  \param[out] recvSizes the sizes (bytes) received
+        //  or NBX (depending on tuning parameters).
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        //  \warning currently only valid for non-blocking comms.
+        void finishedSends
+        (
+            //! [out] the sizes (bytes) received
+            labelList& recvSizes,
+            //! wait for requests to complete (in non-blocking mode)
+            const bool wait = true
+        );
+
+        //- Mark the send phase as being finished.
+        //- Recovers the sizes (bytes) received.
         //
-        //  \warning currently only valid for nonBlocking comms.
+        //  Non-blocking mode: populates receive buffers using NBX.
-        void finishedSends(labelList& recvSizes, const bool wait = true);
+        //  \warning currently only valid for non-blocking comms.
+        void finishedSendsNBX
+        (
+            //! [out] the sizes (bytes) received
+            labelList& recvSizes,
+            //! wait for requests to complete (in non-blocking mode)
+            const bool wait = true
+        );
 
 
     // Functions with restricted neighbours
 
-        //- Mark sends as done using subset of send/recv ranks
+        //- Mark the send phase as being finished, with communication
-        //- and recover the sizes (bytes) received.
+        //- being limited to a known subset of send/recv ranks.
         //
         //  Non-blocking mode: populates receive buffers.
         //
-        //  \param neighProcs ranks used for sends/recvs
+        //  \warning currently only valid for non-blocking comms.
-        //  \param wait wait for requests to complete (in nonBlocking mode)
-        //
-        //  \warning currently only valid for nonBlocking comms.
         //  \note Same as finishedSends with identical sendProcs/recvProcs
         void finishedNeighbourSends
         (
+            //! ranks used for sends/recvs
             const labelUList& neighProcs,
+            //! wait for requests to complete (in non-blocking mode)
             const bool wait = true
         );
 
-        //- Mark sends as done using subset of send/recv ranks
+        //- Mark the send phase as being finished, with communication
-        //- and recover the sizes (bytes) received.
+        //- being limited to a known subset of send/recv ranks.
+        //- Recovers the sizes (bytes) received.
         //
         //  Non-blocking mode: it will populate receive buffers.
         //
-        //  \param neighProcs ranks used for sends/recvs
+        //  \warning currently only valid for non-blocking mode.
-        //  \param[out] recvSizes the sizes (bytes) received
-        //  \param wait wait for requests to complete (in nonBlocking mode)
-        //
-        //  \warning currently only valid for nonBlocking mode.
         void finishedNeighbourSends
         (
+            //! ranks used for sends/recvs
             const labelUList& neighProcs,
+            //! [out] the sizes (bytes) received
             labelList& recvSizes,
+            //! wait for requests to complete (in non-blocking mode)
             const bool wait = true
         );
 
         //- A caching version that uses a limited send/recv connectivity.
         //
         //  Non-blocking mode: populates receive buffers.
-        //  \param sendConnections on/off for sending ranks
-        //  \param sendProcs ranks used for sends
-        //  \param recvProcs ranks used for recvs
-        //  \param wait wait for requests to complete (in nonBlocking mode)
-        //
         //  \return True if the send/recv connectivity changed
         //
-        //  \warning currently only valid for nonBlocking comms.
+        //  \warning currently only valid for non-blocking comms.
         bool finishedSends
         (
+            //! inter-rank connections (on/off) for sending ranks
             bitSet& sendConnections,
+            //! ranks used for sends
             DynamicList<label>& sendProcs,
+            //! ranks used for recvs
             DynamicList<label>& recvProcs,
+            //! wait for requests to complete (in non-blocking mode)
             const bool wait = true
         );
 
@@ -515,40 +540,46 @@ public:
         //  Non-blocking mode: populates receive buffers.
         //  Can use recvDataCount, maxRecvCount etc to recover sizes received.
         //
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        //  \param wait wait for requests to complete (in non-blocking mode)
         //
-        //  \warning currently only valid for nonBlocking comms.
+        //  \warning currently only valid for non-blocking comms.
         void finishedGathers(const bool wait = true);
 
         //- Mark all sends to master as done.
         //- Recovers the sizes (bytes) received.
         //
         //  Non-blocking mode: populates receive buffers (all-to-one).
-        //  \param[out] recvSizes the sizes (bytes) received
+        //  \warning currently only valid for non-blocking comms.
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        void finishedGathers
-        //
+        (
-        //  \warning currently only valid for nonBlocking comms.
+            //! [out] the sizes (bytes) received
-        void finishedGathers(labelList& recvSizes, const bool wait = true);
+            labelList& recvSizes,
+            //! wait for requests to complete (in non-blocking mode)
+            const bool wait = true
+        );
 
         //- Mark all sends to sub-procs as done.
         //
         //  Non-blocking mode: populates receive buffers.
         //  Can use recvDataCount, maxRecvCount etc to recover sizes received.
         //
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        //  \param wait wait for requests to complete (in non-blocking mode)
         //
-        //  \warning currently only valid for nonBlocking comms.
+        //  \warning currently only valid for non-blocking comms.
         void finishedScatters(const bool wait = true);
 
         //- Mark all sends to sub-procs as done.
         //- Recovers the sizes (bytes) received.
         //
         //  Non-blocking mode: populates receive buffers (all-to-one).
-        //  \param[out] recvSizes the sizes (bytes) received
+        //  \warning currently only valid for non-blocking comms.
-        //  \param wait wait for requests to complete (in nonBlocking mode)
+        void finishedScatters
-        //
+        (
-        //  \warning currently only valid for nonBlocking comms.
+            //! [out] the sizes (bytes) received
-        void finishedScatters(labelList& recvSizes, const bool wait = true);
+            labelList& recvSizes,
+            //! wait for requests to complete (in non-blocking mode)
+            const bool wait = true
+        );
 };
 
 

src/OpenFOAM/db/IOstreams/Pstreams/PstreamExchangeConsensus.C

@@ -46,21 +46,19 @@ namespace Foam
 namespace PstreamDetail
 {
 
-//- Exchange \em contiguous data using non-blocking consensus exchange
+//- Exchange \em contiguous data using non-blocking consensus exchange (NBX)
 //- with optional tracking of the receive sizes.
 //
 //  No internal guards or resizing - data containers are all properly
 //  sized before calling.
 //
-//  \param[in]  sendBufs  The send buffers list (size: numProcs)
+//  \param[in]  sendBufs  The send buffers list (size: numProc)
-//  \param[out] recvBufs  The recv buffers list (size: numProcs)
+//  \param[out] recvBufs  The recv buffers list (size: numProc)
-//  \param[out] recvSizes The recv sizes (size: 0 or numProcs).
+//  \param[out] recvSizes The recv sizes (size: 0 or numProc).
 //     This parameter can be an empty list, in which case the receive sizes
 //     are not returned.
 //  \param tag   The message tag
 //  \param comm  The communicator
-//  \param wait  Wait for non-blocking receives to complete
-//  \param recvCommType If blocking or (default) non-blocking
 
 template<class Container, class Type>
 void exchangeConsensus
@@ -69,20 +67,17 @@ void exchangeConsensus
     UList<Container>& recvBufs,
     labelUList& recvSizes,
     const int tag,
-    const label comm,
+    const label comm
-    const bool wait = true,
-    const UPstream::commsTypes recvCommType = UPstream::commsTypes::nonBlocking
 )
 {
     static_assert(is_contiguous<Type>::value, "Contiguous data only!");
 
     const bool initialBarrier = (UPstream::tuning_NBX_ > 0);
 
-    const label startOfRequests = UPstream::nRequests();
     const label myProci = UPstream::myProcNo(comm);
     const label numProc = UPstream::nProcs(comm);
 
-    // Initial: clear all receive information
+    // Initial: clear all receive locations
     for (auto& buf : recvBufs)
     {
         buf.clear();
@@ -98,28 +93,37 @@ void exchangeConsensus
     if (sendBufs.size() > numProc)
     {
         FatalErrorInFunction
-            << "Send buffers:" << sendBufs.size() << " > numProcs:" << numProc
+            << "Send buffers:" << sendBufs.size() << " > numProc:" << numProc
             << Foam::abort(FatalError);
     }
     if (recvBufs.size() < numProc)
     {
         FatalErrorInFunction
-            << "Recv buffers:" << recvBufs.size() << " < numProcs:" << numProc
+            << "Recv buffers:" << recvBufs.size() << " < numProc:" << numProc
             << Foam::abort(FatalError);
     }
     // #endif
 
-    if (!UPstream::is_parallel(comm))
+    // Fake send/recv for myself - parallel or non-parallel
     {
-        // Do myself
         recvBufs[myProci] = sendBufs[myProci];
         if (myProci < recvSizes.size())
         {
             recvSizes[myProci] = recvBufs.size();
         }
+    }
+
+    if (!UPstream::is_parallel(comm))
+    {
+        // Nothing left to do
         return;
     }
 
+
+    // ------------------------------------------------------------------------
+    // Setup sends
+    // ------------------------------------------------------------------------
+
     // An initial barrier may help to avoid synchronisation problems
     // caused elsewhere
     if (initialBarrier)
@@ -127,11 +131,12 @@ void exchangeConsensus
         UPstream::barrier(comm);
     }
 
+
     // Algorithm NBX: Nonblocking consensus with List containers
 
     DynamicList<UPstream::Request> sendRequests(sendBufs.size());
 
-    // Start nonblocking synchronous send to processor dest
+    // Start nonblocking synchronous send to destination ranks
     for (label proci = 0; proci < numProc; ++proci)
     {
         const auto& sendData = sendBufs[proci];
@@ -140,19 +145,8 @@ void exchangeConsensus
         {
             // Do not send/recv empty data
         }
-        else if (proci == myProci)
+        else if (proci != myProci)
         {
-            // Do myself
-            recvBufs[proci] = sendData;
-            if (proci < recvSizes.size())
-            {
-                recvSizes[proci] = sendData.size();
-            }
-        }
-        else
-        {
-            // Has data to send.
-            // The MPI send requests are tracked on a local list
             UOPstream::write
             (
                 sendRequests.emplace_back(),
@@ -167,7 +161,15 @@ void exchangeConsensus
     }
 
 
+    // ------------------------------------------------------------------------
     // Probe and receive
+    // ------------------------------------------------------------------------
+    //
+    // When receiving can use resize() instead of resize_nocopy() since the
+    // slots were already initially cleared.
+    // The resize() also works fine with FixedList since it will
+    // corresponds to a no-op: send and recv sizes will always be
+    // identical to its fixed size() / max_size()
 
     UPstream::Request barrierRequest;
 
@@ -191,17 +193,16 @@ void exchangeConsensus
             const label count = (probed.second / sizeof(Type));
 
             auto& recvData = recvBufs[proci];
-            recvData.resize_nocopy(count);
+            recvData.resize(count);  // OK with resize() instead of _nocopy()
 
             if (proci < recvSizes.size())
             {
                 recvSizes[proci] = count;
             }
 
-            // Any non-blocking MPI recv requests are tracked on internal stack
             UIPstream::read
             (
-                recvCommType,
+                UPstream::commsTypes::blocking,
                 proci,
                 recvData.data_bytes(),
                 recvData.size_bytes(),
@@ -229,26 +230,18 @@ void exchangeConsensus
             }
         }
     }
-
-    // Wait for non-blocking receives to finish
-    if (wait && recvCommType == UPstream::commsTypes::nonBlocking)
-    {
-        UPstream::waitRequests(startOfRequests);
-    }
 }
 
 
-//- Exchange \em contiguous data using non-blocking consensus exchange.
+//- Exchange \em contiguous data using non-blocking consensus exchange (NBX)
 //
 //  No internal guards - the sending Map corresponds to a segment of
-//  0-numProcs.
+//  0-numProc.
 //
-//  \param[in]  sendBufs  The send buffers map (addr: 0-numProcs)
+//  \param[in]  sendBufs  The send buffers map (addr: 0-numProc)
 //  \param[out] recvBufs  The recv buffers map
 //  \param tag   The message tag
 //  \param comm  The communicator
-//  \param wait  Wait for non-blocking receives to complete
-//  \param recvCommType If blocking or (default) non-blocking
 
 template<class Container, class Type>
 void exchangeConsensus
@@ -256,17 +249,17 @@ void exchangeConsensus
     const Map<Container>& sendBufs,
     Map<Container>& recvBufs,
     const int tag,
-    const label comm,
+    const label comm
-    const bool wait = true,
-    const UPstream::commsTypes recvCommType = UPstream::commsTypes::nonBlocking
 )
 {
     static_assert(is_contiguous<Type>::value, "Contiguous data only!");
 
-    const label startOfRequests = UPstream::nRequests();
+    // TDB: const bool initialBarrier = (UPstream::tuning_NBX_ > 0);
-    const label myProci = UPstream::myProcNo(comm);
 
-    // Initial: clear out receive 'slots'
+    const label myProci = UPstream::myProcNo(comm);
+    const label numProc = UPstream::myProcNo(comm);
+
+    // Initial: clear all receive locations
     // Preferrable to clear out the map entries instead of the map itself
     // since this can potentially preserve allocated space
     // (eg DynamicList entries) between calls
@@ -276,9 +269,13 @@ void exchangeConsensus
         iter.val().clear();
     }
 
-    if (!UPstream::is_parallel(comm))
+    if (!UPstream::is_rank(comm))
+    {
+        return;  // Process not in communicator
+    }
+
+    // Fake send/recv for myself - parallel or non-parallel
     {
-        // Do myself
         const auto iter = sendBufs.find(myProci);
         if (iter.good())
         {
@@ -290,43 +287,38 @@ void exchangeConsensus
                 recvBufs(iter.key()) = sendData;
             }
         }
+    }
+
+    if (!UPstream::is_parallel(comm))
+    {
+        // Nothing left to do
         return;
     }
 
 
+    // ------------------------------------------------------------------------
+    // Setup sends
+    // ------------------------------------------------------------------------
+
+    // TDB: initialBarrier ...
+
+
     // Algorithm NBX: Nonblocking consensus with Map (HashTable) containers
 
     DynamicList<UPstream::Request> sendRequests(sendBufs.size());
 
-    // Start nonblocking synchronous send to process dest
+    // Start nonblocking synchronous send to destination ranks
     forAllConstIters(sendBufs, iter)
     {
         const label proci = iter.key();
         const auto& sendData = iter.val();
 
-        #ifdef FULLDEBUG
+        if (sendData.empty() || proci < 0 || proci >= numProc)
-        if (proci >= UPstream::nProcs(comm))
         {
-            FatalErrorInFunction
+            // Do not send/recv empty data or invalid destinations
-                << "Send buffer:" << proci << " >= numProcs:"
-                << UPstream::nProcs(comm)
-                << Foam::abort(FatalError);
         }
-        #endif
+        else if (proci != myProci)
-
-        if (sendData.empty())
         {
-            // Do not send/recv empty data
-        }
-        else if (proci == myProci)
-        {
-            // Do myself: insert_or_assign
-            recvBufs(proci) = sendData;
-        }
-        else
-        {
-            // Has data to send.
-            // The MPI send requests are tracked on a local list
             UOPstream::write
             (
                 sendRequests.emplace_back(),
@@ -341,7 +333,15 @@ void exchangeConsensus
     }
 
 
+    // ------------------------------------------------------------------------
     // Probe and receive
+    // ------------------------------------------------------------------------
+    //
+    // When receiving can use resize() instead of resize_nocopy() since the
+    // slots were already initially cleared.
+    // The resize() also works fine with FixedList since it will
+    // corresponds to a no-op: send and recv sizes will always be
+    // identical to its fixed size() / max_size()
 
     UPstream::Request barrierRequest;
 
@@ -365,12 +365,11 @@ void exchangeConsensus
             const label count = (probed.second / sizeof(Type));
 
             auto& recvData = recvBufs(proci);
-            recvData.resize_nocopy(count);
+            recvData.resize(count);  // OK with resize() instead of _nocopy()
 
-            // Any non-blocking MPI recv requests are tracked on internal stack
             UIPstream::read
             (
-                recvCommType,
+                UPstream::commsTypes::blocking,
                 proci,
                 recvData.data_bytes(),
                 recvData.size_bytes(),
@@ -397,12 +396,6 @@ void exchangeConsensus
             }
         }
     }
-
-    // Wait for non-blocking receives to finish
-    if (wait && recvCommType == UPstream::commsTypes::nonBlocking)
-    {
-        UPstream::waitRequests(startOfRequests);
-    }
 }
 
 } // namespace PstreamDetail
@@ -418,7 +411,7 @@ void Foam::Pstream::exchangeConsensus
     List<Container>& recvBufs,
     const int tag,
     const label comm,
-    const bool wait
+    const bool /* wait (ignored) */
 )
 {
     static_assert(is_contiguous<Type>::value, "Contiguous data only!");
@@ -427,7 +420,7 @@ void Foam::Pstream::exchangeConsensus
     {
         FatalErrorInFunction
             << "Send buffers size:" << sendBufs.size()
-            << " != numProcs:" << UPstream::nProcs(comm)
+            << " != numProc:" << UPstream::nProcs(comm)
             << Foam::abort(FatalError);
     }
 
@@ -435,14 +428,13 @@ void Foam::Pstream::exchangeConsensus
     recvBufs.resize_nocopy(sendBufs.size());
     labelList dummyRecvSizes;
 
-    PstreamDetail::exchangeConsensus
+    PstreamDetail::exchangeConsensus<Container, Type>
     (
         sendBufs,
         recvBufs,
         dummyRecvSizes,
         tag,
-        comm,
+        comm
-        wait
     );
 }
 
@@ -454,20 +446,45 @@ void Foam::Pstream::exchangeConsensus
     Map<Container>& recvBufs,
     const int tag,
     const label comm,
-    const bool wait
+    const bool  /* wait (ignored) */
 )
 {
     static_assert(is_contiguous<Type>::value, "Contiguous data only!");
 
-    PstreamDetail::exchangeConsensus
+    PstreamDetail::exchangeConsensus<Container, Type>
     (
         sendBufs,
         recvBufs,
         tag,
-        comm,
+        comm
-        wait
     );
 }
 
 
+template<class Container, class Type>
+Foam::Map<Container>
+Foam::Pstream::exchangeConsensus
+(
+    const Map<Container>& sendBufs,
+    const int tag,
+    const label comm,
+    const bool  /* wait (ignored) */
+)
+{
+    Map<Container> recvBufs;
+
+    static_assert(is_contiguous<Type>::value, "Contiguous data only!");
+
+    PstreamDetail::exchangeConsensus<Container, Type>
+    (
+        sendBufs,
+        recvBufs,
+        tag,
+        comm
+    );
+
+    return recvBufs;
+}
+
+
 // ************************************************************************* //

src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H

@@ -44,6 +44,7 @@ SourceFiles
 #include "labelList.H"
 #include "DynamicList.H"
 #include "HashTable.H"
+#include "Map.H"
 #include "Enum.H"
 #include "ListOps.H"
 
@@ -55,9 +56,6 @@ namespace Foam
 //- Implementation details for UPstream/Pstream/MPI etc.
 namespace PstreamDetail {}
 
-// Forward Declarations
-template<class T> class Map;
-
 /*---------------------------------------------------------------------------*\
                           Class UPstream Declaration
 \*---------------------------------------------------------------------------*/
@@ -968,119 +966,76 @@ public:
         //- Shutdown (finalize) MPI as required and exit program with errNo.
         static void exit(int errNo = 1);
 
-        //- Exchange integer data with all processors (in the communicator).
-        //  \c sendData[proci] is the value to send to proci.
-        //  After return recvData contains the data from the other processors.
-        //  \n
-        //  For \b non-parallel : does a simple copy of sendData to recvData
-        static void allToAll
-        (
-            const UList<int32_t>& sendData,
-            UList<int32_t>& recvData,
-            const label communicator = worldComm
-        );
 
-        //- Exchange integer data with all processors (in the communicator).
+        #undef  Pstream_CommonRoutines
-        //  \c sendData[proci] is the value to send to proci.
+        #define Pstream_CommonRoutines(Native)                                \
-        //  After return recvData contains the data from the other processors.
+                                                                              \
-        //  \n
+        /*!\brief Exchange \c Native data with all ranks in communicator   */ \
-        //  For \b non-parallel : does a simple copy of sendData to recvData
+        /*! \em non-parallel : simple copy of \p sendData to \p recvData   */ \
-        static void allToAll
+        static void allToAll                                                  \
-        (
+        (                                                                     \
-            const UList<int64_t>& sendData,
+            /*! [in] The value at [proci] is sent to proci */                 \
-            UList<int64_t>& recvData,
+            const UList<Native>& sendData,                                    \
-            const label communicator = worldComm
+            /*! [out] The data received from the other ranks */               \
-        );
+            UList<Native>& recvData,                                          \
+            const label communicator = worldComm                              \
+        );                                                                    \
+                                                                              \
+        /*!\brief Exchange \em non-zero \c Native data between ranks [NBX] */ \
+        /*! \p recvData is always initially assigned zero and no non-zero  */ \
+        /*! values are sent/received from other ranks.                     */ \
+        /*! \em non-parallel : simple copy of \p sendData to \p recvData   */ \
+        /*! \note The message tag should be chosen to be a unique value    */ \
+        /*! since the implementation uses probing with ANY_SOURCE !!       */ \
+        /*! An initial barrier may help to avoid synchronisation problems  */ \
+        /*! caused elsewhere (See "nbx.tuning" opt switch)                 */ \
+        static void allToAllConsensus                                         \
+        (                                                                     \
+            /*! [in] The \em non-zero value at [proci] is sent to proci */    \
+            const UList<Native>& sendData,                                    \
+            /*! [out] The non-zero value received from each rank */           \
+            UList<Native>& recvData,                                          \
+            /*! Message tag for the communication */                          \
+            const int tag,                                                    \
+            const label communicator = worldComm                              \
+        );                                                                    \
+                                                                              \
+        /*!\brief Exchange \c Native data between ranks [NBX]              */ \
+        /*! \p recvData map is always cleared initially so a simple check  */ \
+        /*! of its keys is sufficient to determine connectivity.           */ \
+        /*! \em non-parallel : copy own rank (if it exists)                */ \
+        /*! See notes about message tags and "nbx.tuning" opt switch       */ \
+        static void allToAllConsensus                                         \
+        (                                                                     \
+            /*! [in] The value at [proci] is sent to proci. */                \
+            const Map<Native>& sendData,                                      \
+            /*! [out] The values received from given ranks. */                \
+            Map<Native>& recvData,                                            \
+            /*! Message tag for the communication */                          \
+            const int tag,                                                    \
+            const label communicator = worldComm                              \
+        );                                                                    \
+                                                                              \
+        /*!\brief Exchange \c Native data between ranks [NBX]              */ \
+        /*! \returns any received data as a Map                            */ \
+        static Map<Native> allToAllConsensus                                  \
+        (                                                                     \
+            /*! [in] The value at [proci] is sent to proci. */                \
+            const Map<Native>& sendData,                                      \
+            /*! Message tag for the communication */                          \
+            const int tag,                                                    \
+            const label communicator = worldComm                              \
+        )                                                                     \
+        {                                                                     \
+            Map<Native> recvData;                                             \
+            allToAllConsensus(sendData, recvData, tag, communicator);         \
+            return recvData;                                                  \
+        }
 
-        //- Exchange \b non-zero integer data with all ranks in the communicator
+        Pstream_CommonRoutines(int32_t);
-        //- using non-blocking consensus exchange.
+        Pstream_CommonRoutines(int64_t);
-        //  The \c sendData[proci] is the (non-zero) value to send to proci.
-        //  After return recvData contains the non-zero values sent from the
-        //  other processors. The recvData list is always assigned zero before
-        //  receipt and values of zero are never transmitted.
-        //  After return recvData contains the data from the other processors.
-        //  \n
-        //  For \b non-parallel : does a simple copy of sendData to recvData
-        //
-        //  \note The message tag should be chosen to be a unique value
-        //  since the implementation uses probing with ANY_SOURCE !!
-        //  An initial barrier may help to avoid synchronisation problems
-        //  caused elsewhere (See "nbx.tuning" opt switch)
-        static void allToAllConsensus
-        (
-            const UList<int32_t>& sendData,
-            UList<int32_t>& recvData,
-            const int tag,
-            const label communicator = worldComm
-        );
 
-        //- Exchange \b non-zero integer data with all ranks in the communicator
+        #undef Pstream_CommonRoutines
-        //- using non-blocking consensus exchange.
-        //  The \c sendData[proci] is the (non-zero) value to send to proci.
-        //  After return recvData contains the non-zero values sent from the
-        //  other processors. The recvData list is always assigned zero before
-        //  receipt and values of zero are never transmitted.
-        //  After return recvData contains the data from the other processors.
-        //  \n
-        //  For \b non-parallel : does a simple copy of sendData to recvData
-        //
-        //  \note The message tag should be chosen to be a unique value
-        //  since the implementation uses probing with ANY_SOURCE !!
-        //  An initial barrier may help to avoid synchronisation problems
-        //  caused elsewhere (See "nbx.tuning" opt switch)
-        static void allToAllConsensus
-        (
-            const UList<int64_t>& sendData,
-            UList<int64_t>& recvData,
-            const int tag,
-            const label communicator = worldComm
-        );
-
-        //- Exchange \b non-zero integer data with all ranks in the communicator
-        //- using non-blocking consensus exchange.
-        //  The \c sendData[proci] is the (non-zero) value to send to proci.
-        //  After return recvData contains the non-zero values sent from the
-        //  other processors. Since the recvData map always cleared before
-        //  receipt and values of zero are never transmitted, a simple check
-        //  of its keys is sufficient to determine connectivity.
-        //  \n
-        //  For \b non-parallel : copy own rank (if it exists and non-zero)
-        //  from sendData to recvData.
-        //
-        //  \note The message tag should be chosen to be a unique value
-        //  since the implementation uses probing with ANY_SOURCE !!
-        //  An initial barrier may help to avoid synchronisation problems
-        //  caused elsewhere (See "nbx.tuning" opt switch)
-        static void allToAllConsensus
-        (
-            const Map<int32_t>& sendData,
-            Map<int32_t>& recvData,
-            const int tag,
-            const label communicator = worldComm
-        );
-
-        //- Exchange \b non-zero integer data with all ranks in the communicator
-        //- using non-blocking consensus exchange.
-        //  The \c sendData[proci] is the (non-zero) value to send to proci.
-        //  After return recvData contains the non-zero values sent from the
-        //  other processors. Since the recvData map always cleared before
-        //  receipt and values of zero are never transmitted, a simple check
-        //  of its keys is sufficient to determine connectivity.
-        //  \n
-        //  For \b non-parallel : copy own rank (if it exists and non-zero)
-        //  from sendData to recvData.
-        //
-        //  \note The message tag should be chosen to be a unique value
-        //  since the implementation uses probing with ANY_SOURCE !!
-        //  An initial barrier may help to avoid synchronisation problems
-        //  caused elsewhere (See "nbx.tuning" opt switch)
-        static void allToAllConsensus
-        (
-            const Map<int64_t>& sendData,
-            Map<int64_t>& recvData,
-            const int tag,
-            const label communicator = worldComm
-        );
 
 
     // Low-level gather/scatter routines
@@ -1121,13 +1076,7 @@ public:
             /*! Number of send/recv data per rank. Globally consistent! */    \
             int count,                                                        \
             const label communicator = worldComm                              \
-        );
+        );                                                                    \
-
-        Pstream_CommonRoutines(char);
-
-
-        #undef  Pstream_CommonRoutines
-        #define Pstream_CommonRoutines(Native)                                \
                                                                               \
         /*! \brief Receive variable length \c Native data from all ranks */   \
         static void gather                                                    \

src/Pstream/dummy/UPstreamGatherScatter.C

@@ -63,17 +63,9 @@ void Foam::UPstream::mpiAllGather                                             \
     int count,                                                                \
     const label comm                                                          \
 )                                                                             \
-{}
+{}                                                                            \
-
+                                                                              \
-Pstream_CommonRoutines(char);
+                                                                              \
-
-#undef Pstream_CommonRoutines
-
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-#undef  Pstream_CommonRoutines
-#define Pstream_CommonRoutines(Native)                                        \
 void Foam::UPstream::gather                                                   \
 (                                                                             \
     const Native* sendData,                                                   \

src/Pstream/mpi/UPstreamGatherScatter.C

@@ -79,17 +79,8 @@ void Foam::UPstream::mpiAllGather                                             \
         allData, count,                                                       \
         TaggedType, comm                                                      \
     );                                                                        \
-}
+}                                                                             \
-
+                                                                              \
-Pstream_CommonRoutines(char, MPI_BYTE);
-
-#undef Pstream_CommonRoutines
-
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-#undef  Pstream_CommonRoutines
-#define Pstream_CommonRoutines(Native, TaggedType)                            \
 void Foam::UPstream::gather                                                   \
 (                                                                             \
     const Native* sendData,                                                   \

src/Pstream/mpi/UPstreamWrapping.txx

@@ -507,7 +507,7 @@ void Foam::PstreamDetail::allToAllConsensus
 
     if (!UPstream::is_rank(comm))
     {
-        return;
+        return;  // Process not in communicator
     }
 
     const label myProci = UPstream::myProcNo(comm);
@@ -539,11 +539,15 @@ void Foam::PstreamDetail::allToAllConsensus
 
     if (!UPstream::is_parallel(comm))
     {
-        // deep copy
+        // Non-parallel : deep copy
         recvData.deepCopy(sendData);
         return;
     }
 
+    // Fake send/recv for myself
+    {
+        recvData[myProci] = sendData[myProci];
+    }
 
     // Implementation description
     // --------------------------
@@ -562,7 +566,10 @@ void Foam::PstreamDetail::allToAllConsensus
     // This is because we are dealing with a flat list of entries to
     // send and not a sparse Map etc.
 
-    DynamicList<MPI_Request> sendRequests(sendData.size());
+
+    // ------------------------------------------------------------------------
+    // Setup sends
+    // ------------------------------------------------------------------------
 
     profilingPstream::beginTiming();
 
@@ -573,20 +580,16 @@ void Foam::PstreamDetail::allToAllConsensus
         MPI_Barrier(PstreamGlobals::MPICommunicators_[comm]);
     }
 
+    DynamicList<MPI_Request> sendRequests(sendData.size());
 
-    // Start nonblocking synchronous send to process dest
+    // Start nonblocking synchronous send to destination rank
     for (label proci = 0; proci < numProc; ++proci)
     {
         if (sendData[proci] == zeroValue)
         {
             // Do not send/recv empty data
         }
-        else if (proci == myProci)
+        else if (proci != myProci)
-        {
-            // Do myself
-            recvData[proci] = sendData[proci];
-        }
-        else
         {
             // Has data to send
 
@@ -604,7 +607,9 @@ void Foam::PstreamDetail::allToAllConsensus
     }
 
 
+    // ------------------------------------------------------------------------
     // Probe and receive
+    // ------------------------------------------------------------------------
 
     MPI_Request barrierRequest;
 
@@ -721,22 +726,29 @@ void Foam::PstreamDetail::allToAllConsensus
     }
 
     // Initial: clear out everything
-    const Type zeroValue = pTraits<Type>::zero;
     recvBufs.clear();
 
-    if (!UPstream::is_parallel(comm))
+    // Fake send/recv for myself - parallel or non-parallel
     {
-        // Do myself
         const auto iter = sendBufs.find(myProci);
-        if (iter.good() && (iter.val() != zeroValue))
+        if (iter.good())
         {
             // Do myself: insert_or_assign
             recvBufs(iter.key()) = iter.val();
         }
+    }
+
+    if (!UPstream::is_parallel(comm))
+    {
+        // Nothing left to do
         return;
     }
 
 
+    // ------------------------------------------------------------------------
+    // Setup sends
+    // ------------------------------------------------------------------------
+
     // Algorithm NBX: Nonblocking consensus
     // Implementation like above, but sending map data.
 
@@ -752,7 +764,7 @@ void Foam::PstreamDetail::allToAllConsensus
     }
 
 
-    // Start nonblocking synchronous send to process dest
+    // Start nonblocking synchronous send to destination ranks
 
     // Same as forAllConstIters()
     const auto endIter = sendBufs.cend();
@@ -761,19 +773,8 @@ void Foam::PstreamDetail::allToAllConsensus
         const label proci = iter.key();
         const auto& sendData = iter.val();
 
-        if (sendData == zeroValue)
+        if (proci != myProci && proci >= 0 && proci < numProc)
         {
-            // Do not send/recv empty/zero data
-        }
-        else if (proci == myProci)
-        {
-            // Do myself: insert_or_assign
-            recvBufs(proci) = sendData;
-        }
-        else
-        {
-            // Has data to send
-
             MPI_Issend
             (
                &sendData,
@@ -788,7 +789,9 @@ void Foam::PstreamDetail::allToAllConsensus
     }
 
 
+    // ------------------------------------------------------------------------
     // Probe and receive
+    // ------------------------------------------------------------------------
 
     MPI_Request barrierRequest;