diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index 42ac1d774b..81e4d599f1 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -266,14 +266,14 @@ StringStreams = $(Streams)/StringStreams
 $(StringStreams)/StringStream.C
 
 Pstreams = $(Streams)/Pstreams
-$(Pstreams)/UIPstream.C
-$(Pstreams)/IPstream.C
-/* $(Pstreams)/UPstream.C in global.Cver */
+/* $(Pstreams)/UPstream.C in global.C */
 $(Pstreams)/UPstreamCommsStruct.C
 $(Pstreams)/Pstream.C
-$(Pstreams)/UOPstream.C
-$(Pstreams)/OPstream.C
 $(Pstreams)/PstreamBuffers.C
+$(Pstreams)/UIPstreamBase.C
+$(Pstreams)/UOPstreamBase.C
+$(Pstreams)/IPstreams.C
+$(Pstreams)/OPstreams.C
 
 dictionary = db/dictionary
 $(dictionary)/dictionary.C
diff --git a/src/Pstream/dummy/UIPread.C b/src/OpenFOAM/db/IOstreams/Pstreams/IPstreams.C
similarity index 57%
rename from src/Pstream/dummy/UIPread.C
rename to src/OpenFOAM/db/IOstreams/Pstreams/IPstreams.C
index f6cc67da04..232a8d0754 100644
--- a/src/Pstream/dummy/UIPread.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/IPstreams.C
@@ -5,8 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2011-2015 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -24,12 +23,11 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-Description
-    Read from UIPstream
-
 \*---------------------------------------------------------------------------*/
 
 #include "UIPstream.H"
+#include "IPstream.H"
+#include "IOstreams.H"
 
 // * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
 
@@ -45,51 +43,78 @@ Foam::UIPstream::UIPstream
     IOstreamOption::streamFormat fmt
 )
 :
-    UPstream(commsType),
-    Istream(fmt, IOstreamOption::currentVersion),
-    fromProcNo_(fromProcNo),
-    recvBuf_(receiveBuf),
-    recvBufPos_(receiveBufPosition),
-    tag_(tag),
-    comm_(comm),
-    clearAtEnd_(clearAtEnd),
-    messageSize_(0)
+    UIPstreamBase
+    (
+        commsType,
+        fromProcNo,
+        receiveBuf,
+        receiveBufPosition,
+        tag,
+        comm,
+        clearAtEnd,
+        fmt
+    )
 {
-    NotImplemented;
+    if (commsType == commsTypes::nonBlocking)
+    {
+        // Message is already received into buffer
+    }
+    else
+    {
+        bufferIPCrecv();
+    }
 }
 
 
 Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
 :
-    UPstream(buffers.commsType_),
-    Istream(buffers.format_, IOstreamOption::currentVersion),
-    fromProcNo_(fromProcNo),
-    recvBuf_(buffers.recvBuf_[fromProcNo]),
-    recvBufPos_(buffers.recvBufPos_[fromProcNo]),
-    tag_(buffers.tag_),
-    comm_(buffers.comm_),
-    clearAtEnd_(true),
-    messageSize_(0)
+    UIPstreamBase(fromProcNo, buffers)
 {
-    NotImplemented;
+    if (commsType() == commsTypes::nonBlocking)
+    {
+        // Message is already received into buffer
+        messageSize_ = recvBuf_.size();
+
+        if (debug)
+        {
+            Pout<< "UIPstream::UIPstream PstreamBuffers :"
+                << " fromProcNo:" << fromProcNo_
+                << " tag:" << tag_ << " comm:" << comm_
+                << " receive buffer size:" << messageSize_
+                << Foam::endl;
+        }
+    }
+    else
+    {
+        bufferIPCrecv();
+    }
 }
 
 
-// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
-
-Foam::label Foam::UIPstream::read
+Foam::IPstream::IPstream
 (
     const commsTypes commsType,
     const int fromProcNo,
-    char* buf,
-    const std::streamsize bufSize,
+    const label bufSize,
     const int tag,
-    const label communicator
+    const label comm,
+    IOstreamOption::streamFormat fmt
 )
-{
-    NotImplemented;
-    return 0;
-}
+:
+    Pstream(commsType, bufSize),
+    UIPstream
+    (
+        commsType,
+        fromProcNo,
+        Pstream::transferBuf_,
+        transferBufPosition_,
+        tag,
+        comm,
+        false,  // Do not clear Pstream::transferBuf_ if at end
+        fmt
+    ),
+    transferBufPosition_(0)
+{}
 
 
 // ************************************************************************* //
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/IPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
similarity index 60%
rename from src/OpenFOAM/db/IOstreams/Pstreams/IPstream.C
rename to src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
index af8035eea7..70e557ab3f 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/IPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
@@ -5,8 +5,8 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2011-2013 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2011 OpenFOAM Foundation
+    Copyright (C) 2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -26,14 +26,36 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-#include "IPstream.H"
+#include "UOPstream.H"
+#include "OPstream.H"
 
 // * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
 
-Foam::IPstream::IPstream
+Foam::UOPstream::UOPstream
 (
     const commsTypes commsType,
-    const int fromProcNo,
+    const int toProcNo,
+    DynamicList<char>& sendBuf,
+    const int tag,
+    const label comm,
+    const bool sendAtDestruct,
+    IOstreamOption::streamFormat fmt
+)
+:
+    UOPstreamBase(commsType, toProcNo, sendBuf, tag, comm, sendAtDestruct, fmt)
+{}
+
+
+Foam::UOPstream::UOPstream(const int toProcNo, PstreamBuffers& buffers)
+:
+    UOPstreamBase(toProcNo, buffers)
+{}
+
+
+Foam::OPstream::OPstream
+(
+    const commsTypes commsType,
+    const int toProcNo,
     const label bufSize,
     const int tag,
     const label comm,
@@ -41,19 +63,34 @@ Foam::IPstream::IPstream
 )
 :
     Pstream(commsType, bufSize),
-    UIPstream
+    UOPstream
     (
         commsType,
-        fromProcNo,
+        toProcNo,
         Pstream::transferBuf_,
-        transferBufPosition_,
         tag,
         comm,
-        false,  // Do not clear Pstream::transferBuf_ if at end
+        true,  // sendAtDestruct
         fmt
-    ),
-    transferBufPosition_(0)
+    )
 {}
 
 
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+Foam::UOPstream::~UOPstream()
+{
+    if (sendAtDestruct_)
+    {
+        if (!bufferIPCsend())
+        {
+            FatalErrorInFunction
+                << "Failed sending outgoing message of size "
+                << sendBuf_.size() << " to processor " << toProcNo_
+                << Foam::abort(FatalError);
+        }
+    }
+}
+
+
 // ************************************************************************* //
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
index 2607ce97ab..85dc6fad6e 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -28,6 +28,35 @@ License
 
 #include "PstreamBuffers.H"
 
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+void Foam::PstreamBuffers::finalExchange
+(
+    labelList& recvSizes,
+    const bool block
+)
+{
+    // Could also check that it is not called twice
+    finishedSendsCalled_ = true;
+
+    if (commsType_ == UPstream::commsTypes::nonBlocking)
+    {
+        // all-to-all
+        Pstream::exchangeSizes(sendBuf_, recvSizes, comm_);
+
+        Pstream::exchange<DynamicList<char>, char>
+        (
+            sendBuf_,
+            recvSizes,
+            recvBuf_,
+            tag_,
+            comm_,
+            block
+        );
+    }
+}
+
+
 // * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
 
 Foam::PstreamBuffers::PstreamBuffers
@@ -38,14 +67,14 @@ Foam::PstreamBuffers::PstreamBuffers
     IOstreamOption::streamFormat fmt
 )
 :
+    finishedSendsCalled_(false),
+    format_(fmt),
     commsType_(commsType),
     tag_(tag),
     comm_(comm),
-    format_(fmt),
     sendBuf_(UPstream::nProcs(comm)),
     recvBuf_(UPstream::nProcs(comm)),
-    recvBufPos_(UPstream::nProcs(comm), Zero),
-    finishedSendsCalled_(false)
+    recvBufPos_(UPstream::nProcs(comm), Zero)
 {}
 
 
@@ -70,45 +99,38 @@ Foam::PstreamBuffers::~PstreamBuffers()
 
 // * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
-void Foam::PstreamBuffers::finishedSends(const bool block)
+void Foam::PstreamBuffers::clear()
 {
-    // Could also check that it is not called twice
-    finishedSendsCalled_ = true;
-
-    if (commsType_ == UPstream::commsTypes::nonBlocking)
+    for (DynamicList<char>& buf : sendBuf_)
     {
-        Pstream::exchange<DynamicList<char>, char>
-        (
-            sendBuf_,
-            recvBuf_,
-            tag_,
-            comm_,
-            block
-        );
+        buf.clear();
     }
+    for (DynamicList<char>& buf : recvBuf_)
+    {
+        buf.clear();
+    }
+    recvBufPos_ = 0;
+
+    finishedSendsCalled_ = false;
 }
 
 
-void Foam::PstreamBuffers::finishedSends(labelList& recvSizes, const bool block)
+void Foam::PstreamBuffers::finishedSends(const bool block)
 {
-    // Could also check that it is not called twice
-    finishedSendsCalled_ = true;
+    labelList recvSizes;
+    finalExchange(recvSizes, block);
+}
 
-    if (commsType_ == UPstream::commsTypes::nonBlocking)
-    {
-        Pstream::exchangeSizes(sendBuf_, recvSizes, comm_);
 
-        Pstream::exchange<DynamicList<char>, char>
-        (
-            sendBuf_,
-            recvSizes,
-            recvBuf_,
-            tag_,
-            comm_,
-            block
-        );
-    }
-    else
+void Foam::PstreamBuffers::finishedSends
+(
+    labelList& recvSizes,
+    const bool block
+)
+{
+    finalExchange(recvSizes, block);
+
+    if (commsType_ != UPstream::commsTypes::nonBlocking)
     {
         FatalErrorInFunction
             << "Obtaining sizes not supported in "
@@ -122,19 +144,4 @@ void Foam::PstreamBuffers::finishedSends(labelList& recvSizes, const bool block)
 }
 
 
-void Foam::PstreamBuffers::clear()
-{
-    for (DynamicList<char>& buf : sendBuf_)
-    {
-        buf.clear();
-    }
-    for (DynamicList<char>& buf : recvBuf_)
-    {
-        buf.clear();
-    }
-    recvBufPos_ = 0;
-    finishedSendsCalled_ = false;
-}
-
-
 // ************************************************************************* //
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
index de7414f469..5f178e000e 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -70,8 +70,8 @@ SourceFiles
 
 #include "Pstream.H"
 
-#ifndef PstreamBuffers_H
-#define PstreamBuffers_H
+#ifndef Foam_PstreamBuffers_H
+#define Foam_PstreamBuffers_H
 
 #include "DynamicList.H"
 #include "UPstream.H"
@@ -83,16 +83,24 @@ namespace Foam
 {
 
 /*---------------------------------------------------------------------------*\
-                          Class PstreamBuffers Declaration
+                       Class PstreamBuffers Declaration
 \*---------------------------------------------------------------------------*/
 
 class PstreamBuffers
 {
-    friend class UOPstream;
-    friend class UIPstream;
+    // Friendship
+    friend class UOPstreamBase;  // Access to sendBuf_
+    friend class UIPstreamBase;  // Access to recvBuf_ recvBufPos_;
+
 
     // Private Data
 
+        //- Track if sends are complete
+        bool finishedSendsCalled_;
+
+        //- Buffer format (ascii | binary)
+        const IOstreamOption::streamFormat format_;
+
         //- Communications type of this stream
         const UPstream::commsTypes commsType_;
 
@@ -102,9 +110,6 @@ class PstreamBuffers
         //- Communicator
         const label comm_;
 
-        //- Buffer format (ascii | binary)
-        const IOstreamOption::streamFormat format_;
-
         //- Send buffer
         List<DynamicList<char>> sendBuf_;
 
@@ -114,8 +119,12 @@ class PstreamBuffers
         //- Current read positions within recvBuf_
         labelList recvBufPos_;
 
-        //- Track if sends are complete
-        bool finishedSendsCalled_;
+
+    // Private Member Functions
+
+        //- Mark all sends as having been done.
+        //  This will start receives in non-blocking mode.
+        void finalExchange(labelList& recvSizes, const bool block);
 
 
 public:
@@ -138,6 +147,20 @@ public:
 
     // Member Functions
 
+    // Access
+
+        //- The associated buffer format (ascii | binary)
+        IOstreamOption::streamFormat format() const noexcept
+        {
+            return format_;
+        }
+
+        //- The communications type of the stream
+        UPstream::commsTypes commsType() const noexcept
+        {
+            return commsType_;
+        }
+
         //- The transfer message type
         int tag() const noexcept
         {
@@ -150,6 +173,22 @@ public:
             return comm_;
         }
 
+        //- True if finishedSends has been called
+        bool finished() const noexcept
+        {
+            return finishedSendsCalled_;
+        }
+
+
+    // Edit
+
+        //- Reset (clear) individual buffers and reset state.
+        //  Does not clear buffer storage
+        void clear();
+
+
+    // Functions
+
         //- Mark all sends as having been done.
         //  This will start receives in non-blocking mode.
         //  If block will wait for all transfers to finish
@@ -160,10 +199,6 @@ public:
         //  Same as above but also returns sizes (bytes) received.
         //  \note currently only valid for non-blocking.
         void finishedSends(labelList& recvSizes, const bool block = true);
-
-        //- Reset (clear) individual buffers and reset state.
-        //  Does not clear buffer storage
-        void clear();
 };
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H
index 7b44640fc8..5e593c93eb 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2013 OpenFOAM Foundation
-    Copyright (C) 2017-2021 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -25,24 +25,26 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Class
-    Foam::UIPstream
+    Foam::UIPstreamBase
 
 Description
-    Input inter-processor communications stream operating on external
-    buffer.
+    Base class for input inter-processor communications stream
+    (ie, parallel streams).
+    Not to be used directly, thus contructors are protected.
 
 SourceFiles
-    UIPstream.C
+    UIPstreamBase.C
 
 \*---------------------------------------------------------------------------*/
 
 #include "Pstream.H"
 
-#ifndef UIPstream_H
-#define UIPstream_H
+#ifndef Foam_UIPstream_H
+#define Foam_UIPstream_H
 
 #include "UPstream.H"
 #include "Istream.H"
+#include "DynamicList.H"
 #include "PstreamBuffers.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -51,31 +53,14 @@ namespace Foam
 {
 
 /*---------------------------------------------------------------------------*\
-                           Class UIPstream Declaration
+                        Class UIPstreamBase Declaration
 \*---------------------------------------------------------------------------*/
 
-class UIPstream
+class UIPstreamBase
 :
     public UPstream,
     public Istream
 {
-    // Private Data
-
-        int fromProcNo_;
-
-        DynamicList<char>& recvBuf_;
-
-        label& recvBufPos_;
-
-        const int tag_;
-
-        const label comm_;
-
-        const bool clearAtEnd_;
-
-        int messageSize_;
-
-
     // Private Member Functions
 
         //- Check buffer position against messageSize_ for EOF
@@ -96,14 +81,31 @@ class UIPstream
         inline Istream& readString(std::string& str);
 
 
-public:
+protected:
 
-    // Constructors
+    // Protected Data
+
+        int fromProcNo_;
+
+        DynamicList<char>& recvBuf_;
+
+        label& recvBufPos_;
+
+        const int tag_;
+
+        const label comm_;
+
+        const bool clearAtEnd_;
+
+        int messageSize_;
+
+
+    // Protected Constructors
 
         //- Construct given process index to read from using the given
         //- attached receive buffer, optional communication characteristics
         //- and IO format
-        UIPstream
+        UIPstreamBase
         (
             const commsTypes commsType,
             const int fromProcNo,
@@ -116,11 +118,14 @@ public:
         );
 
         //- Construct given buffers
-        UIPstream(const int fromProcNo, PstreamBuffers& buffers);
+        UIPstreamBase(const int fromProcNo, PstreamBuffers& buffers);
 
 
-    //- Destructor
-    ~UIPstream();
+public:
+
+
+    //- Destructor. Optionally clears external receive buffer.
+    virtual ~UIPstreamBase();
 
 
     // Member Functions
@@ -128,7 +133,7 @@ public:
         // Inquiry
 
             //- Return flags of output stream
-            ios_base::fmtflags flags() const
+            virtual ios_base::fmtflags flags() const
             {
                 return ios_base::fmtflags(0);
             }
@@ -136,18 +141,6 @@ public:
 
         // Read Functions
 
-            //- Read into given buffer from given processor
-            //  \return the message size
-            static label read
-            (
-                const commsTypes commsType,
-                const int fromProcNo,
-                char* buf,
-                const std::streamsize bufSize,
-                const int tag = UPstream::msgType(),
-                const label communicator = UPstream::worldComm
-            );
-
             //- Return next token from stream
             Istream& read(token& t);
 
@@ -191,7 +184,7 @@ public:
         // Edit
 
             //- Set flags of stream
-            ios_base::fmtflags flags(const ios_base::fmtflags)
+            virtual ios_base::fmtflags flags(const ios_base::fmtflags)
             {
                 return ios_base::fmtflags(0);
             }
@@ -204,6 +197,71 @@ public:
 };
 
 
+/*---------------------------------------------------------------------------*\
+                           Class UIPstream Declaration
+\*---------------------------------------------------------------------------*/
+
+//- Input inter-processor communications stream
+//- using MPI send/recv etc. - operating on external buffer.
+class UIPstream
+:
+    public UIPstreamBase
+{
+    // Private Member Functions
+
+        //- Initial buffer recv, called by constructor (blocking | scheduled)
+        void bufferIPCrecv();
+
+
+public:
+
+    // Constructors
+
+        //- Construct given process index to read from using the given
+        //- attached receive buffer, optional communication characteristics
+        //- and IO format
+        UIPstream
+        (
+            const commsTypes commsType,
+            const int fromProcNo,
+            DynamicList<char>& receiveBuf,
+            label& receiveBufPosition,
+            const int tag = UPstream::msgType(),
+            const label comm = UPstream::worldComm,
+            const bool clearAtEnd = false,   // destroy receiveBuf if at end
+            IOstreamOption::streamFormat fmt = IOstreamOption::BINARY
+        );
+
+        //- Construct given buffers
+        UIPstream(const int fromProcNo, PstreamBuffers& buffers);
+
+
+    //- Destructor
+    virtual ~UIPstream() = default;
+
+
+    // Member Functions
+
+        //- Use all read methods from base
+        using UIPstreamBase::read;
+
+
+    // Static Functions
+
+        //- Read buffer contents from given processor
+        //  \return the message size
+        static label read
+        (
+            const commsTypes commsType,
+            const int fromProcNo,
+            char* buf,
+            const std::streamsize bufSize,
+            const int tag = UPstream::msgType(),
+            const label comm = UPstream::worldComm
+        );
+};
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
similarity index 77%
rename from src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.C
rename to src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
index 5d8187da08..4a6108788b 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
@@ -74,7 +74,7 @@ inline static label byteAlign(const label pos, const size_t align)
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
-inline void Foam::UIPstream::checkEof()
+inline void Foam::UIPstreamBase::checkEof()
 {
     if (recvBufPos_ == messageSize_)
     {
@@ -83,14 +83,14 @@ inline void Foam::UIPstream::checkEof()
 }
 
 
-inline void Foam::UIPstream::prepareBuffer(const size_t align)
+inline void Foam::UIPstreamBase::prepareBuffer(const size_t align)
 {
     recvBufPos_ = byteAlign(recvBufPos_, align);
 }
 
 
 template<class T>
-inline void Foam::UIPstream::readFromBuffer(T& val)
+inline void Foam::UIPstreamBase::readFromBuffer(T& val)
 {
     prepareBuffer(sizeof(T));
 
@@ -100,7 +100,7 @@ inline void Foam::UIPstream::readFromBuffer(T& val)
 }
 
 
-inline void Foam::UIPstream::readFromBuffer
+inline void Foam::UIPstreamBase::readFromBuffer
 (
     void* data,
     const size_t count
@@ -119,7 +119,7 @@ inline void Foam::UIPstream::readFromBuffer
 }
 
 
-inline Foam::Istream& Foam::UIPstream::readString(std::string& str)
+inline Foam::Istream& Foam::UIPstreamBase::readString(std::string& str)
 {
     // Use std::string::assign() to copy content, including '\0'.
     // Stripping (when desired) is the responsibility of the sending side.
@@ -142,15 +142,78 @@ inline Foam::Istream& Foam::UIPstream::readString(std::string& str)
 }
 
 
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::UIPstreamBase::UIPstreamBase
+(
+    const commsTypes commsType,
+    const int fromProcNo,
+    DynamicList<char>& receiveBuf,
+    label& receiveBufPosition,
+    const int tag,
+    const label comm,
+    const bool clearAtEnd,
+    IOstreamOption::streamFormat fmt
+)
+:
+    UPstream(commsType),
+    Istream(fmt, IOstreamOption::currentVersion),
+    fromProcNo_(fromProcNo),
+    recvBuf_(receiveBuf),
+    recvBufPos_(receiveBufPosition),
+    tag_(tag),
+    comm_(comm),
+    clearAtEnd_(clearAtEnd),
+    messageSize_(0)
+{
+    setOpened();
+    setGood();
+}
+
+
+Foam::UIPstreamBase::UIPstreamBase
+(
+    const int fromProcNo,
+    PstreamBuffers& buffers
+)
+:
+    UPstream(buffers.commsType()),
+    Istream(buffers.format(), IOstreamOption::currentVersion),
+    fromProcNo_(fromProcNo),
+    recvBuf_(buffers.recvBuf_[fromProcNo]),
+    recvBufPos_(buffers.recvBufPos_[fromProcNo]),
+    tag_(buffers.tag()),
+    comm_(buffers.comm()),
+    clearAtEnd_(true),
+    messageSize_(0)
+{
+    if
+    (
+        commsType() != UPstream::commsTypes::scheduled
+     && !buffers.finished()
+    )
+    {
+        FatalErrorInFunction
+            << "PstreamBuffers::finishedSends() never called." << endl
+            << "Please call PstreamBuffers::finishedSends() after doing"
+            << " all your sends (using UOPstream) and before doing any"
+            << " receives (using UIPstream)" << Foam::exit(FatalError);
+    }
+
+    setOpened();
+    setGood();
+}
+
+
 // * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
 
-Foam::UIPstream::~UIPstream()
+Foam::UIPstreamBase::~UIPstreamBase()
 {
     if (clearAtEnd_ && eof())
     {
         if (debug)
         {
-            Pout<< "UIPstream::~UIPstream() : tag:" << tag_
+            Pout<< "UIPstreamBase Destructor : tag:" << tag_
                 << " fromProcNo:" << fromProcNo_
                 << " clearing receive buffer of size "
                 << recvBuf_.size()
@@ -163,7 +226,7 @@ Foam::UIPstream::~UIPstream()
 
 // * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
-Foam::Istream& Foam::UIPstream::read(token& t)
+Foam::Istream& Foam::UIPstreamBase::read(token& t)
 {
     // Return the put back token if it exists
     // - with additional handling for special stream flags
@@ -341,7 +404,7 @@ Foam::Istream& Foam::UIPstream::read(token& t)
 }
 
 
-Foam::Istream& Foam::UIPstream::read(char& c)
+Foam::Istream& Foam::UIPstreamBase::read(char& c)
 {
     c = recvBuf_[recvBufPos_];
     ++recvBufPos_;
@@ -350,40 +413,40 @@ Foam::Istream& Foam::UIPstream::read(char& c)
 }
 
 
-Foam::Istream& Foam::UIPstream::read(word& str)
+Foam::Istream& Foam::UIPstreamBase::read(word& str)
 {
     return readString(str);
 }
 
 
-Foam::Istream& Foam::UIPstream::read(string& str)
+Foam::Istream& Foam::UIPstreamBase::read(string& str)
 {
     return readString(str);
 }
 
 
-Foam::Istream& Foam::UIPstream::read(label& val)
+Foam::Istream& Foam::UIPstreamBase::read(label& val)
 {
     readFromBuffer(val);
     return *this;
 }
 
 
-Foam::Istream& Foam::UIPstream::read(floatScalar& val)
+Foam::Istream& Foam::UIPstreamBase::read(floatScalar& val)
 {
     readFromBuffer(val);
     return *this;
 }
 
 
-Foam::Istream& Foam::UIPstream::read(doubleScalar& val)
+Foam::Istream& Foam::UIPstreamBase::read(doubleScalar& val)
 {
     readFromBuffer(val);
     return *this;
 }
 
 
-Foam::Istream& Foam::UIPstream::read(char* data, std::streamsize count)
+Foam::Istream& Foam::UIPstreamBase::read(char* data, std::streamsize count)
 {
     if (count)
     {
@@ -398,7 +461,7 @@ Foam::Istream& Foam::UIPstream::read(char* data, std::streamsize count)
 }
 
 
-Foam::Istream& Foam::UIPstream::readRaw(char* data, std::streamsize count)
+Foam::Istream& Foam::UIPstreamBase::readRaw(char* data, std::streamsize count)
 {
     // No check for format() == BINARY since this is either done in the
     // beginRawRead() method, or the caller knows what they are doing.
@@ -409,7 +472,7 @@ Foam::Istream& Foam::UIPstream::readRaw(char* data, std::streamsize count)
 }
 
 
-bool Foam::UIPstream::beginRawRead()
+bool Foam::UIPstreamBase::beginRawRead()
 {
     if (format() != BINARY)
     {
@@ -427,13 +490,13 @@ bool Foam::UIPstream::beginRawRead()
 }
 
 
-void Foam::UIPstream::rewind()
+void Foam::UIPstreamBase::rewind()
 {
     recvBufPos_ = 0;
 }
 
 
-void Foam::UIPstream::print(Ostream& os) const
+void Foam::UIPstreamBase::print(Ostream& os) const
 {
     os  << "Reading from processor " << fromProcNo_
         << " using communicator " << comm_
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.H
index d4eefe305e..da7365a2f9 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2014 OpenFOAM Foundation
-    Copyright (C) 2017-2021 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -25,21 +25,22 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Class
-    Foam::UOPstream
+    Foam::UOPstreamBase
 
 Description
-    Output inter-processor communications stream operating on external
-    buffer.
+    Base class for output inter-processor communications stream
+    (ie, parallel streams).
+    Not to be used directly, thus contructors are protected.
 
 SourceFiles
-    UOPstream.C
+    UOPstreamBase.C
 
 \*---------------------------------------------------------------------------*/
 
 #include "Pstream.H"
 
-#ifndef UOPstream_H
-#define UOPstream_H
+#ifndef Foam_UOPstream_H
+#define Foam_UOPstream_H
 
 #include "UPstream.H"
 #include "Ostream.H"
@@ -52,27 +53,14 @@ namespace Foam
 {
 
 /*---------------------------------------------------------------------------*\
-                          Class UOPstream Declaration
+                        Class UOPstreamBase Declaration
 \*---------------------------------------------------------------------------*/
 
-class UOPstream
+class UOPstreamBase
 :
     public UPstream,
     public Ostream
 {
-    // Private Data
-
-        int toProcNo_;
-
-        DynamicList<char>& sendBuf_;
-
-        const int tag_;
-
-        const label comm_;
-
-        const bool sendAtDestruct_;
-
-
     // Private Member Functions
 
         //- Prepare send buffer for count bytes of output,
@@ -100,14 +88,27 @@ class UOPstream
         inline void putString(const std::string& str);
 
 
-public:
+protected:
 
-    // Constructors
+    // Protected Data
+
+        int toProcNo_;
+
+        DynamicList<char>& sendBuf_;
+
+        const int tag_;
+
+        const label comm_;
+
+        const bool sendAtDestruct_;
+
+
+    // Protected Constructors
 
         //- Construct given process index to write to using the given
         //- attached send buffer, optional communication characteristics
         //- and IO format
-        UOPstream
+        UOPstreamBase
         (
             const commsTypes commsType,
             const int toProcNo,
@@ -119,11 +120,13 @@ public:
         );
 
         //- Construct given buffers
-        UOPstream(const int toProcNo, PstreamBuffers& buffers);
+        UOPstreamBase(const int toProcNo, PstreamBuffers& buffers);
 
 
+public:
+
     //- Destructor.
-    ~UOPstream();
+    virtual ~UOPstreamBase();
 
 
     // Member Functions
@@ -139,17 +142,6 @@ public:
 
         // Write Functions
 
-            //- Write given buffer to given processor
-            static bool write
-            (
-                const commsTypes commsType,
-                const int toProcNo,
-                const char* buf,
-                const std::streamsize bufSize,
-                const int tag = UPstream::msgType(),
-                const label communicator = UPstream::worldComm
-            );
-
             //- Write token to stream or otherwise handle it.
             //  \return false if the token type was not handled by this method
             virtual bool write(const token& tok);
@@ -262,7 +254,7 @@ public:
         // Edit
 
             //- Set flags of stream
-            ios_base::fmtflags flags(const ios_base::fmtflags)
+            virtual ios_base::fmtflags flags(const ios_base::fmtflags)
             {
                 return ios_base::fmtflags(0);
             }
@@ -275,6 +267,70 @@ public:
 };
 
 
+/*---------------------------------------------------------------------------*\
+                          Class UOPstream Declaration
+\*---------------------------------------------------------------------------*/
+
+//- Output inter-processor communications stream
+//- using MPI send/recv etc. - operating on external buffer.
+class UOPstream
+:
+    public UOPstreamBase
+{
+    // Private Member Functions
+
+        //- Final buffer send, called by destructor
+        bool bufferIPCsend();
+
+
+public:
+
+    // Constructors
+
+        //- Construct given process index to write to using the given
+        //- attached send buffer, optional communication characteristics
+        //- and IO format
+        UOPstream
+        (
+            const commsTypes commsType,
+            const int toProcNo,
+            DynamicList<char>& sendBuf,
+            const int tag = UPstream::msgType(),
+            const label comm = UPstream::worldComm,
+            const bool sendAtDestruct = true,
+            IOstreamOption::streamFormat fmt = IOstreamOption::BINARY
+        );
+
+        //- Construct given buffers
+        UOPstream(const int toProcNo, PstreamBuffers& buffers);
+
+
+    //- Destructor, usually sends buffer on destruct.
+    virtual ~UOPstream();
+
+
+    // Member Functions
+
+        //- Use all write methods from base class
+        using UOPstreamBase::write;
+
+
+    // Static Functions
+
+        //- Write buffer contents to given processor
+        //  \return True on success
+        static bool write
+        (
+            const commsTypes commsType,
+            const int toProcNo,
+            const char* buf,
+            const std::streamsize bufSize,
+            const int tag = UPstream::msgType(),
+            const label comm = UPstream::worldComm
+        );
+};
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
similarity index 77%
rename from src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C
rename to src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
index d65a2a5011..25992abec8 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,7 +52,7 @@ inline static label byteAlign(const label pos, const size_t align)
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
-inline void Foam::UOPstream::prepareBuffer
+inline void Foam::UOPstreamBase::prepareBuffer
 (
     const size_t count,
     const size_t align
@@ -75,13 +75,13 @@ inline void Foam::UOPstream::prepareBuffer
 
 
 template<class T>
-inline void Foam::UOPstream::writeToBuffer(const T& val)
+inline void Foam::UOPstreamBase::writeToBuffer(const T& val)
 {
     writeToBuffer(&val, sizeof(T), sizeof(T));
 }
 
 
-inline void Foam::UOPstream::writeToBuffer
+inline void Foam::UOPstreamBase::writeToBuffer
 (
     const void* data,
     const size_t count,
@@ -111,7 +111,7 @@ inline void Foam::UOPstream::writeToBuffer
 }
 
 
-inline void Foam::UOPstream::putChar(const char c)
+inline void Foam::UOPstreamBase::putChar(const char c)
 {
     if (!sendBuf_.capacity())
     {
@@ -121,7 +121,7 @@ inline void Foam::UOPstream::putChar(const char c)
 }
 
 
-inline void Foam::UOPstream::putString(const std::string& str)
+inline void Foam::UOPstreamBase::putString(const std::string& str)
 {
     const size_t len = str.size();
     writeToBuffer(len);
@@ -131,7 +131,7 @@ inline void Foam::UOPstream::putString(const std::string& str)
 
 // * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
 
-Foam::UOPstream::UOPstream
+Foam::UOPstreamBase::UOPstreamBase
 (
     const commsTypes commsType,
     const int toProcNo,
@@ -155,15 +155,15 @@ Foam::UOPstream::UOPstream
 }
 
 
-Foam::UOPstream::UOPstream(const int toProcNo, PstreamBuffers& buffers)
+Foam::UOPstreamBase::UOPstreamBase(const int toProcNo, PstreamBuffers& buffers)
 :
-    UPstream(buffers.commsType_),
-    Ostream(buffers.format_, IOstreamOption::currentVersion),
+    UPstream(buffers.commsType()),
+    Ostream(buffers.format(), IOstreamOption::currentVersion),
     toProcNo_(toProcNo),
     sendBuf_(buffers.sendBuf_[toProcNo]),
-    tag_(buffers.tag_),
-    comm_(buffers.comm_),
-    sendAtDestruct_(buffers.commsType_ != UPstream::commsTypes::nonBlocking)
+    tag_(buffers.tag()),
+    comm_(buffers.comm()),
+    sendAtDestruct_(buffers.commsType() != UPstream::commsTypes::nonBlocking)
 {
     setOpened();
     setGood();
@@ -172,35 +172,13 @@ Foam::UOPstream::UOPstream(const int toProcNo, PstreamBuffers& buffers)
 
 // * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
 
-Foam::UOPstream::~UOPstream()
-{
-    if (sendAtDestruct_)
-    {
-        if
-        (
-            !UOPstream::write
-            (
-                commsType_,
-                toProcNo_,
-                sendBuf_.cdata(),
-                sendBuf_.size(),
-                tag_,
-                comm_
-            )
-        )
-        {
-            FatalErrorInFunction
-                << "Failed sending outgoing message of size " << sendBuf_.size()
-                << " to processor " << toProcNo_
-                << Foam::abort(FatalError);
-        }
-    }
-}
+Foam::UOPstreamBase::~UOPstreamBase()
+{}
 
 
 // * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
-bool Foam::UOPstream::write(const token& tok)
+bool Foam::UOPstreamBase::write(const token& tok)
 {
     // Direct token handling only for some types
 
@@ -244,7 +222,7 @@ bool Foam::UOPstream::write(const token& tok)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const char c)
+Foam::Ostream& Foam::UOPstreamBase::write(const char c)
 {
     if (!isspace(c))
     {
@@ -255,7 +233,7 @@ Foam::Ostream& Foam::UOPstream::write(const char c)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const char* str)
+Foam::Ostream& Foam::UOPstreamBase::write(const char* str)
 {
     const word nonWhiteChars(string::validate<word>(str));
 
@@ -272,7 +250,7 @@ Foam::Ostream& Foam::UOPstream::write(const char* str)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const word& str)
+Foam::Ostream& Foam::UOPstreamBase::write(const word& str)
 {
     putChar(token::tokenType::WORD);
     putString(str);
@@ -281,7 +259,7 @@ Foam::Ostream& Foam::UOPstream::write(const word& str)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const string& str)
+Foam::Ostream& Foam::UOPstreamBase::write(const string& str)
 {
     putChar(token::tokenType::STRING);
     putString(str);
@@ -290,7 +268,7 @@ Foam::Ostream& Foam::UOPstream::write(const string& str)
 }
 
 
-Foam::Ostream& Foam::UOPstream::writeQuoted
+Foam::Ostream& Foam::UOPstreamBase::writeQuoted
 (
     const std::string& str,
     const bool quoted
@@ -310,7 +288,7 @@ Foam::Ostream& Foam::UOPstream::writeQuoted
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const int32_t val)
+Foam::Ostream& Foam::UOPstreamBase::write(const int32_t val)
 {
     putChar(token::tokenType::LABEL);
     writeToBuffer(val);
@@ -318,7 +296,7 @@ Foam::Ostream& Foam::UOPstream::write(const int32_t val)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const int64_t val)
+Foam::Ostream& Foam::UOPstreamBase::write(const int64_t val)
 {
     putChar(token::tokenType::LABEL);
     writeToBuffer(val);
@@ -326,7 +304,7 @@ Foam::Ostream& Foam::UOPstream::write(const int64_t val)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const floatScalar val)
+Foam::Ostream& Foam::UOPstreamBase::write(const floatScalar val)
 {
     putChar(token::tokenType::FLOAT);
     writeToBuffer(val);
@@ -334,7 +312,7 @@ Foam::Ostream& Foam::UOPstream::write(const floatScalar val)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const doubleScalar val)
+Foam::Ostream& Foam::UOPstreamBase::write(const doubleScalar val)
 {
     putChar(token::tokenType::DOUBLE);
     writeToBuffer(val);
@@ -342,7 +320,7 @@ Foam::Ostream& Foam::UOPstream::write(const doubleScalar val)
 }
 
 
-Foam::Ostream& Foam::UOPstream::write(const char* data, std::streamsize count)
+Foam::Ostream& Foam::UOPstreamBase::write(const char* data, std::streamsize count)
 {
     if (format() != BINARY)
     {
@@ -358,7 +336,7 @@ Foam::Ostream& Foam::UOPstream::write(const char* data, std::streamsize count)
 }
 
 
-Foam::Ostream& Foam::UOPstream::writeRaw
+Foam::Ostream& Foam::UOPstreamBase::writeRaw
 (
     const char* data,
     std::streamsize count
@@ -374,7 +352,7 @@ Foam::Ostream& Foam::UOPstream::writeRaw
 }
 
 
-bool Foam::UOPstream::beginRawWrite(std::streamsize count)
+bool Foam::UOPstreamBase::beginRawWrite(std::streamsize count)
 {
     if (format() != BINARY)
     {
@@ -391,7 +369,7 @@ bool Foam::UOPstream::beginRawWrite(std::streamsize count)
 }
 
 
-void Foam::UOPstream::print(Ostream& os) const
+void Foam::UOPstreamBase::print(Ostream& os) const
 {
     os  << "Writing from processor " << toProcNo_
         << " to processor " << myProcNo() << " in communicator " << comm_
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.C b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.C
index 00883ca011..8c6df7a971 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.C
+++ b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.C
@@ -38,11 +38,12 @@ namespace Foam
 
 // * * * * * * * * * * * * * Private Member Functions *  * * * * * * * * * * //
 
-void Foam::processorLduInterface::resizeBuf(List<char>& buf, const label size)
+void Foam::processorLduInterface::resizeBuf(List<char>& buf, const label len)
 {
-    if (buf.size() < size)
+    if (buf.size() < len)
     {
-        buf.resize(size);
+        // Use nocopy variant since it will be overwritten
+        buf.resize_nocopy(len);
     }
 }
 
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.H b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.H
index d3a6a7801c..28c13b7e25 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.H
+++ b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterface.H
@@ -36,8 +36,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef processorLduInterface_H
-#define processorLduInterface_H
+#ifndef Foam_processorLduInterface_H
+#define Foam_processorLduInterface_H
 
 #include "lduInterface.H"
 #include "primitiveFieldsFwd.H"
@@ -67,7 +67,7 @@ class processorLduInterface
     // Private Member Functions
 
         //- Increase buffer size if required
-        static void resizeBuf(List<char>& buf, const label size);
+        static void resizeBuf(List<char>& buf, const label len);
 
 
 public:
@@ -78,7 +78,7 @@ public:
 
     // Constructors
 
-        //- Construct null
+        //- Default construct
         processorLduInterface() = default;
 
 
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
index 70a5639ef6..fa2292c6e5 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
+++ b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
@@ -39,7 +39,7 @@ void Foam::processorLduInterface::send
     const UList<Type>& f
 ) const
 {
-    label nBytes = f.byteSize();
+    const label nBytes = f.byteSize();
 
     if
     (
diff --git a/src/Pstream/dummy/Make/files b/src/Pstream/dummy/Make/files
index c025891574..d1d6ee3207 100644
--- a/src/Pstream/dummy/Make/files
+++ b/src/Pstream/dummy/Make/files
@@ -1,5 +1,6 @@
 UPstream.C
-UIPread.C
-UOPwrite.C
+
+UIPstreamRead.C
+UOPstreamWrite.C
 
 LIB = $(FOAM_LIBBIN)/dummy/libPstream
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/OPstream.C b/src/Pstream/dummy/UIPstreamRead.C
similarity index 72%
rename from src/OpenFOAM/db/IOstreams/Pstreams/OPstream.C
rename to src/Pstream/dummy/UIPstreamRead.C
index 75805c718d..3fef73615b 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/OPstream.C
+++ b/src/Pstream/dummy/UIPstreamRead.C
@@ -5,8 +5,8 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2011-2013 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2011-2015 OpenFOAM Foundation
+    Copyright (C) 2021-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -26,32 +26,31 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-#include "OPstream.H"
+#include "UIPstream.H"
 
-// * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
-Foam::OPstream::OPstream
+void Foam::UIPstream::bufferIPCrecv()
+{
+    NotImplemented;
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+Foam::label Foam::UIPstream::read
 (
     const commsTypes commsType,
-    const int toProcNo,
-    const label bufSize,
+    const int fromProcNo,
+    char* buf,
+    const std::streamsize bufSize,
     const int tag,
-    const label comm,
-    IOstreamOption::streamFormat fmt
+    const label communicator
 )
-:
-    Pstream(commsType, bufSize),
-    UOPstream
-    (
-        commsType,
-        toProcNo,
-        Pstream::transferBuf_,
-        tag,
-        comm,
-        true,  // sendAtDestruct
-        fmt
-    )
-{}
+{
+    NotImplemented;
+    return 0;
+}
 
 
 // ************************************************************************* //
diff --git a/src/Pstream/dummy/UOPwrite.C b/src/Pstream/dummy/UOPstreamWrite.C
similarity index 89%
rename from src/Pstream/dummy/UOPwrite.C
rename to src/Pstream/dummy/UOPstreamWrite.C
index fa1c2991f5..9acde63b74 100644
--- a/src/Pstream/dummy/UOPwrite.C
+++ b/src/Pstream/dummy/UOPstreamWrite.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2015 OpenFOAM Foundation
+    Copyright (C) 2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -23,13 +24,19 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-Description
-    Write primitive and binary block from OPstream
-
 \*---------------------------------------------------------------------------*/
 
 #include "UOPstream.H"
 
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+bool Foam::UOPstream::bufferIPCsend()
+{
+    NotImplemented;
+    return false;
+}
+
+
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 bool Foam::UOPstream::write
@@ -43,7 +50,6 @@ bool Foam::UOPstream::write
 )
 {
     NotImplemented;
-
     return false;
 }
 
diff --git a/src/Pstream/mpi/Make/files b/src/Pstream/mpi/Make/files
index eccdf77664..e16e96a25f 100644
--- a/src/Pstream/mpi/Make/files
+++ b/src/Pstream/mpi/Make/files
@@ -1,6 +1,7 @@
-UOPwrite.C
-UIPread.C
-UPstream.C
 PstreamGlobals.C
+UPstream.C
+
+UIPstreamRead.C
+UOPstreamWrite.C
 
 LIB = $(FOAM_MPI_LIBBIN)/libPstream
diff --git a/src/Pstream/mpi/UIPread.C b/src/Pstream/mpi/UIPstreamRead.C
similarity index 52%
rename from src/Pstream/mpi/UIPread.C
rename to src/Pstream/mpi/UIPstreamRead.C
index bd8b318899..c1bf6fd1d4 100644
--- a/src/Pstream/mpi/UIPread.C
+++ b/src/Pstream/mpi/UIPstreamRead.C
@@ -24,9 +24,6 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-Description
-    Read from UIPstream
-
 \*---------------------------------------------------------------------------*/
 
 #include "UIPstream.H"
@@ -36,195 +33,64 @@ Description
 
 #include <mpi.h>
 
-// * * * * * * * * * * * * * * * * Constructor * * * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
-Foam::UIPstream::UIPstream
-(
-    const commsTypes commsType,
-    const int fromProcNo,
-    DynamicList<char>& receiveBuf,
-    label& receiveBufPosition,
-    const int tag,
-    const label comm,
-    const bool clearAtEnd,
-    IOstreamOption::streamFormat fmt
-)
-:
-    UPstream(commsType),
-    Istream(fmt, IOstreamOption::currentVersion),
-    fromProcNo_(fromProcNo),
-    recvBuf_(receiveBuf),
-    recvBufPos_(receiveBufPosition),
-    tag_(tag),
-    comm_(comm),
-    clearAtEnd_(clearAtEnd),
-    messageSize_(0)
+void Foam::UIPstream::bufferIPCrecv()
 {
-    setOpened();
-    setGood();
-
-    if (commsType == commsTypes::nonBlocking)
+    // Called by constructor
+    if (debug)
     {
-        // Message is already received into buffer
+        Pout<< "UIPstream IPC read buffer :"
+            << " from:" << fromProcNo_
+            << " tag:" << tag_ << " comm:" << comm_
+            << " wanted size:" << recvBuf_.capacity()
+            << Foam::endl;
     }
-    else
+
+    // No buffer size allocated/specified - probe size of incoming message
+    if (!recvBuf_.capacity())
     {
-        if (debug)
-        {
-            Pout<< "UIPstream::UIPstream :"
-                << " read from:" << fromProcNo
-                << " tag:" << tag_ << " comm:" << comm_
-                << " wanted size:" << recvBuf_.capacity()
-                << Foam::endl;
-        }
+        profilingPstream::beginTiming();
 
-        // No buffer size allocated/specified - probe size of incoming message
-        if (!recvBuf_.capacity())
-        {
-            profilingPstream::beginTiming();
+        MPI_Status status;
 
-            MPI_Status status;
-
-            MPI_Probe
-            (
-                fromProcNo_,
-                tag_,
-                PstreamGlobals::MPICommunicators_[comm_],
-                &status
-            );
-            MPI_Get_count(&status, MPI_BYTE, &messageSize_);
-
-            // Assume these are from gathers ...
-            profilingPstream::addGatherTime();
-
-            recvBuf_.resize(messageSize_);
-
-            if (debug)
-            {
-                Pout<< "UIPstream::UIPstream : probed size:"
-                    << messageSize_ << Foam::endl;
-            }
-        }
-
-        messageSize_ = UIPstream::read
+        MPI_Probe
         (
-            commsType,
             fromProcNo_,
-            recvBuf_.data(),
-            recvBuf_.capacity(),
             tag_,
-            comm_
+            PstreamGlobals::MPICommunicators_[comm_],
+            &status
         );
+        MPI_Get_count(&status, MPI_BYTE, &messageSize_);
+
+        // Assume these are from gathers ...
+        profilingPstream::addGatherTime();
 
-        // Set addressed size. Leave actual allocated memory intact.
         recvBuf_.resize(messageSize_);
 
-        if (!messageSize_)
+        if (debug)
         {
-            setEof();
+            Pout<< "UIPstream::UIPstream : probed size:"
+                << messageSize_ << Foam::endl;
         }
     }
-}
 
-
-Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
-:
-    UPstream(buffers.commsType_),
-    Istream(buffers.format_, IOstreamOption::currentVersion),
-    fromProcNo_(fromProcNo),
-    recvBuf_(buffers.recvBuf_[fromProcNo]),
-    recvBufPos_(buffers.recvBufPos_[fromProcNo]),
-    tag_(buffers.tag_),
-    comm_(buffers.comm_),
-    clearAtEnd_(true),
-    messageSize_(0)
-{
-    if
+    messageSize_ = UIPstream::read
     (
-        commsType() != UPstream::commsTypes::scheduled
-     && !buffers.finishedSendsCalled_
-    )
+        commsType_,
+        fromProcNo_,
+        recvBuf_.data(),
+        recvBuf_.capacity(),
+        tag_,
+        comm_
+    );
+
+    // Set addressed size. Leave actual allocated memory intact.
+    recvBuf_.resize(messageSize_);
+
+    if (!messageSize_)
     {
-        FatalErrorInFunction
-            << "PstreamBuffers::finishedSends() never called." << endl
-            << "Please call PstreamBuffers::finishedSends() after doing"
-            << " all your sends (using UOPstream) and before doing any"
-            << " receives (using UIPstream)" << Foam::exit(FatalError);
-    }
-
-    setOpened();
-    setGood();
-
-    if (commsType() == commsTypes::nonBlocking)
-    {
-        // Message is already received into buffer
-        messageSize_ = recvBuf_.size();
-
-        if (debug)
-        {
-            Pout<< "UIPstream::UIPstream PstreamBuffers :"
-                << " fromProcNo:" << fromProcNo
-                << " tag:" << tag_ << " comm:" << comm_
-                << " receive buffer size:" << messageSize_
-                << Foam::endl;
-        }
-    }
-    else
-    {
-        if (debug)
-        {
-            Pout<< "UIPstream::UIPstream PstreamBuffers :"
-                << " read from:" << fromProcNo
-                << " tag:" << tag_ << " comm:" << comm_
-                << " wanted size:" << recvBuf_.capacity()
-                << Foam::endl;
-        }
-
-        // No buffer size allocated/specified - probe size of incoming message
-        if (!recvBuf_.capacity())
-        {
-            profilingPstream::beginTiming();
-
-            MPI_Status status;
-
-            MPI_Probe
-            (
-                fromProcNo_,
-                tag_,
-                PstreamGlobals::MPICommunicators_[comm_],
-                &status
-            );
-            MPI_Get_count(&status, MPI_BYTE, &messageSize_);
-
-            // Assume these are from gathers ...
-            profilingPstream::addGatherTime();
-
-            recvBuf_.resize(messageSize_);
-
-            if (debug)
-            {
-                Pout<< "UIPstream::UIPstream PstreamBuffers : probed size:"
-                    << messageSize_ << Foam::endl;
-            }
-        }
-
-        messageSize_ = UIPstream::read
-        (
-            commsType(),
-            fromProcNo_,
-            recvBuf_.data(),
-            recvBuf_.capacity(),
-            tag_,
-            comm_
-        );
-
-        // Set addressed size. Leave actual allocated memory intact.
-        recvBuf_.resize(messageSize_);
-
-        if (!messageSize_)
-        {
-            setEof();
-        }
+        setEof();
     }
 }
 
@@ -287,7 +153,6 @@ Foam::label Foam::UIPstream::read
             FatalErrorInFunction
                 << "MPI_Recv cannot receive incoming message"
                 << Foam::abort(FatalError);
-
             return 0;
         }
 
@@ -336,7 +201,7 @@ Foam::label Foam::UIPstream::read
         )
         {
             FatalErrorInFunction
-                << "MPI_Recv cannot start non-blocking receive"
+                << "MPI_Irecv cannot start non-blocking receive"
                 << Foam::abort(FatalError);
 
             return 0;
diff --git a/src/Pstream/mpi/UOPwrite.C b/src/Pstream/mpi/UOPstreamWrite.C
similarity index 90%
rename from src/Pstream/mpi/UOPwrite.C
rename to src/Pstream/mpi/UOPstreamWrite.C
index f59fba924d..0ff30ff98d 100644
--- a/src/Pstream/mpi/UOPwrite.C
+++ b/src/Pstream/mpi/UOPstreamWrite.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -24,9 +24,6 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-Description
-    Write primitive and binary block from OPstream
-
 \*---------------------------------------------------------------------------*/
 
 #include "UOPstream.H"
@@ -35,6 +32,22 @@ Description
 
 #include <mpi.h>
 
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+bool Foam::UOPstream::bufferIPCsend()
+{
+    return UOPstream::write
+    (
+        commsType_,
+        toProcNo_,
+        sendBuf_.cdata(),
+        sendBuf_.size(),
+        tag_,
+        comm_
+    );
+}
+
+
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 bool Foam::UOPstream::write
@@ -70,13 +83,13 @@ bool Foam::UOPstream::write
     PstreamGlobals::checkCommunicator(communicator, toProcNo);
 
 
-    bool transferFailed = true;
+    bool failed = true;
 
     profilingPstream::beginTiming();
 
     if (commsType == commsTypes::blocking)
     {
-        transferFailed = MPI_Bsend
+        failed = MPI_Bsend
         (
             const_cast<char*>(buf),
             bufSize,
@@ -99,7 +112,7 @@ bool Foam::UOPstream::write
     }
     else if (commsType == commsTypes::scheduled)
     {
-        transferFailed = MPI_Send
+        failed = MPI_Send
         (
             const_cast<char*>(buf),
             bufSize,
@@ -124,7 +137,7 @@ bool Foam::UOPstream::write
     {
         MPI_Request request;
 
-        transferFailed = MPI_Isend
+        failed = MPI_Isend
         (
             const_cast<char*>(buf),
             bufSize,
@@ -151,12 +164,11 @@ bool Foam::UOPstream::write
     else
     {
         FatalErrorInFunction
-            << "Unsupported communications type "
-            << UPstream::commsTypeNames[commsType]
+            << "Unsupported communications type " << int(commsType)
             << Foam::abort(FatalError);
     }
 
-    return !transferFailed;
+    return !failed;
 }
 
 
diff --git a/src/finiteArea/faMesh/faPatches/constraint/processor/processorFaPatch.C b/src/finiteArea/faMesh/faPatches/constraint/processor/processorFaPatch.C
index 4ac1c79f22..fab3a58e1b 100644
--- a/src/finiteArea/faMesh/faPatches/constraint/processor/processorFaPatch.C
+++ b/src/finiteArea/faMesh/faPatches/constraint/processor/processorFaPatch.C
@@ -28,8 +28,6 @@ License
 
 #include "processorFaPatch.H"
 #include "addToRunTimeSelectionTable.H"
-#include "IPstream.H"
-#include "OPstream.H"
 #include "transformField.H"
 #include "faBoundaryMesh.H"
 #include "faMesh.H"
diff --git a/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.C b/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.C
index 5c24cc8a1f..613fd7ce57 100644
--- a/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.C
+++ b/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.C
@@ -28,8 +28,6 @@ License
 
 #include "processorFaPatchField.H"
 #include "processorFaPatch.H"
-#include "IPstream.H"
-#include "OPstream.H"
 #include "transformField.H"
 
 // * * * * * * * * * * * * * * * * Constructors * * * * * * * * * * * * * * //
diff --git a/src/meshTools/algorithms/MeshWave/FaceCellWave.C b/src/meshTools/algorithms/MeshWave/FaceCellWave.C
index 8de0d33767..89c15a2fa4 100644
--- a/src/meshTools/algorithms/MeshWave/FaceCellWave.C
+++ b/src/meshTools/algorithms/MeshWave/FaceCellWave.C
@@ -31,8 +31,8 @@ License
 #include "processorPolyPatch.H"
 #include "cyclicPolyPatch.H"
 #include "cyclicAMIPolyPatch.H"
-#include "OPstream.H"
-#include "IPstream.H"
+#include "UIPstream.H"
+#include "UOPstream.H"
 #include "PstreamReduceOps.H"
 #include "debug.H"
 #include "typeInfo.H"
diff --git a/src/meshTools/algorithms/PointEdgeWave/PointEdgeWave.C b/src/meshTools/algorithms/PointEdgeWave/PointEdgeWave.C
index 52604c021a..2a6357835b 100644
--- a/src/meshTools/algorithms/PointEdgeWave/PointEdgeWave.C
+++ b/src/meshTools/algorithms/PointEdgeWave/PointEdgeWave.C
@@ -30,8 +30,8 @@ License
 #include "polyMesh.H"
 #include "processorPolyPatch.H"
 #include "cyclicPolyPatch.H"
-#include "OPstream.H"
-#include "IPstream.H"
+#include "UIPstream.H"
+#include "UOPstream.H"
 #include "PstreamCombineReduceOps.H"
 #include "debug.H"
 #include "typeInfo.H"