diff --git a/applications/test/parallel-comm1/Test-parallel-comm1.C b/applications/test/parallel-comm1/Test-parallel-comm1.C
index d0bc966a5d..33a6bd5bdc 100644
--- a/applications/test/parallel-comm1/Test-parallel-comm1.C
+++ b/applications/test/parallel-comm1/Test-parallel-comm1.C
@@ -62,7 +62,7 @@ scalar sumReduce
                 scalar procValue;
                 UIPstream::read
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     proci,
                     reinterpret_cast<char*>(&procValue),
                     sizeof(scalar),
@@ -79,7 +79,7 @@ scalar sumReduce
             {
                 UOPstream::write
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     proci,
                     reinterpret_cast<const char*>(&sum),
                     sizeof(scalar),
@@ -93,7 +93,7 @@ scalar sumReduce
             {
                 UOPstream::write
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     UPstream::masterNo(),
                     reinterpret_cast<const char*>(&localValue),
                     sizeof(scalar),
@@ -105,7 +105,7 @@ scalar sumReduce
             {
                 UIPstream::read
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     UPstream::masterNo(),
                     reinterpret_cast<char*>(&sum),
                     sizeof(scalar),
diff --git a/applications/test/parallel/Test-parallel.C b/applications/test/parallel/Test-parallel.C
index 06d3ea16e9..fa6ab72bee 100644
--- a/applications/test/parallel/Test-parallel.C
+++ b/applications/test/parallel/Test-parallel.C
@@ -131,7 +131,7 @@ void testTransfer(const T& input)
         for (const int proci : UPstream::subProcs())
         {
             Perr<< "master sending to proc:" << proci << endl;
-            OPstream os(UPstream::commsTypes::blocking, proci);
+            OPstream os(UPstream::commsTypes::buffered, proci);
             os  << data;
         }
     }
@@ -139,7 +139,7 @@ void testTransfer(const T& input)
     {
         {
             Perr<< "proc sending to master" << endl;
-            OPstream os(UPstream::commsTypes::blocking, UPstream::masterNo());
+            OPstream os(UPstream::commsTypes::buffered, UPstream::masterNo());
             os  << data;
         }
 
@@ -169,7 +169,7 @@ void testTokenized(const T& data)
         for (const int proci : UPstream::subProcs())
         {
             Perr<< "master sending to proc:" << proci << endl;
-            OPstream os(UPstream::commsTypes::blocking, proci);
+            OPstream os(UPstream::commsTypes::buffered, proci);
             os  << tok;
         }
     }
@@ -177,7 +177,7 @@ void testTokenized(const T& data)
     {
         {
             Perr<< "proc sending to master" << endl;
-            OPstream os(UPstream::commsTypes::blocking, UPstream::masterNo());
+            OPstream os(UPstream::commsTypes::buffered, UPstream::masterNo());
             os  << tok;
         }
 
diff --git a/applications/test/surface-sampling/mydebugSurfaceWriter.H b/applications/test/surface-sampling/mydebugSurfaceWriter.H
index 825cde7e4f..cfaea6f808 100644
--- a/applications/test/surface-sampling/mydebugSurfaceWriter.H
+++ b/applications/test/surface-sampling/mydebugSurfaceWriter.H
@@ -44,7 +44,7 @@ Description
     Format options:
     \table
         Property    | Description                           | Required | Default
-        commsType   | blocking/nonBlocking/scheduled        | no  | scheduled
+        commsType   | scheduled/nonBlocking/buffered        | no  | scheduled
         merge       | Enable geometry/field merging         | no  | true
         write       | Write file(s)                         | no  | false
         narrow      | Communicate with narrowed values      | no  | false
diff --git a/applications/utilities/mesh/manipulation/createPatch/createPatch.C b/applications/utilities/mesh/manipulation/createPatch/createPatch.C
index 133d208d96..f07f49bfad 100644
--- a/applications/utilities/mesh/manipulation/createPatch/createPatch.C
+++ b/applications/utilities/mesh/manipulation/createPatch/createPatch.C
@@ -568,10 +568,9 @@ void syncPoints
                     }
                 }
 
-                // buffered send
                 OPstream toNbr
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     procPatch.neighbProcNo()
                 );
                 toNbr << patchInfo;
diff --git a/applications/utilities/preProcessing/mapFieldsPar/MapVolFields.H b/applications/utilities/preProcessing/mapFieldsPar/MapVolFields.H
index 1257d47aeb..f3106def5c 100644
--- a/applications/utilities/preProcessing/mapFieldsPar/MapVolFields.H
+++ b/applications/utilities/preProcessing/mapFieldsPar/MapVolFields.H
@@ -48,7 +48,7 @@ void evaluateConstraintTypes(GeometricField<Type, fvPatchField, volMesh>& fld)
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
diff --git a/etc/controlDict b/etc/controlDict
index f084663716..d0ffb76552 100644
--- a/etc/controlDict
+++ b/etc/controlDict
@@ -132,7 +132,7 @@ OptimisationSwitches
     // MPI/Parallel settings
     // =====================
 
-    // Default communication type (nonBlocking | scheduled | blocking);
+    // Default communication type (nonBlocking | scheduled | buffered)
     commsType       nonBlocking;
 
     // Transfer double as float for processor boundaries. Mostly defunct.
diff --git a/src/OpenFOAM/containers/Lists/SortableList/ParSortableList.C b/src/OpenFOAM/containers/Lists/SortableList/ParSortableList.C
index d5f8ad2cd9..5917575603 100644
--- a/src/OpenFOAM/containers/Lists/SortableList/ParSortableList.C
+++ b/src/OpenFOAM/containers/Lists/SortableList/ParSortableList.C
@@ -115,7 +115,7 @@ void Foam::ParSortableList<Type>::checkAndSend
         }
 
         {
-            OPstream toProc(UPstream::commsTypes::blocking, destProci);
+            OPstream toProc(UPstream::commsTypes::buffered, destProci);
             toProc << values << indices;
         }
     }
@@ -309,7 +309,7 @@ void Foam::ParSortableList<Type>::sort()
                     Pout<< "Receiving from " << proci << endl;
                 }
 
-                IPstream fromProc(UPstream::commsTypes::blocking, proci);
+                IPstream fromProc(UPstream::commsTypes::buffered, proci);
 
                 fromProc >> recValues >> recIndices;
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C b/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
index e956e8de74..fc8312f674 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/OPstreams.C
@@ -101,6 +101,12 @@ Foam::UOPstream::~UOPstream()
 {
     if (sendAtDestruct_)
     {
+        // Note: sendAtDestruct_ and nonBlocking is a questionable combination
+        // since the transfer buffer will be destroyed before
+        // the non-blocking send completes!
+        //
+        // Could flag as an error, but not actually used anywhere.
+
         if (!bufferIPCsend())
         {
             FatalErrorInFunction
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
index e61bf65e90..cb4cf58e3a 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
+++ b/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 non-blocking. Does
+    of received buffers. Works with both buffered and non-blocking. Does
     not make much sense with scheduled since there you would not need these
     explicit buffers.
 
@@ -51,7 +51,7 @@ Description
             }
         }
 
-        pBufs.finishedSends();   // no-op for blocking
+        pBufs.finishedSends();   // no-op for buffered
 
         for (const int proci : UPstream::allProcs())
         {
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstream.H
index 3e70872c34..138dc465a8 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) 2017-2023 OpenCFD Ltd.
+    Copyright (C) 2017-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -96,7 +96,7 @@ protected:
         const int comm_;
 
         //- The message size, read on bufferIPCrecv or set directly
-        int messageSize_;
+        label messageSize_;
 
         //- Receive position in buffer data, if ony
         //- If there is no external location for recvBufPos_
@@ -279,8 +279,8 @@ public:
     // Static Functions
 
         //- Read buffer contents from given processor.
-        //  \return the message size (bytes read)
-        static label read
+        //  \return the message size (bytes read). May change in the future
+        static std::streamsize read
         (
             const UPstream::commsTypes commsType,
             const int fromProcNo,
@@ -293,8 +293,8 @@ public:
         );
 
         //- Read buffer contents (non-blocking) from given processor.
-        //  \return the message size (bytes read)
-        inline static label read
+        //  \return the message size (bytes read). May change in the future
+        inline static std::streamsize read
         (
             //! [out] request information
             UPstream::Request& req,
@@ -321,7 +321,7 @@ public:
         //  Only valid for contiguous data types.
         //  \return the message size (bytes read). May change in the future
         template<class Type>
-        inline static label read
+        inline static std::streamsize read
         (
             const UPstream::commsTypes commsType,
             const int fromProcNo,
@@ -348,7 +348,7 @@ public:
         //  Only valid for contiguous data types.
         //  \return the message size (bytes read). May change in the future
         template<class Type>
-        inline static label read
+        inline static std::streamsize read
         (
             const UPstream::commsTypes commsType,
             const int fromProcNo,
@@ -375,7 +375,7 @@ public:
         //  Only valid for contiguous data types.
         //  \return the message size (bytes read). May change in the future
         template<class Type>
-        inline static label read
+        inline static std::streamsize read
         (
             //! [out] request information
             UPstream::Request& req,
@@ -401,7 +401,7 @@ public:
         //  Only valid for contiguous data types.
         //  \return the message size (bytes read). May change in the future
         template<class Type>
-        inline static label read
+        inline static std::streamsize read
         (
             //! [out] request information
             UPstream::Request& req,
@@ -474,8 +474,8 @@ public:
     // Static Functions
 
         //- Wrapped version of UPstream::broadcast
-        //  \return the message size (bytes read)
-        static label read
+        //  \return the message size (bytes read). May change in the future
+        static std::streamsize read
         (
             const int rootProcNo,  //!< normally UPstream::masterNo()
             char* buf,
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
index bdf79dd6cd..cf531d1014 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
@@ -50,9 +50,11 @@ const Foam::Enum
 >
 Foam::UPstream::commsTypeNames
 ({
-    { commsTypes::blocking, "blocking" },   // "buffered"
+    { commsTypes::buffered, "buffered" },   // "buffered"
     { commsTypes::scheduled, "scheduled" },
     { commsTypes::nonBlocking, "nonBlocking" },  // "immediate"
+    // compatibility names
+    { commsTypes::buffered, "blocking" },
 });
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
index bf22b7bac0..ee44634770 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
@@ -73,15 +73,17 @@ public:
     //- Communications types
     enum class commsTypes : char
     {
-        blocking,       //!< "blocking" (buffered)      : (MPI_Bsend, MPI_Recv)
+        buffered,       //!< "buffered"                 : (MPI_Bsend, MPI_Recv)
         scheduled,      //!< "scheduled" (MPI standard) : (MPI_Send, MPI_Recv)
-        nonBlocking     //!< "nonBlocking" (immediate)  : (MPI_Isend, MPI_Irecv)
+        nonBlocking,    //!< "nonBlocking" (immediate)  : (MPI_Isend, MPI_Irecv)
+        // Aliases
+        blocking = buffered  //!< compatibility name for buffered
     };
 
     //- Enumerated names for the communication types
     static const Enum<commsTypes> commsTypeNames;
 
-    //- Different MPI-send modes (ignored for commsTypes::blocking)
+    //- Different MPI-send modes (ignored for commsTypes::buffered)
     enum class sendModes : char
     {
         normal,         //!< (MPI_Send, MPI_Isend)
diff --git a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricBoundaryField.C b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricBoundaryField.C
index 0a16f916c3..70d5ce2556 100644
--- a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricBoundaryField.C
+++ b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricBoundaryField.C
@@ -598,7 +598,7 @@ void Foam::GeometricBoundaryField<Type, PatchField, GeoMesh>::evaluate()
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -689,7 +689,7 @@ void Foam::GeometricBoundaryField<Type, PatchField, GeoMesh>::evaluateLocal()
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -755,7 +755,7 @@ Foam::GeometricBoundaryField<Type, PatchField, GeoMesh>
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
diff --git a/src/OpenFOAM/fields/pointPatchFields/basic/basicSymmetry/basicSymmetryPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/basic/basicSymmetry/basicSymmetryPointPatchField.H
index 20cb347469..d132cc222b 100644
--- a/src/OpenFOAM/fields/pointPatchFields/basic/basicSymmetry/basicSymmetryPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/basic/basicSymmetry/basicSymmetryPointPatchField.H
@@ -111,7 +111,7 @@ public:
         //- Update the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         );
 
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/basic/coupled/coupledPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/basic/coupled/coupledPointPatchField.H
index a70e06f732..68d71f61ef 100644
--- a/src/OpenFOAM/fields/pointPatchFields/basic/coupled/coupledPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/basic/coupled/coupledPointPatchField.H
@@ -119,7 +119,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             ) = 0;
 
             //- Initialise swap of patch point values
diff --git a/src/OpenFOAM/fields/pointPatchFields/basic/value/valuePointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/basic/value/valuePointPatchField.H
index a4f7c2b205..4a71dd3766 100644
--- a/src/OpenFOAM/fields/pointPatchFields/basic/value/valuePointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/basic/value/valuePointPatchField.H
@@ -202,7 +202,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/cyclic/cyclicPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/cyclic/cyclicPointPatchField.H
index 80e5905a4e..d28e884605 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/cyclic/cyclicPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/cyclic/cyclicPointPatchField.H
@@ -152,7 +152,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/cyclicSlip/cyclicSlipPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/cyclicSlip/cyclicSlipPointPatchField.H
index 628ae11ae9..08479d9bf5 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/cyclicSlip/cyclicSlipPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/cyclicSlip/cyclicSlipPointPatchField.H
@@ -115,7 +115,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/nonuniformTransformCyclic/nonuniformTransformCyclicPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/nonuniformTransformCyclic/nonuniformTransformCyclicPointPatchField.H
index 8808cc3a0a..67d90a5366 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/nonuniformTransformCyclic/nonuniformTransformCyclicPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/nonuniformTransformCyclic/nonuniformTransformCyclicPointPatchField.H
@@ -115,7 +115,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/processor/processorPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/processor/processorPointPatchField.H
index 61f0962398..6fa9bf6cac 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/processor/processorPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/processor/processorPointPatchField.H
@@ -154,7 +154,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/processorCyclic/processorCyclicPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/processorCyclic/processorCyclicPointPatchField.H
index a5eed9049d..147fd58cf9 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/processorCyclic/processorCyclicPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/processorCyclic/processorCyclicPointPatchField.H
@@ -153,7 +153,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/symmetryPlane/symmetryPlanePointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/symmetryPlane/symmetryPlanePointPatchField.H
index 1b9b545902..b3b62e8c69 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/symmetryPlane/symmetryPlanePointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/symmetryPlane/symmetryPlanePointPatchField.H
@@ -126,7 +126,7 @@ public:
         //- Update the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/constraint/wedge/wedgePointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/constraint/wedge/wedgePointPatchField.H
index 436076f521..31f2bd75d9 100644
--- a/src/OpenFOAM/fields/pointPatchFields/constraint/wedge/wedgePointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/constraint/wedge/wedgePointPatchField.H
@@ -121,7 +121,7 @@ public:
         //- Update the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.C b/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.C
index 69bef4e188..c5f75450c6 100644
--- a/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.C
+++ b/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.C
@@ -192,7 +192,7 @@ Foam::codedFixedValuePointPatchField<Type>::codedFixedValuePointPatchField
         this->extrapolateInternal();
 
         // Evaluate to assign a value
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.H
index 9999047742..af76e7d974 100644
--- a/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/derived/codedFixedValue/codedFixedValuePointPatchField.H
@@ -243,7 +243,7 @@ public:
         //- Evaluate the patch field, sets updated() to false
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/OpenFOAM/fields/pointPatchFields/derived/fixedNormalSlip/fixedNormalSlipPointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/derived/fixedNormalSlip/fixedNormalSlipPointPatchField.H
index bdfa66a5a8..8cbb45142d 100644
--- a/src/OpenFOAM/fields/pointPatchFields/derived/fixedNormalSlip/fixedNormalSlipPointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/derived/fixedNormalSlip/fixedNormalSlipPointPatchField.H
@@ -132,7 +132,7 @@ public:
         //- Update the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/OpenFOAM/fields/pointPatchFields/pointPatchField/pointPatchField.H b/src/OpenFOAM/fields/pointPatchFields/pointPatchField/pointPatchField.H
index 543b7f57cf..c2a47ce412 100644
--- a/src/OpenFOAM/fields/pointPatchFields/pointPatchField/pointPatchField.H
+++ b/src/OpenFOAM/fields/pointPatchFields/pointPatchField/pointPatchField.H
@@ -562,14 +562,14 @@ public:
         //- Initialise evaluation of the patch field (do nothing)
         virtual void initEvaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         )
         {}
 
         //- Evaluate the patch field, sets updated() to false
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         );
 
             //- Initialise the evaluation of the patch field after a local
@@ -577,7 +577,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -585,7 +585,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C b/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
index a3fa3d2bb1..91423a6ca2 100644
--- a/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
+++ b/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
@@ -44,7 +44,7 @@ void Foam::LduMatrix<Type, DType, LUType>::initMatrixInterfaces
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -88,7 +88,7 @@ void Foam::LduMatrix<Type, DType, LUType>::initMatrixInterfaces
                     interfacei,
                     psiif,
                     interfaceCoeffs[interfacei],
-                    UPstream::commsTypes::blocking
+                    UPstream::commsTypes::buffered
                 );
             }
         }
@@ -172,7 +172,7 @@ void Foam::LduMatrix<Type, DType, LUType>::updateMatrixInterfaces
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -184,7 +184,7 @@ void Foam::LduMatrix<Type, DType, LUType>::updateMatrixInterfaces
         }
 
         // Check/no-check for updatedMatrix() ?
-        const bool noCheck = (commsType == UPstream::commsTypes::blocking);
+        const bool noCheck = (commsType == UPstream::commsTypes::buffered);
 
         forAll(interfaces_, interfacei)
         {
@@ -264,7 +264,7 @@ void Foam::LduMatrix<Type, DType, LUType>::updateMatrixInterfaces
                     interfacei,
                     psiif,
                     interfaceCoeffs[interfacei],
-                    UPstream::commsTypes::blocking
+                    UPstream::commsTypes::buffered
                 );
             }
         }
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
index 2a0c06c607..6d95e5215a 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
+++ b/src/OpenFOAM/matrices/lduMatrix/lduAddressing/lduInterface/processorLduInterfaceTemplates.C
@@ -43,7 +43,7 @@ void Foam::processorLduInterface::send
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::scheduled
     )
     {
@@ -113,7 +113,7 @@ void Foam::processorLduInterface::receive
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::scheduled
     )
     {
@@ -194,7 +194,7 @@ void Foam::processorLduInterface::compressedSend
 
         if
         (
-            commsType == UPstream::commsTypes::blocking
+            commsType == UPstream::commsTypes::buffered
          || commsType == UPstream::commsTypes::scheduled
         )
         {
@@ -272,7 +272,7 @@ void Foam::processorLduInterface::compressedReceive
 
         if
         (
-            commsType == UPstream::commsTypes::blocking
+            commsType == UPstream::commsTypes::buffered
          || commsType == UPstream::commsTypes::scheduled
         )
         {
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C b/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
index b7434b7e1a..6b4f48dc36 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
+++ b/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
@@ -44,7 +44,7 @@ void Foam::lduMatrix::initMatrixInterfaces
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -90,7 +90,7 @@ void Foam::lduMatrix::initMatrixInterfaces
                     psiif,
                     coupleCoeffs[interfacei],
                     cmpt,
-                    UPstream::commsTypes::blocking
+                    UPstream::commsTypes::buffered
                 );
             }
         }
@@ -229,7 +229,7 @@ void Foam::lduMatrix::updateMatrixInterfaces
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
@@ -241,7 +241,7 @@ void Foam::lduMatrix::updateMatrixInterfaces
         }
 
         // Check/no-check for updatedMatrix() ?
-        const bool noCheck = (commsType == UPstream::commsTypes::blocking);
+        const bool noCheck = (commsType == UPstream::commsTypes::buffered);
 
         // Consume anything still outstanding
         forAll(interfaces, interfacei)
@@ -326,7 +326,7 @@ void Foam::lduMatrix::updateMatrixInterfaces
                     psiif,
                     coupleCoeffs[interfacei],
                     cmpt,
-                    UPstream::commsTypes::blocking
+                    UPstream::commsTypes::buffered
                 );
             }
         }
diff --git a/src/OpenFOAM/meshes/pointMesh/pointBoundaryMesh/pointBoundaryMesh.C b/src/OpenFOAM/meshes/pointMesh/pointBoundaryMesh/pointBoundaryMesh.C
index 83b28ba35b..266583000a 100644
--- a/src/OpenFOAM/meshes/pointMesh/pointBoundaryMesh/pointBoundaryMesh.C
+++ b/src/OpenFOAM/meshes/pointMesh/pointBoundaryMesh/pointBoundaryMesh.C
@@ -111,7 +111,7 @@ void Foam::pointBoundaryMesh::calcGeometry()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -157,7 +157,7 @@ void Foam::pointBoundaryMesh::movePoints(const pointField& p)
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -203,7 +203,7 @@ void Foam::pointBoundaryMesh::updateMesh()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
index 94a764b961..68b9662a77 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
@@ -494,7 +494,7 @@ void Foam::mapDistributeBase::distribute
         return;
     }
 
-    if (commsType == UPstream::commsTypes::blocking)
+    if (commsType == UPstream::commsTypes::buffered)
     {
         // Since buffered sending can reuse the field to collect the
         // received data.
@@ -939,7 +939,7 @@ void Foam::mapDistributeBase::distribute
         return;
     }
 
-    if (commsType == UPstream::commsTypes::blocking)
+    if (commsType == UPstream::commsTypes::buffered)
     {
         // Since buffered sending can reuse the field to collect the
         // received data.
diff --git a/src/OpenFOAM/meshes/polyMesh/polyBoundaryMesh/polyBoundaryMesh.C b/src/OpenFOAM/meshes/polyMesh/polyBoundaryMesh/polyBoundaryMesh.C
index 6936849531..f7332a1900 100644
--- a/src/OpenFOAM/meshes/polyMesh/polyBoundaryMesh/polyBoundaryMesh.C
+++ b/src/OpenFOAM/meshes/polyMesh/polyBoundaryMesh/polyBoundaryMesh.C
@@ -304,7 +304,7 @@ void Foam::polyBoundaryMesh::calcGeometry()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -1297,7 +1297,7 @@ void Foam::polyBoundaryMesh::movePoints(const pointField& p)
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -1347,7 +1347,7 @@ void Foam::polyBoundaryMesh::updateMesh()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
diff --git a/src/Pstream/dummy/UIPBstreamRead.C b/src/Pstream/dummy/UIPBstreamRead.C
index ac23ba916d..31e0f0743f 100644
--- a/src/Pstream/dummy/UIPBstreamRead.C
+++ b/src/Pstream/dummy/UIPBstreamRead.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2022-2023 OpenCFD Ltd.
+    Copyright (C) 2022-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,7 +37,7 @@ void Foam::UIPBstream::bufferIPCrecv()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-Foam::label Foam::UIPBstream::read
+std::streamsize Foam::UIPBstream::read
 (
     const int rootProcNo,
     char* buf,
diff --git a/src/Pstream/dummy/UIPstreamRead.C b/src/Pstream/dummy/UIPstreamRead.C
index 316550769e..c8b7286fdf 100644
--- a/src/Pstream/dummy/UIPstreamRead.C
+++ b/src/Pstream/dummy/UIPstreamRead.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2015 OpenFOAM Foundation
-    Copyright (C) 2021-2023 OpenCFD Ltd.
+    Copyright (C) 2021-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -38,7 +38,7 @@ void Foam::UIPstream::bufferIPCrecv()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-Foam::label Foam::UIPstream::read
+std::streamsize Foam::UIPstream::read
 (
     const UPstream::commsTypes commsType,
     const int fromProcNo,
diff --git a/src/Pstream/mpi/UIPBstreamRead.C b/src/Pstream/mpi/UIPBstreamRead.C
index f384c391eb..0ee1d63ce3 100644
--- a/src/Pstream/mpi/UIPBstreamRead.C
+++ b/src/Pstream/mpi/UIPBstreamRead.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2022-2023 OpenCFD Ltd.
+    Copyright (C) 2022-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -39,7 +39,7 @@ void Foam::UIPBstream::bufferIPCrecv()
 
     // Expected message size, similar to MPI_Probe
     // Same type must be expected in UOPBstream::bufferIPCsend()
-    label bufSize(0);
+    std::streamsize bufSize(0);
 
     // Broadcast #1 - data size
     if
@@ -47,7 +47,7 @@ void Foam::UIPBstream::bufferIPCrecv()
         !UPstream::broadcast
         (
             reinterpret_cast<char*>(&bufSize),
-            sizeof(label),
+            sizeof(std::streamsize),
             comm_,
             fromProcNo_  //< is actually rootProcNo
         )
@@ -63,46 +63,45 @@ void Foam::UIPBstream::bufferIPCrecv()
         Pout<< "UOPBstream IPC read buffer :"
             << " root:" << fromProcNo_
             << " comm:" << comm_
-            << " probed size:" << bufSize
+            << " probed size:" << label(bufSize)
             << " wanted size:" << recvBuf_.capacity()
             << Foam::endl;
     }
 
-    // No buffer size allocated/specified
-    if (!recvBuf_.capacity())
+
+    // Set buffer size, avoiding any copying and resize doubling etc.
+    recvBuf_.clear();
+    if (recvBuf_.capacity() < label(bufSize))
     {
-        recvBuf_.resize(bufSize);
+        recvBuf_.setCapacity_nocopy(label(bufSize));
     }
+    recvBuf_.resize_nocopy(label(bufSize));
 
     // This is the only real information we can trust
-    messageSize_ = bufSize;
+    messageSize_ = label(bufSize);
+
 
     // Broadcast #2 - data content
     // - skip if there is no data to receive
-
-    if (messageSize_)
-    {
-        if
+    if
+    (
+        (bufSize > 0)
+     && !UPstream::broadcast
         (
-            !UPstream::broadcast
-            (
-                recvBuf_.data(),
-                messageSize_,  // same as bufSize
-                comm_,
-                fromProcNo_  //< is actually rootProcNo
-            )
+            recvBuf_.data(),
+            recvBuf_.size(),  // same as bufSize
+            comm_,
+            fromProcNo_  //< is actually rootProcNo
         )
-        {
-            FatalErrorInFunction
-                << "MPI_Bcast failure receiving buffer data:" << bufSize << nl
-                << Foam::abort(FatalError);
-        }
+    )
+    {
+        FatalErrorInFunction
+            << "MPI_Bcast failure receiving buffer data:"
+            << recvBuf_.size() << nl
+            << Foam::abort(FatalError);
     }
 
-    // Set addressed size. Leave actual allocated memory intact.
-    recvBuf_.resize(messageSize_);
-
-    if (!messageSize_)
+    if (recvBuf_.empty())
     {
         setEof();
     }
@@ -111,7 +110,7 @@ void Foam::UIPBstream::bufferIPCrecv()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-Foam::label Foam::UIPBstream::read
+std::streamsize Foam::UIPBstream::read
 (
     const int rootProcNo,
     char* buf,
diff --git a/src/Pstream/mpi/UIPstreamRead.C b/src/Pstream/mpi/UIPstreamRead.C
index afee9a1905..c8e6de0d74 100644
--- a/src/Pstream/mpi/UIPstreamRead.C
+++ b/src/Pstream/mpi/UIPstreamRead.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019-2023 OpenCFD Ltd.
+    Copyright (C) 2019-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,9 +37,8 @@ License
 
 // * * * * * * * * * * * * * * * Local Functions * * * * * * * * * * * * * * //
 
-// General blocking/non-blocking MPI receive, optionally with probed
-// message information.
-static Foam::label UPstream_mpi_receive
+// General blocking/non-blocking MPI receive
+static std::streamsize UPstream_mpi_receive
 (
     const Foam::UPstream::commsTypes commsType,
     char* buf,
@@ -54,34 +53,48 @@ static Foam::label UPstream_mpi_receive
 
     PstreamGlobals::reset_request(req);
 
-    if (UPstream::debug)
+    // TODO: some corrective action, at least when not nonBlocking
+    #if 0
+    // No warnings here, just on the sender side.
+    if (bufSize > std::streamsize(INT_MAX))
     {
-        Pout<< "UIPstream::read : starting read from:" << fromProcNo
-            << " tag:" << tag << " comm:" << communicator
-            << " wanted size:" << label(bufSize)
-            << " commsType:" << UPstream::commsTypeNames[commsType]
-            << Foam::endl;
+        Perr<< "UIPstream::read() : from rank " << fromProcNo
+            << " exceeds INT_MAX bytes" << Foam::endl;
+        error::printStack(Perr);
     }
+    #endif
+
     if (UPstream::warnComm >= 0 && communicator != UPstream::warnComm)
     {
         Pout<< "UIPstream::read : starting read from:" << fromProcNo
+            << " size:" << label(bufSize)
             << " tag:" << tag << " comm:" << communicator
-            << " wanted size:" << label(bufSize)
             << " commsType:" << UPstream::commsTypeNames[commsType]
             << " warnComm:" << UPstream::warnComm
             << Foam::endl;
         error::printStack(Pout);
     }
+    else if (UPstream::debug)
+    {
+        Pout<< "UIPstream::read : starting read from:" << fromProcNo
+            << " size:" << label(bufSize)
+            << " tag:" << tag << " comm:" << communicator
+            << " commsType:" << UPstream::commsTypeNames[commsType]
+            << Foam::endl;
+    }
+
+    int returnCode = MPI_ERR_UNKNOWN;
 
     profilingPstream::beginTiming();
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::scheduled
     )
     {
-        int returnCode = 0;
+        // Not UPstream::commsTypes::nonBlocking
+
         MPI_Status status;
 
         {
@@ -97,6 +110,8 @@ static Foam::label UPstream_mpi_receive
             );
         }
 
+        profilingPstream::addGatherTime();
+
         if (returnCode != MPI_SUCCESS)
         {
             FatalErrorInFunction
@@ -104,36 +119,31 @@ static Foam::label UPstream_mpi_receive
                 << Foam::abort(FatalError);
             return 0;
         }
-
-        profilingPstream::addGatherTime();
-
-        // Check size of message read
-
-        int messageSize;
-        MPI_Get_count(&status, MPI_BYTE, &messageSize);
-
-        if (UPstream::debug)
+        else if (UPstream::debug)
         {
-            Pout<< "UIPstream::read : finished read from:" << fromProcNo
-                << " tag:" << tag << " read size:" << label(bufSize)
-                << " commsType:" << UPstream::commsTypeNames[commsType]
+            Pout<< "UIPstream::read : finished recv from:"
+                << fromProcNo
+                << " size:" << label(bufSize) << " tag:" << tag
                 << Foam::endl;
         }
 
-        if (messageSize > bufSize)
+        // Check size of message read
+        int count(0);
+        MPI_Get_count(&status, MPI_BYTE, &count);
+
+        if (bufSize < std::streamsize(count))
         {
             FatalErrorInFunction
                 << "buffer (" << label(bufSize)
                 << ") not large enough for incoming message ("
-                << messageSize << ')'
+                << label(count) << ')'
                 << Foam::abort(FatalError);
         }
 
-        return messageSize;
+        return std::streamsize(count);
     }
     else if (commsType == UPstream::commsTypes::nonBlocking)
     {
-        int returnCode = 0;
         MPI_Request request;
 
         {
@@ -158,19 +168,20 @@ static Foam::label UPstream_mpi_receive
             return 0;
         }
 
+        PstreamGlobals::push_request(request, req);
+        profilingPstream::addRequestTime();
+
+
         if (UPstream::debug)
         {
-            Pout<< "UIPstream::read : started read from:" << fromProcNo
-                << " tag:" << tag << " read size:" << label(bufSize)
-                << " commsType:" << UPstream::commsTypeNames[commsType]
+            Pout<< "UIPstream::read : started non-blocking recv from:"
+                << fromProcNo
+                << " size:" << label(bufSize) << " tag:" << tag
                 << " request:" <<
                 (req ? label(-1) : PstreamGlobals::outstandingRequests_.size())
                 << Foam::endl;
         }
 
-        PstreamGlobals::push_request(request, req);
-        profilingPstream::addRequestTime();
-
         // Assume the message will be completely received.
         return bufSize;
     }
@@ -197,9 +208,24 @@ void Foam::UIPstream::bufferIPCrecv()
             << Foam::endl;
     }
 
-    // No buffer size allocated/specified - probe size of incoming message
-    if (!recvBuf_.capacity())
+    // Fallback value
+    messageSize_ = recvBuf_.capacity();
+
+    if (commsType() == UPstream::commsTypes::nonBlocking)
     {
+        // Non-blocking
+        // ~~~~~~~~~~~~
+        // No chance of probing for size nor relying on the returned message
+        // size (since it returns immediately without any further checks)
+        //
+        // Fortunately there are not many (any?) places that are using
+        // a non-blocking IPstream with streaming anyhow.
+
+        messageSize_ = recvBuf_.size();
+    }
+    else if (!recvBuf_.capacity())
+    {
+        // No buffer size allocated/specified - probe size of incoming message
         profilingPstream::beginTiming();
 
         MPI_Status status;
@@ -212,24 +238,26 @@ void Foam::UIPstream::bufferIPCrecv()
            &status
         );
 
-        MPI_Get_count(&status, MPI_BYTE, &messageSize_);
-
         profilingPstream::addProbeTime();
 
-        recvBuf_.resize(messageSize_);
+        int count(0);
+        MPI_Get_count(&status, MPI_BYTE, &count);
 
         if (UPstream::debug)
         {
             Pout<< "UIPstream::UIPstream : probed size:"
-                << messageSize_ << Foam::endl;
+                << label(count) << Foam::endl;
         }
+
+        recvBuf_.resize(label(count));
+        messageSize_ = label(count);
     }
 
-    messageSize_ = UPstream_mpi_receive
+    std::streamsize count = UPstream_mpi_receive
     (
         commsType(),
         recvBuf_.data(),
-        recvBuf_.capacity(),
+        messageSize_,   // The expected size
         fromProcNo_,
         tag_,
         comm_,
@@ -237,9 +265,10 @@ void Foam::UIPstream::bufferIPCrecv()
     );
 
     // Set addressed size. Leave actual allocated memory intact.
-    recvBuf_.resize(messageSize_);
+    recvBuf_.resize(label(count));
+    messageSize_ = label(count);
 
-    if (!messageSize_)
+    if (recvBuf_.empty())
     {
         setEof();
     }
@@ -248,7 +277,7 @@ void Foam::UIPstream::bufferIPCrecv()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-Foam::label Foam::UIPstream::read
+std::streamsize Foam::UIPstream::read
 (
     const UPstream::commsTypes commsType,
     const int fromProcNo,
diff --git a/src/Pstream/mpi/UOPBstreamWrite.C b/src/Pstream/mpi/UOPBstreamWrite.C
index c01bff64b3..f4c9412fca 100644
--- a/src/Pstream/mpi/UOPBstreamWrite.C
+++ b/src/Pstream/mpi/UOPBstreamWrite.C
@@ -40,7 +40,17 @@ bool Foam::UOPBstream::bufferIPCsend()
     PstreamGlobals::checkCommunicator(comm_, toProcNo_);
 
     // Same type must be expected in UIPBstream::bufferIPCrecv()
-    label bufSize(sendBuf_.size());
+    std::streamsize bufSize(sendBuf_.size());
+
+    // TODO: some corrective action
+    #if 0
+    if (bufSize > std::streamsize(INT_MAX))
+    {
+        Perr<< "UOPBstream::write() :"
+            << " exceeds INT_MAX bytes" << Foam::endl;
+        error::printStack(Perr);
+    }
+    #endif
 
     // Broadcast #1 - data size
     if
@@ -48,7 +58,7 @@ bool Foam::UOPBstream::bufferIPCsend()
         !UPstream::broadcast
         (
             reinterpret_cast<char*>(&bufSize),
-            sizeof(label),
+            sizeof(std::streamsize),
             comm_,
             toProcNo_  //< is actually rootProcNo
         )
@@ -60,26 +70,26 @@ bool Foam::UOPBstream::bufferIPCsend()
         return false;
     }
 
+
     // Broadcast #2 - data content
     // - skip if there is no data to send
-    if (bufSize)
-    {
-        if
+    if
+    (
+        (bufSize > 0)
+     && !UPstream::broadcast
         (
-            !UPstream::broadcast
-            (
-                sendBuf_.data(),
-                sendBuf_.size(),  // same as bufSize
-                comm_,
-                toProcNo_  //< is actually rootProcNo
-            )
+            sendBuf_.data(),
+            sendBuf_.size(),  // same as bufSize
+            comm_,
+            toProcNo_  //< is actually rootProcNo
         )
-        {
-            FatalErrorInFunction
-                << "MPI_Bcast failure sending buffer data:" << bufSize << nl
-                << Foam::abort(FatalError);
-            return false;
-        }
+    )
+    {
+        FatalErrorInFunction
+            << "MPI_Bcast failure sending buffer data:"
+            << sendBuf_.size() << nl
+            << Foam::abort(FatalError);
+        return false;
     }
 
     return true;
diff --git a/src/Pstream/mpi/UOPstreamWrite.C b/src/Pstream/mpi/UOPstreamWrite.C
index c1086fd94c..8613c17dfc 100644
--- a/src/Pstream/mpi/UOPstreamWrite.C
+++ b/src/Pstream/mpi/UOPstreamWrite.C
@@ -62,24 +62,34 @@ bool Foam::UOPstream::write
 {
     PstreamGlobals::reset_request(req);
 
-    if (UPstream::debug)
+    // TODO: some corrective action, at least when not nonBlocking
+    #if 0
+    if (bufSize > std::streamsize(INT_MAX))
     {
-        Pout<< "UOPstream::write : starting write to:" << toProcNo
-            << " tag:" << tag
-            << " comm:" << communicator << " size:" << label(bufSize)
-            << " commType:" << UPstream::commsTypeNames[commsType]
-            << Foam::endl;
+        Perr<< "UOPstream::write() : to rank " << toProcNo
+            << " exceeds INT_MAX bytes" << Foam::endl;
+        error::printStack(Perr);
     }
+    #endif
+
     if (UPstream::warnComm >= 0 && communicator != UPstream::warnComm)
     {
         Pout<< "UOPstream::write : starting write to:" << toProcNo
-            << " tag:" << tag
-            << " comm:" << communicator << " size:" << label(bufSize)
+            << " size:" << label(bufSize)
+            << " tag:" << tag << " comm:" << communicator
             << " commType:" << UPstream::commsTypeNames[commsType]
             << " warnComm:" << UPstream::warnComm
             << Foam::endl;
         error::printStack(Pout);
     }
+    else if (UPstream::debug)
+    {
+        Pout<< "UOPstream::write : starting write to:" << toProcNo
+            << " size:" << label(bufSize)
+            << " tag:" << tag << " comm:" << communicator
+            << " commType:" << UPstream::commsTypeNames[commsType]
+            << Foam::endl;
+    }
 
     PstreamGlobals::checkCommunicator(communicator, toProcNo);
 
@@ -87,7 +97,7 @@ bool Foam::UOPstream::write
 
     profilingPstream::beginTiming();
 
-    if (commsType == UPstream::commsTypes::blocking)
+    if (commsType == UPstream::commsTypes::buffered)
     {
         returnCode = MPI_Bsend
         (
@@ -104,9 +114,9 @@ bool Foam::UOPstream::write
 
         if (UPstream::debug)
         {
-            Pout<< "UOPstream::write : finished write to:" << toProcNo
-                << " tag:" << tag << " size:" << label(bufSize)
-                << " commsType:" << UPstream::commsTypeNames[commsType]
+            Pout<< "UOPstream::write : finished buffered send to:"
+                << toProcNo
+                << " size:" << label(bufSize) << " tag:" << tag
                 << Foam::endl;
         }
     }
@@ -142,9 +152,9 @@ bool Foam::UOPstream::write
 
         if (UPstream::debug)
         {
-            Pout<< "UOPstream::write : finished write to:" << toProcNo
-                << " tag:" << tag << " size:" << label(bufSize)
-                << " commsType:" << UPstream::commsTypeNames[commsType]
+            Pout<< "UOPstream::write : finished send to:"
+                << toProcNo
+                << " size:" << label(bufSize) << " tag:" << tag
                 << Foam::endl;
         }
     }
@@ -181,9 +191,9 @@ bool Foam::UOPstream::write
 
         if (UPstream::debug)
         {
-            Pout<< "UOPstream::write : started write to:" << toProcNo
-                << " tag:" << tag << " size:" << label(bufSize)
-                << " commType:" << UPstream::commsTypeNames[commsType]
+            Pout<< "UOPstream::write : started non-blocking send to:"
+                << toProcNo
+                << " size:" << label(bufSize) << " tag:" << tag
                 << " request:" <<
                 (req ? label(-1) : PstreamGlobals::outstandingRequests_.size())
                 << Foam::endl;
diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index 93bd24cda1..a9f19d3b3f 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -787,7 +787,7 @@ Foam::UPstream::probeMessage
     int flag = 0;
     MPI_Status status;
 
-    if (UPstream::commsTypes::blocking == commsType)
+    if (UPstream::commsTypes::buffered == commsType)
     {
         // Blocking
         profilingPstream::beginTiming();
diff --git a/src/Pstream/mpi/UPstreamBroadcast.C b/src/Pstream/mpi/UPstreamBroadcast.C
index cc75f95ed5..f3b7fac7d4 100644
--- a/src/Pstream/mpi/UPstreamBroadcast.C
+++ b/src/Pstream/mpi/UPstreamBroadcast.C
@@ -47,13 +47,6 @@ bool Foam::UPstream::broadcast
 
     //Needed?  PstreamGlobals::checkCommunicator(comm, rootProcNo);
 
-    if (UPstream::debug)
-    {
-        Pout<< "UPstream::broadcast : root:" << rootProcNo
-            << " comm:" << comm
-            << " size:" << label(bufSize)
-            << Foam::endl;
-    }
     if (UPstream::warnComm >= 0 && comm != UPstream::warnComm)
     {
         Pout<< "UPstream::broadcast : root:" << rootProcNo
@@ -63,6 +56,13 @@ bool Foam::UPstream::broadcast
             << Foam::endl;
         error::printStack(Pout);
     }
+    else if (UPstream::debug)
+    {
+        Pout<< "UPstream::broadcast : root:" << rootProcNo
+            << " comm:" << comm
+            << " size:" << label(bufSize)
+            << Foam::endl;
+    }
 
     profilingPstream::beginTiming();
 
diff --git a/src/Pstream/mpi/UPstreamWrapping.txx b/src/Pstream/mpi/UPstreamWrapping.txx
index db3f095136..94fc3025e1 100644
--- a/src/Pstream/mpi/UPstreamWrapping.txx
+++ b/src/Pstream/mpi/UPstreamWrapping.txx
@@ -632,7 +632,8 @@ void Foam::PstreamDetail::allToAllConsensus
             // Message found, receive into dest buffer location
             const label proci = status.MPI_SOURCE;
 
-            int count = 0;
+            // Only send/recv a single (fundamental) data type
+            int count(0);
             MPI_Get_count(&status, datatype, &count);
 
             if (count != 1)
@@ -812,10 +813,10 @@ void Foam::PstreamDetail::allToAllConsensus
         if (flag)
         {
             // Message found, receive into dest buffer location
-
             const label proci = status.MPI_SOURCE;
-            int count = 0;
 
+            // Only send/recv a single (fundamental) data type
+            int count(0);
             MPI_Get_count(&status, datatype, &count);
 
             if (count != 1)
diff --git a/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/porousBafflePressure/porousBafflePressureFvPatchField.C b/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/porousBafflePressure/porousBafflePressureFvPatchField.C
index 46336accf7..9e56bcb92d 100644
--- a/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/porousBafflePressure/porousBafflePressureFvPatchField.C
+++ b/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/porousBafflePressure/porousBafflePressureFvPatchField.C
@@ -69,7 +69,7 @@ Foam::porousBafflePressureFvPatchField::porousBafflePressureFvPatchField
     {
         if (!this->readValueEntry(dict))
         {
-            this->evaluate(Pstream::commsTypes::blocking);
+            this->evaluate(Pstream::commsTypes::buffered);
         }
     }
 }
diff --git a/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/kqRWallFunctions/kqRWallFunction/kqRWallFunctionFvPatchField.H b/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/kqRWallFunctions/kqRWallFunction/kqRWallFunctionFvPatchField.H
index b552a4cf48..5779218627 100644
--- a/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/kqRWallFunctions/kqRWallFunction/kqRWallFunctionFvPatchField.H
+++ b/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/kqRWallFunctions/kqRWallFunction/kqRWallFunctionFvPatchField.H
@@ -151,7 +151,7 @@ public:
         //- Evaluate the patchField
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/dynamicFaMesh/interfaceTrackingFvMesh/freeSurfacePointDisplacement.C b/src/dynamicFaMesh/interfaceTrackingFvMesh/freeSurfacePointDisplacement.C
index d8d92e959c..8661837cf2 100644
--- a/src/dynamicFaMesh/interfaceTrackingFvMesh/freeSurfacePointDisplacement.C
+++ b/src/dynamicFaMesh/interfaceTrackingFvMesh/freeSurfacePointDisplacement.C
@@ -364,7 +364,7 @@ Foam::interfaceTrackingFvMesh::pointDisplacement()
             {
                 OPstream toNeighbProc
                 (
-                    Pstream::commsTypes::blocking,
+                    Pstream::commsTypes::buffered,
                     procPatch.neighbProcNo()
                 );
 
@@ -375,7 +375,7 @@ Foam::interfaceTrackingFvMesh::pointDisplacement()
             {
                 IPstream fromNeighbProc
                 (
-                    Pstream::commsTypes::blocking,
+                    Pstream::commsTypes::buffered,
                     procPatch.neighbProcNo()
                 );
 
diff --git a/src/dynamicMesh/motionSmoother/motionSmootherAlgo.C b/src/dynamicMesh/motionSmoother/motionSmootherAlgo.C
index ddb61551d5..93d9c97a8a 100644
--- a/src/dynamicMesh/motionSmoother/motionSmootherAlgo.C
+++ b/src/dynamicMesh/motionSmoother/motionSmootherAlgo.C
@@ -587,12 +587,12 @@ void Foam::motionSmootherAlgo::correctBoundaryConditions
             if (schedEval.init)
             {
                 displacementBf[patchi]
-                    .initEvaluate(Pstream::commsTypes::blocking);
+                    .initEvaluate(Pstream::commsTypes::buffered);
             }
             else
             {
                 displacementBf[patchi]
-                    .evaluate(Pstream::commsTypes::blocking);
+                    .evaluate(Pstream::commsTypes::buffered);
             }
         }
     }
@@ -608,12 +608,12 @@ void Foam::motionSmootherAlgo::correctBoundaryConditions
             if (schedEval.init)
             {
                 displacementBf[patchi]
-                    .initEvaluate(Pstream::commsTypes::blocking);
+                    .initEvaluate(Pstream::commsTypes::buffered);
             }
             else
             {
                 displacementBf[patchi]
-                    .evaluate(Pstream::commsTypes::blocking);
+                    .evaluate(Pstream::commsTypes::buffered);
             }
         }
     }
diff --git a/src/dynamicMesh/motionSmoother/motionSmootherAlgoTemplates.C b/src/dynamicMesh/motionSmoother/motionSmootherAlgoTemplates.C
index 98f45bf5be..a38b0a163b 100644
--- a/src/dynamicMesh/motionSmoother/motionSmootherAlgoTemplates.C
+++ b/src/dynamicMesh/motionSmoother/motionSmootherAlgoTemplates.C
@@ -67,12 +67,12 @@ void Foam::motionSmootherAlgo::checkConstraints
 
     forAllReverse(bFld, patchi)
     {
-        bFld[patchi].initEvaluate(Pstream::commsTypes::blocking);   // buffered
+        bFld[patchi].initEvaluate(Pstream::commsTypes::buffered);
     }
 
     forAllReverse(bFld, patchi)
     {
-        bFld[patchi].evaluate(Pstream::commsTypes::blocking);
+        bFld[patchi].evaluate(Pstream::commsTypes::buffered);
     }
 
 
diff --git a/src/finiteArea/faMesh/faBoundaryMesh/faBoundaryMesh.C b/src/finiteArea/faMesh/faBoundaryMesh/faBoundaryMesh.C
index 89c358c1b5..55ee4b2899 100644
--- a/src/finiteArea/faMesh/faBoundaryMesh/faBoundaryMesh.C
+++ b/src/finiteArea/faMesh/faBoundaryMesh/faBoundaryMesh.C
@@ -292,7 +292,7 @@ void Foam::faBoundaryMesh::calcGeometry()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -943,7 +943,7 @@ void Foam::faBoundaryMesh::movePoints(const pointField& p)
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
@@ -989,7 +989,7 @@ void Foam::faBoundaryMesh::updateMesh()
 
     if
     (
-        pBufs.commsType() == Pstream::commsTypes::blocking
+        pBufs.commsType() == Pstream::commsTypes::buffered
      || pBufs.commsType() == Pstream::commsTypes::nonBlocking
     )
     {
diff --git a/src/finiteArea/faMesh/faMeshDemandDrivenData.C b/src/finiteArea/faMesh/faMeshDemandDrivenData.C
index 49b60d4018..66c4bed86d 100644
--- a/src/finiteArea/faMesh/faMeshDemandDrivenData.C
+++ b/src/finiteArea/faMesh/faMeshDemandDrivenData.C
@@ -1606,7 +1606,7 @@ void Foam::faMesh::calcPointAreaNormals(vectorField& result) const
             {
                 UOPstream::write
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     procPatch.neighbProcNo(),
                     patchPointNormals
                 );
@@ -1618,7 +1618,7 @@ void Foam::faMesh::calcPointAreaNormals(vectorField& result) const
             {
                 UIPstream::read
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     procPatch.neighbProcNo(),
                     patchPointNormals
                 );
@@ -1916,7 +1916,7 @@ void Foam::faMesh::calcPointAreaNormalsByQuadricsFit(vectorField& result) const
             {
                 OPstream toNeighbProc
                 (
-                    Pstream::commsTypes::blocking,
+                    Pstream::commsTypes::buffered,
                     procPatch.neighbProcNo(),
                     toNgbProcLsPoints.size_bytes()
                   + toNgbProcLsPointStarts.size_bytes()
@@ -1945,7 +1945,7 @@ void Foam::faMesh::calcPointAreaNormalsByQuadricsFit(vectorField& result) const
             {
                 IPstream fromNeighbProc
                 (
-                    Pstream::commsTypes::blocking,
+                    Pstream::commsTypes::buffered,
                     procPatch.neighbProcNo(),
                     10*patchPointLabels.size()*sizeof(vector)
                   + fromNgbProcLsPointStarts.size_bytes()
diff --git a/src/finiteArea/fields/faPatchFields/basic/basicSymmetry/basicSymmetryFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/basicSymmetry/basicSymmetryFaPatchField.H
index 9772728ab5..8ff67f1b0c 100644
--- a/src/finiteArea/fields/faPatchFields/basic/basicSymmetry/basicSymmetryFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/basicSymmetry/basicSymmetryFaPatchField.H
@@ -130,7 +130,7 @@ public:
             //  HJ, 30/Jun/2009
             virtual void evaluate
             (
-                const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+                const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
             );
 
             //- Return face-gradient transform diagonal
diff --git a/src/finiteArea/fields/faPatchFields/basic/coupled/coupledFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/coupled/coupledFaPatchField.H
index 616d257fe4..e305d5ed9e 100644
--- a/src/finiteArea/fields/faPatchFields/basic/coupled/coupledFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/coupled/coupledFaPatchField.H
@@ -162,7 +162,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {
                 initEvaluate(commsType);
@@ -172,7 +172,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {
                 evaluate(commsType);
diff --git a/src/finiteArea/fields/faPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFaPatchField.H
index 1c618f3f7f..e0c0f8c0c4 100644
--- a/src/finiteArea/fields/faPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFaPatchField.H
@@ -136,7 +136,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/finiteArea/fields/faPatchFields/basic/fixedGradient/fixedGradientFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/fixedGradient/fixedGradientFaPatchField.H
index 760d9668b4..f8156670d3 100644
--- a/src/finiteArea/fields/faPatchFields/basic/fixedGradient/fixedGradientFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/fixedGradient/fixedGradientFaPatchField.H
@@ -210,7 +210,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
 
diff --git a/src/finiteArea/fields/faPatchFields/basic/mixed/mixedFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/mixed/mixedFaPatchField.H
index 16f0e01da0..325136fe19 100644
--- a/src/finiteArea/fields/faPatchFields/basic/mixed/mixedFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/mixed/mixedFaPatchField.H
@@ -231,7 +231,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.H
index 3d31ef2ebe..78a432e81e 100644
--- a/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.H
@@ -178,7 +178,7 @@ public:
             virtual void initEvaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -186,7 +186,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/finiteArea/fields/faPatchFields/basic/zeroGradient/zeroGradientFaPatchField.H b/src/finiteArea/fields/faPatchFields/basic/zeroGradient/zeroGradientFaPatchField.H
index 407c9a9b15..298fd742fc 100644
--- a/src/finiteArea/fields/faPatchFields/basic/zeroGradient/zeroGradientFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/basic/zeroGradient/zeroGradientFaPatchField.H
@@ -133,7 +133,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteArea/fields/faPatchFields/constraint/cyclic/cyclicFaPatchField.C b/src/finiteArea/fields/faPatchFields/constraint/cyclic/cyclicFaPatchField.C
index 70b711375f..7a7812056c 100644
--- a/src/finiteArea/fields/faPatchFields/constraint/cyclic/cyclicFaPatchField.C
+++ b/src/finiteArea/fields/faPatchFields/constraint/cyclic/cyclicFaPatchField.C
@@ -92,7 +92,7 @@ Foam::cyclicFaPatchField<Type>::cyclicFaPatchField
 
     if (IOobjectOption::isReadRequired(requireValue))
     {
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.H b/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.H
index 06736b61b3..e50d5a2a91 100644
--- a/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/constraint/processor/processorFaPatchField.H
@@ -191,7 +191,7 @@ public:
         virtual void initEvaluateLocal
         (
             const Pstream::commsTypes commsType =
-                Pstream::commsTypes::blocking
+                Pstream::commsTypes::buffered
         )
         {}
 
@@ -200,7 +200,7 @@ public:
         virtual void evaluateLocal
         (
             const Pstream::commsTypes commsType =
-                Pstream::commsTypes::blocking
+                Pstream::commsTypes::buffered
         )
         {}
 
diff --git a/src/finiteArea/fields/faPatchFields/constraint/wedge/wedgeFaPatchField.H b/src/finiteArea/fields/faPatchFields/constraint/wedge/wedgeFaPatchField.H
index f417f28c40..22858d7db5 100644
--- a/src/finiteArea/fields/faPatchFields/constraint/wedge/wedgeFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/constraint/wedge/wedgeFaPatchField.H
@@ -124,7 +124,7 @@ public:
             //- Evaluate the patch field
             virtual void evaluate
             (
-                const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+                const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
             );
 
 
diff --git a/src/finiteArea/fields/faPatchFields/derived/clampedPlate/clampedPlateFaPatchField.H b/src/finiteArea/fields/faPatchFields/derived/clampedPlate/clampedPlateFaPatchField.H
index ca38463e02..1fd9007a83 100644
--- a/src/finiteArea/fields/faPatchFields/derived/clampedPlate/clampedPlateFaPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/derived/clampedPlate/clampedPlateFaPatchField.H
@@ -155,7 +155,7 @@ public:
             //- Evaluate the patch field
             virtual void evaluate
             (
-                const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+                const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteArea/fields/faPatchFields/faPatchField/faPatchField.H b/src/finiteArea/fields/faPatchFields/faPatchField/faPatchField.H
index e99ab8dae0..0c47bd2ceb 100644
--- a/src/finiteArea/fields/faPatchFields/faPatchField/faPatchField.H
+++ b/src/finiteArea/fields/faPatchFields/faPatchField/faPatchField.H
@@ -564,7 +564,7 @@ public:
             virtual void initEvaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -572,7 +572,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Initialise the evaluation of the patch field after a local
@@ -580,7 +580,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -588,7 +588,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/finiteArea/fields/faePatchFields/faePatchField/faePatchField.H b/src/finiteArea/fields/faePatchFields/faePatchField/faePatchField.H
index fd1c318d8e..bf487edd2d 100644
--- a/src/finiteArea/fields/faePatchFields/faePatchField/faePatchField.H
+++ b/src/finiteArea/fields/faePatchFields/faePatchField/faePatchField.H
@@ -482,7 +482,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -490,7 +490,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -516,14 +516,14 @@ public:
         //- Initialise the evaluation of the patch field, generally a no-op
         virtual void initEvaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         )
         {}
 
         //- Evaluate the patch field, generally a no-op
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         )
         {}
 
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H
index 9c9fabaf73..30d2268cfd 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H
@@ -125,7 +125,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/coupled/coupledFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/coupled/coupledFvPatchField.H
index 23ff2481f5..60671c45dc 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/coupled/coupledFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/coupled/coupledFvPatchField.H
@@ -188,7 +188,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {
                 initEvaluate(commsType);
@@ -198,7 +198,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {
                 evaluate(commsType);
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/directionMixed/directionMixedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/directionMixed/directionMixedFvPatchField.H
index effa2031c7..b4b5e3060d 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/directionMixed/directionMixedFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/directionMixed/directionMixedFvPatchField.H
@@ -191,7 +191,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFvPatchField.H
index a18da2822a..84c9f30f8c 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/extrapolatedCalculated/extrapolatedCalculatedFvPatchField.H
@@ -135,7 +135,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 };
 
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/fixedGradient/fixedGradientFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/fixedGradient/fixedGradientFvPatchField.H
index f80fadc4fe..07919120ba 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/fixedGradient/fixedGradientFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/fixedGradient/fixedGradientFvPatchField.H
@@ -210,7 +210,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/mixed/mixedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/mixed/mixedFvPatchField.H
index 7d4f5518f7..67d8b9ac7a 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/mixed/mixedFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/mixed/mixedFvPatchField.H
@@ -268,7 +268,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.H
index cb2f0797ac..0c9f707d4c 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.H
@@ -176,7 +176,7 @@ public:
             virtual void initEvaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -184,7 +184,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/zeroGradient/zeroGradientFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/basic/zeroGradient/zeroGradientFvPatchField.H
index 094fe5b625..950b8b2ecf 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/zeroGradient/zeroGradientFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/basic/zeroGradient/zeroGradientFvPatchField.H
@@ -142,7 +142,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return the matrix diagonal coefficients corresponding to the
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/cyclic/cyclicFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/constraint/cyclic/cyclicFvPatchField.C
index 7a70acb1e0..380b6e4999 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/cyclic/cyclicFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/cyclic/cyclicFvPatchField.C
@@ -70,7 +70,7 @@ Foam::cyclicFvPatchField<Type>::cyclicFvPatchField
 
     if (needValue)
     {
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/cyclicACMI/cyclicACMIFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/constraint/cyclicACMI/cyclicACMIFvPatchField.C
index f287734adc..a95239a9b6 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/cyclicACMI/cyclicACMIFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/cyclicACMI/cyclicACMIFvPatchField.C
@@ -121,7 +121,7 @@ Foam::cyclicACMIFvPatchField<Type>::cyclicACMIFvPatchField
         const int oldConsistency = consistency;
         consistency = 0;
 
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
 
         consistency = oldConsistency;
     }
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/jumpCyclicAMI/jumpCyclicAMIFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/constraint/jumpCyclicAMI/jumpCyclicAMIFvPatchField.C
index dcd345fc87..fad9173a2e 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/jumpCyclicAMI/jumpCyclicAMIFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/jumpCyclicAMI/jumpCyclicAMIFvPatchField.C
@@ -66,7 +66,7 @@ Foam::jumpCyclicAMIFvPatchField<Type>::jumpCyclicAMIFvPatchField
     cyclicAMIFvPatchField<Type>(p, iF, dict)
 {
     // Call this evaluation in derived classes
-    //this->evaluate(Pstream::commsTypes::blocking);
+    //this->evaluate(Pstream::commsTypes::buffered);
 }
 
 
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/processor/processorFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/constraint/processor/processorFvPatchField.H
index 08b110dc81..9cf3b074a5 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/processor/processorFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/processor/processorFvPatchField.H
@@ -199,7 +199,7 @@ public:
         virtual void initEvaluateLocal
         (
             const Pstream::commsTypes commsType =
-                Pstream::commsTypes::blocking
+                Pstream::commsTypes::buffered
         )
         {}
 
@@ -208,7 +208,7 @@ public:
         virtual void evaluateLocal
         (
             const Pstream::commsTypes commsType =
-                Pstream::commsTypes::blocking
+                Pstream::commsTypes::buffered
         )
         {}
 
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/symmetryPlane/symmetryPlaneFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/constraint/symmetryPlane/symmetryPlaneFvPatchField.H
index 400112d67a..5ea077b08a 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/symmetryPlane/symmetryPlaneFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/symmetryPlane/symmetryPlaneFvPatchField.H
@@ -145,7 +145,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/constraint/wedge/wedgeFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/constraint/wedge/wedgeFvPatchField.H
index 6d8e34e98b..fe9e31f644 100644
--- a/src/finiteVolume/fields/fvPatchFields/constraint/wedge/wedgeFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/constraint/wedge/wedgeFvPatchField.H
@@ -146,7 +146,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.C
index eaf2de2de4..64926a0bae 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.C
@@ -192,7 +192,7 @@ Foam::codedFixedValueFvPatchField<Type>::codedFixedValueFvPatchField
         this->extrapolateInternal();
 
         // Evaluate to assign a value
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.H
index 3cde2e1c53..425208697f 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/codedFixedValue/codedFixedValueFvPatchField.H
@@ -245,7 +245,7 @@ public:
         //- Evaluate the patch field, sets updated() to false
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/codedMixed/codedMixedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/codedMixed/codedMixedFvPatchField.H
index 863bd67ffb..b02036e92d 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/codedMixed/codedMixedFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/codedMixed/codedMixedFvPatchField.H
@@ -251,7 +251,7 @@ public:
         //  to false.
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/fan/fanFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/fan/fanFvPatchField.C
index 921199406e..107fcf30a5 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/fan/fanFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/fan/fanFvPatchField.C
@@ -89,7 +89,7 @@ Foam::fanFvPatchField<Type>::fanFvPatchField
 
     if (!this->readValueEntry(dict))
     {
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/fixedJump/fixedJumpFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/fixedJump/fixedJumpFvPatchField.C
index 8d62f14c27..4eafe72c8c 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/fixedJump/fixedJumpFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/fixedJump/fixedJumpFvPatchField.C
@@ -94,7 +94,7 @@ Foam::fixedJumpFvPatchField<Type>::fixedJumpFvPatchField
     {
         if (!this->readValueEntry(dict))
         {
-            this->evaluate(Pstream::commsTypes::blocking);
+            this->evaluate(Pstream::commsTypes::buffered);
         }
     }
 }
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/fixedJumpAMI/fixedJumpAMIFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/fixedJumpAMI/fixedJumpAMIFvPatchField.C
index b3efdea596..4c8c5aa199 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/fixedJumpAMI/fixedJumpAMIFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/fixedJumpAMI/fixedJumpAMIFvPatchField.C
@@ -73,7 +73,7 @@ Foam::fixedJumpAMIFvPatchField<Type>::fixedJumpAMIFvPatchField
 
     if (!this->readValueEntry(dict))
     {
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/fixedNormalSlip/fixedNormalSlipFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/fixedNormalSlip/fixedNormalSlipFvPatchField.H
index 8fdfb7e7fd..026a245ccb 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/fixedNormalSlip/fixedNormalSlipFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/fixedNormalSlip/fixedNormalSlipFvPatchField.H
@@ -219,7 +219,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.C b/src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.C
index 156ce0376b..bc4504b4a5 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.C
@@ -93,7 +93,7 @@ flowRateInletVelocityFvPatchVectorField
     // Value field required if mass based
     if (!this->readValueEntry(dict))
     {
-        evaluate(Pstream::commsTypes::blocking);
+        evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/flowRateOutletVelocity/flowRateOutletVelocityFvPatchVectorField.C b/src/finiteVolume/fields/fvPatchFields/derived/flowRateOutletVelocity/flowRateOutletVelocityFvPatchVectorField.C
index 045f59e00f..7ff807b21a 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/flowRateOutletVelocity/flowRateOutletVelocityFvPatchVectorField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/flowRateOutletVelocity/flowRateOutletVelocityFvPatchVectorField.C
@@ -87,7 +87,7 @@ flowRateOutletVelocityFvPatchVectorField
     // Value field required if mass based
     if (!this->readValueEntry(dict))
     {
-        evaluate(Pstream::commsTypes::blocking);
+        evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/fluxCorrectedVelocity/fluxCorrectedVelocityFvPatchVectorField.H b/src/finiteVolume/fields/fvPatchFields/derived/fluxCorrectedVelocity/fluxCorrectedVelocityFvPatchVectorField.H
index 3756b435a7..6a9f71ede2 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/fluxCorrectedVelocity/fluxCorrectedVelocityFvPatchVectorField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/fluxCorrectedVelocity/fluxCorrectedVelocityFvPatchVectorField.H
@@ -168,7 +168,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/matchedFlowRateOutletVelocity/matchedFlowRateOutletVelocityFvPatchVectorField.C b/src/finiteVolume/fields/fvPatchFields/derived/matchedFlowRateOutletVelocity/matchedFlowRateOutletVelocityFvPatchVectorField.C
index 2b895940b7..e407d0ec07 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/matchedFlowRateOutletVelocity/matchedFlowRateOutletVelocityFvPatchVectorField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/matchedFlowRateOutletVelocity/matchedFlowRateOutletVelocityFvPatchVectorField.C
@@ -72,7 +72,7 @@ matchedFlowRateOutletVelocityFvPatchVectorField
     // Value field required if mass based
     if (!this->readValueEntry(dict))
     {
-        evaluate(Pstream::commsTypes::blocking);
+        evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/partialSlip/partialSlipFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/partialSlip/partialSlipFvPatchField.H
index a81ce92912..4858f5ba96 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/partialSlip/partialSlipFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/partialSlip/partialSlipFvPatchField.H
@@ -215,7 +215,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Return face-gradient transform diagonal
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValueFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValueFvPatchField.C
index 8491516dab..40dc0780cc 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValueFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValueFvPatchField.C
@@ -72,7 +72,7 @@ timeVaryingMappedFixedValueFvPatchField
         //       by re-setting of fvatchfield::updated_ flag. This is
         //       so if first use is in the next time step it retriggers
         //       a new update.
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/uniformJump/uniformJumpFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/uniformJump/uniformJumpFvPatchField.C
index deca4b4732..a10457eea4 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/uniformJump/uniformJumpFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/uniformJump/uniformJumpFvPatchField.C
@@ -77,7 +77,7 @@ Foam::uniformJumpFvPatchField<Type>::uniformJumpFvPatchField
 
         if (!this->readValueEntry(dict))
         {
-            this->evaluate(Pstream::commsTypes::blocking);
+            this->evaluate(Pstream::commsTypes::buffered);
         }
     }
 }
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/uniformJumpAMI/uniformJumpAMIFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/uniformJumpAMI/uniformJumpAMIFvPatchField.C
index c0bf9569a7..07be85db27 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/uniformJumpAMI/uniformJumpAMIFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/uniformJumpAMI/uniformJumpAMIFvPatchField.C
@@ -74,7 +74,7 @@ Foam::uniformJumpAMIFvPatchField<Type>::uniformJumpAMIFvPatchField
 
     if (!this->readValueEntry(dict))
     {
-        this->evaluate(Pstream::commsTypes::blocking);
+        this->evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/finiteVolume/fields/fvPatchFields/fvPatchField/fvPatchField.H b/src/finiteVolume/fields/fvPatchFields/fvPatchField/fvPatchField.H
index 993433fd61..5acccdf4d0 100644
--- a/src/finiteVolume/fields/fvPatchFields/fvPatchField/fvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/fvPatchField/fvPatchField.H
@@ -635,7 +635,7 @@ public:
             virtual void initEvaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -643,7 +643,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             );
 
             //- Initialise the evaluation of the patch field after a local
@@ -651,7 +651,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -659,7 +659,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/finiteVolume/fields/fvsPatchFields/fvsPatchField/fvsPatchField.H b/src/finiteVolume/fields/fvsPatchFields/fvsPatchField/fvsPatchField.H
index ddb7dfa8b6..63cc9f794c 100644
--- a/src/finiteVolume/fields/fvsPatchFields/fvsPatchField/fvsPatchField.H
+++ b/src/finiteVolume/fields/fvsPatchFields/fvsPatchField/fvsPatchField.H
@@ -511,7 +511,7 @@ public:
             virtual void initEvaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -519,7 +519,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -528,7 +528,7 @@ public:
             virtual void initEvaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
@@ -536,7 +536,7 @@ public:
             virtual void evaluateLocal
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/functionObjects/field/mapFields/mapFieldsTemplates.C b/src/functionObjects/field/mapFields/mapFieldsTemplates.C
index 749def67a3..2350ef32c0 100644
--- a/src/functionObjects/field/mapFields/mapFieldsTemplates.C
+++ b/src/functionObjects/field/mapFields/mapFieldsTemplates.C
@@ -43,7 +43,7 @@ void Foam::functionObjects::mapFields::evaluateConstraintTypes
 
     if
     (
-        commsType == UPstream::commsTypes::blocking
+        commsType == UPstream::commsTypes::buffered
      || commsType == UPstream::commsTypes::nonBlocking
     )
     {
diff --git a/src/fvMotionSolver/pointPatchFields/derived/surfaceSlipDisplacement/surfaceSlipDisplacementPointPatchVectorField.H b/src/fvMotionSolver/pointPatchFields/derived/surfaceSlipDisplacement/surfaceSlipDisplacementPointPatchVectorField.H
index 8fa5889ebe..a65d3d7910 100644
--- a/src/fvMotionSolver/pointPatchFields/derived/surfaceSlipDisplacement/surfaceSlipDisplacementPointPatchVectorField.H
+++ b/src/fvMotionSolver/pointPatchFields/derived/surfaceSlipDisplacement/surfaceSlipDisplacementPointPatchVectorField.H
@@ -190,7 +190,7 @@ public:
         //- Update the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write
diff --git a/src/fvMotionSolver/pointPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValuePointPatchField.C b/src/fvMotionSolver/pointPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValuePointPatchField.C
index e2475907e1..73f8923439 100644
--- a/src/fvMotionSolver/pointPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValuePointPatchField.C
+++ b/src/fvMotionSolver/pointPatchFields/derived/timeVaryingMappedFixedValue/timeVaryingMappedFixedValuePointPatchField.C
@@ -107,7 +107,7 @@ timeVaryingMappedFixedValuePointPatchField
         //       of the pointPatchField::updated_ flag. This is
         //       so if first use is in the next time step it retriggers
         //       a new update.
-        pointPatchField<Type>::evaluate(Pstream::commsTypes::blocking);
+        pointPatchField<Type>::evaluate(Pstream::commsTypes::buffered);
     }
 }
 
diff --git a/src/meshTools/AMIInterpolation/patches/cyclicACMI/cyclicACMIPointPatchField/cyclicACMIPointPatchField.H b/src/meshTools/AMIInterpolation/patches/cyclicACMI/cyclicACMIPointPatchField/cyclicACMIPointPatchField.H
index 6c618a9747..2dd4ed08e4 100644
--- a/src/meshTools/AMIInterpolation/patches/cyclicACMI/cyclicACMIPointPatchField/cyclicACMIPointPatchField.H
+++ b/src/meshTools/AMIInterpolation/patches/cyclicACMI/cyclicACMIPointPatchField/cyclicACMIPointPatchField.H
@@ -199,7 +199,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/meshTools/AMIInterpolation/patches/cyclicAMI/cyclicAMIPointPatchField/cyclicAMIPointPatchField.H b/src/meshTools/AMIInterpolation/patches/cyclicAMI/cyclicAMIPointPatchField/cyclicAMIPointPatchField.H
index f6ffa116bb..35816cc5ac 100644
--- a/src/meshTools/AMIInterpolation/patches/cyclicAMI/cyclicAMIPointPatchField/cyclicAMIPointPatchField.H
+++ b/src/meshTools/AMIInterpolation/patches/cyclicAMI/cyclicAMIPointPatchField/cyclicAMIPointPatchField.H
@@ -203,7 +203,7 @@ public:
             virtual void evaluate
             (
                 const Pstream::commsTypes commsType =
-                    Pstream::commsTypes::blocking
+                    Pstream::commsTypes::buffered
             )
             {}
 
diff --git a/src/optimisation/adjointOptimisation/adjoint/adjointBoundaryConditions/adjointOutletVelocity/adjointOutletVelocityFvPatchVectorField.H b/src/optimisation/adjointOptimisation/adjoint/adjointBoundaryConditions/adjointOutletVelocity/adjointOutletVelocityFvPatchVectorField.H
index 1932066698..9b8d6cd1e6 100644
--- a/src/optimisation/adjointOptimisation/adjoint/adjointBoundaryConditions/adjointOutletVelocity/adjointOutletVelocityFvPatchVectorField.H
+++ b/src/optimisation/adjointOptimisation/adjoint/adjointBoundaryConditions/adjointOutletVelocity/adjointOutletVelocityFvPatchVectorField.H
@@ -138,7 +138,7 @@ public:
         //  adjoint pressure BC
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType = Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType = Pstream::commsTypes::buffered
         );
 
         //virtual void updateCoeffs();
diff --git a/src/sampling/surface/isoSurface/isoSurfacePoint.C b/src/sampling/surface/isoSurface/isoSurfacePoint.C
index 0de39dbcd6..020a0465a2 100644
--- a/src/sampling/surface/isoSurface/isoSurfacePoint.C
+++ b/src/sampling/surface/isoSurface/isoSurfacePoint.C
@@ -164,10 +164,9 @@ void Foam::isoSurfacePoint::syncUnseparatedPoints
                     patchInfo[nbrPointi] = pointValues[meshPts[pointi]];
                 }
 
-                // buffered send
                 OPstream toNbr
                 (
-                    UPstream::commsTypes::blocking,
+                    UPstream::commsTypes::buffered,
                     procPatch.neighbProcNo()
                 );
                 toNbr << patchInfo;
diff --git a/src/surfMesh/writers/debug/debugSurfaceWriter.H b/src/surfMesh/writers/debug/debugSurfaceWriter.H
index 239f4be28c..bbe5c4fca6 100644
--- a/src/surfMesh/writers/debug/debugSurfaceWriter.H
+++ b/src/surfMesh/writers/debug/debugSurfaceWriter.H
@@ -44,7 +44,7 @@ Description
     Format options:
     \table
         Property    | Description                           | Required | Default
-        commsType   | blocking/nonBlocking/scheduled        | no  | scheduled
+        commsType   | scheduled/nonBlocking/buffered        | no  | scheduled
         merge       | Enable geometry/field merging         | no  | true
         write       | Write file(s)                         | no  | false
     \endtable
diff --git a/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJump/energyJumpFvPatchScalarField.C b/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJump/energyJumpFvPatchScalarField.C
index c7bf081805..d2beacf925 100644
--- a/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJump/energyJumpFvPatchScalarField.C
+++ b/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJump/energyJumpFvPatchScalarField.C
@@ -66,7 +66,7 @@ Foam::energyJumpFvPatchScalarField::energyJumpFvPatchScalarField
 {
     if (!this->readValueEntry(dict))
     {
-        evaluate(Pstream::commsTypes::blocking);
+        evaluate(Pstream::commsTypes::buffered);
     }
 }
 
@@ -115,7 +115,7 @@ void Foam::energyJumpFvPatchScalarField::updateCoeffs()
             const_cast<fixedJumpFvPatchScalarField&>(TbPatch);
 
         // force update of jump
-        Tbp.evaluate(Pstream::commsTypes::blocking);
+        Tbp.evaluate(Pstream::commsTypes::buffered);
 
         const labelUList& faceCells = this->patch().faceCells();
 
diff --git a/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJumpAMI/energyJumpAMIFvPatchScalarField.C b/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJumpAMI/energyJumpAMIFvPatchScalarField.C
index 8a55c2152d..d222d40dd8 100644
--- a/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJumpAMI/energyJumpAMIFvPatchScalarField.C
+++ b/src/thermophysicalModels/basic/derivedFvPatchFields/energyJump/energyJumpAMI/energyJumpAMIFvPatchScalarField.C
@@ -66,7 +66,7 @@ Foam::energyJumpAMIFvPatchScalarField::energyJumpAMIFvPatchScalarField
 {
     if (!this->readValueEntry(dict))
     {
-        evaluate(Pstream::commsTypes::blocking);
+        evaluate(Pstream::commsTypes::buffered);
     }
 }
 
@@ -115,7 +115,7 @@ void Foam::energyJumpAMIFvPatchScalarField::updateCoeffs()
             const_cast<fixedJumpAMIFvPatchScalarField&>(TbPatch);
 
         // force update of jump
-        Tbp.evaluate(Pstream::commsTypes::blocking);
+        Tbp.evaluate(Pstream::commsTypes::buffered);
 
         const labelUList& faceCells = this->patch().faceCells();
 
diff --git a/src/transportModels/interfaceProperties/alphaContactAngle/alphaContactAngleTwoPhaseFvPatchScalarField.H b/src/transportModels/interfaceProperties/alphaContactAngle/alphaContactAngleTwoPhaseFvPatchScalarField.H
index 12cff614f1..d9fe5dca2e 100644
--- a/src/transportModels/interfaceProperties/alphaContactAngle/alphaContactAngleTwoPhaseFvPatchScalarField.H
+++ b/src/transportModels/interfaceProperties/alphaContactAngle/alphaContactAngleTwoPhaseFvPatchScalarField.H
@@ -148,7 +148,7 @@ public:
         //- Evaluate the patch field
         virtual void evaluate
         (
-            const Pstream::commsTypes commsType=Pstream::commsTypes::blocking
+            const Pstream::commsTypes commsType=Pstream::commsTypes::buffered
         );
 
         //- Write