diff --git a/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.C b/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.C
index d2a3ca2c2..df79d50c0 100644
--- a/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.C
+++ b/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.C
@@ -50,12 +50,6 @@ Foam::twoPhaseMixtureThermo::twoPhaseMixtureThermo
     thermo1_(nullptr),
     thermo2_(nullptr)
 {
-    // Note: we're writing files to be read in immediately afterwards.
-    //       Avoid any thread-writing problems.
-    float bufSz =
-        fileOperations::collatedFileOperation::maxThreadFileBufferSize;
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
     {
         volScalarField T1
         (
@@ -86,9 +80,9 @@ Foam::twoPhaseMixtureThermo::twoPhaseMixtureThermo
         T2.write();
     }
 
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize =
-        bufSz;
-
+    // Note: we're writing files to be read in immediately afterwards.
+    //       Avoid any thread-writing problems.
+    fileHandler().flush();
 
     thermo1_ = rhoThermo::New(U.mesh(), phase1Name());
     thermo2_ = rhoThermo::New(U.mesh(), phase2Name());
diff --git a/applications/utilities/mesh/manipulation/setSet/setSet.C b/applications/utilities/mesh/manipulation/setSet/setSet.C
index f425a201f..70d8d3bc8 100644
--- a/applications/utilities/mesh/manipulation/setSet/setSet.C
+++ b/applications/utilities/mesh/manipulation/setSet/setSet.C
@@ -48,7 +48,6 @@ Description
 #include "faceZoneSet.H"
 #include "pointZoneSet.H"
 #include "timeSelector.H"
-#include "collatedFileOperation.H"
 
 #include <stdio.h>
 
@@ -349,6 +348,8 @@ void removeZone
         zones.setSize(zones.size()-1);
         zones.clearAddressing();
         zones.write();
+        // Force flushing so we know it has finished writing
+        fileHandler().flush();
     }
 }
 
@@ -603,6 +604,8 @@ bool doCommand
                     currentSet.instance() = mesh.time().timeName();
                 }
                 currentSet.write();
+                // Make sure writing is finished
+                fileHandler().flush();
             }
         }
     }
@@ -809,8 +812,6 @@ int main(int argc, char *argv[])
     // Specific to topoSet/setSet: quite often we want to block upon writing
     // a set so we can immediately re-read it. So avoid use of threading
     // for set writing.
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
     timeSelector::addOptions(true, false);
     #include "addRegionOption.H"
     argList::addBoolOption("noVTK", "do not write VTK files");
diff --git a/applications/utilities/mesh/manipulation/topoSet/topoSet.C b/applications/utilities/mesh/manipulation/topoSet/topoSet.C
index e4aa0eb77..10e1718fb 100644
--- a/applications/utilities/mesh/manipulation/topoSet/topoSet.C
+++ b/applications/utilities/mesh/manipulation/topoSet/topoSet.C
@@ -40,7 +40,6 @@ Description
 #include "faceZoneSet.H"
 #include "pointZoneSet.H"
 #include "IOdictionary.H"
-#include "collatedFileOperation.H"
 
 using namespace Foam;
 
@@ -85,6 +84,7 @@ void removeZone
         zones.setSize(zones.size()-1);
         zones.clearAddressing();
         zones.write();
+        fileHandler().flush();
     }
 }
 
@@ -193,11 +193,6 @@ polyMesh::readUpdateState meshReadUpdate(polyMesh& mesh)
 
 int main(int argc, char *argv[])
 {
-    // Specific to topoSet/setSet: quite often we want to block upon writing
-    // a set so we can immediately re-read it. So avoid use of threading
-    // for set writing.
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
     timeSelector::addOptions(true, false);
     #include "addDictOption.H"
     #include "addRegionOption.H"
@@ -302,6 +297,7 @@ int main(int argc, char *argv[])
                     // Synchronize for coupled patches.
                     if (!noSync) currentSet().sync(mesh);
                     currentSet().write();
+                    fileHandler().flush();
                 }
                 break;
 
@@ -336,6 +332,7 @@ int main(int argc, char *argv[])
                     // Synchronize for coupled patches.
                     if (!noSync) currentSet().sync(mesh);
                     currentSet().write();
+                    fileHandler().flush();
                 }
                 break;
 
@@ -343,12 +340,14 @@ int main(int argc, char *argv[])
                     Info<< "    Clearing " << currentSet().type() << endl;
                     currentSet().clear();
                     currentSet().write();
+                    fileHandler().flush();
                 break;
 
                 case topoSetSource::INVERT:
                     Info<< "    Inverting " << currentSet().type() << endl;
                     currentSet().invert(currentSet().maxSize(mesh));
                     currentSet().write();
+                    fileHandler().flush();
                 break;
 
                 case topoSetSource::REMOVE:
diff --git a/applications/utilities/parallelProcessing/decomposePar/decomposePar.C b/applications/utilities/parallelProcessing/decomposePar/decomposePar.C
index 92e2950f5..642e8ccb8 100644
--- a/applications/utilities/parallelProcessing/decomposePar/decomposePar.C
+++ b/applications/utilities/parallelProcessing/decomposePar/decomposePar.C
@@ -104,7 +104,6 @@ Usage
 #include "pointFieldDecomposer.H"
 #include "lagrangianFieldDecomposer.H"
 #include "decompositionModel.H"
-#include "collatedFileOperation.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -459,12 +458,6 @@ int main(int argc, char *argv[])
         // Decompose the mesh
         if (!decomposeFieldsOnly)
         {
-            // Disable buffering when writing mesh since we need to read
-            // it later on when decomposing the fields
-            float bufSz =
-                fileOperations::collatedFileOperation::maxThreadFileBufferSize;
-            fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
             mesh.decomposeMesh(dictIO.objectPath());
 
             mesh.writeDecomposition(decomposeSets);
@@ -521,8 +514,7 @@ int main(int argc, char *argv[])
                     << endl;
             }
 
-            fileOperations::collatedFileOperation::maxThreadFileBufferSize =
-                bufSz;
+            fileHandler().flush();
         }
 
 
diff --git a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoam.C b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoam.C
index 6a24a189c..684fab66d 100644
--- a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoam.C
+++ b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoam.C
@@ -97,7 +97,8 @@ int Foam::vtkPVFoam::setTime(int nRequest, const double requestTimes[])
 {
     Time& runTime = dbPtr_();
 
-    // Get times list
+    // Get times list. Flush first to force refresh.
+    fileHandler().flush();
     instantList Times = runTime.times();
 
     int nearestIndex = timeIndex_;
@@ -248,11 +249,6 @@ Foam::vtkPVFoam::vtkPVFoam
 
     fileName FileName(vtkFileName);
 
-    // Make sure not to use the threaded version - it does not like
-    // being loaded as a shared library - static cleanup order is problematic.
-    // For now just disable the threaded writer.
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
     // avoid argList and get rootPath/caseName directly from the file
     fileName fullCasePath(FileName.path());
 
@@ -575,6 +571,8 @@ double* Foam::vtkPVFoam::findTimes(int& nTimeSteps)
     if (dbPtr_.valid())
     {
         Time& runTime = dbPtr_();
+        // Get times list. Flush first to force refresh.
+        fileHandler().flush();
         instantList timeLst = runTime.times();
 
         // find the first time for which this mesh appears to exist
diff --git a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoamUpdateInfo.C b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoamUpdateInfo.C
index 2f1c0add6..dba80d9a0 100644
--- a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoamUpdateInfo.C
+++ b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoamUpdateInfo.C
@@ -192,6 +192,9 @@ void Foam::vtkPVFoam::updateInfoLagrangian
 
     // Generate a list of lagrangian clouds across all times
     HashSet<fileName> cloudDirs;
+
+    // Get times list. Flush first to force refresh.
+    fileHandler().flush();
     instantList times = dbPtr_().times();
     forAll(times, timei)
     {
@@ -706,6 +709,8 @@ void Foam::vtkPVFoam::updateInfoLagrangianFields()
     // set. ParaView will display "(partial)" after field names that only apply
     // to some of the clouds.
     const arrayRange& range = arrayRangeLagrangian_;
+
+    fileHandler().flush();
     for (label partId = range.start(); partId < range.end(); ++ partId)
     {
         const instantList times = dbPtr_().times();
diff --git a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVblockMesh/vtkPVblockMesh.C b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVblockMesh/vtkPVblockMesh.C
index d79398601..69b76444b 100644
--- a/applications/utilities/postProcessing/graphics/PVReaders/vtkPVblockMesh/vtkPVblockMesh.C
+++ b/applications/utilities/postProcessing/graphics/PVReaders/vtkPVblockMesh/vtkPVblockMesh.C
@@ -31,7 +31,6 @@ License
 #include "Time.H"
 #include "patchZones.H"
 #include "OStringStream.H"
-#include "collatedFileOperation.H"
 
 // VTK includes
 #include "vtkDataArraySelection.h"
@@ -171,12 +170,6 @@ Foam::vtkPVblockMesh::vtkPVblockMesh
             << FileName << endl;
     }
 
-    // Make sure not to use the threaded version - it does not like
-    // being loaded as a shared library - static cleanup order is problematic.
-    // For now just disable the threaded writer.
-    fileOperations::collatedFileOperation::maxThreadFileBufferSize = 0;
-
-
     // avoid argList and get rootPath/caseName directly from the file
     fileName fullCasePath(fileName(FileName).path());
 
diff --git a/etc/controlDict b/etc/controlDict
index d927ea413..4179091ae 100644
--- a/etc/controlDict
+++ b/etc/controlDict
@@ -58,7 +58,7 @@ OptimisationSwitches
 
     //- Parallel IO file handler
     //  uncollated (default), collated or masterUncollated
-    fileHandler uncollated;
+    fileHandler collated;
 
     //- collated: thread buffer size for queued file writes.
     //  If set to 0 or not sufficient for the file size threading is not used.
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
index 614e846af..5abaf3c70 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
@@ -608,6 +608,18 @@ bool Foam::fileOperations::collatedFileOperation::writeObject
     }
 }
 
+void Foam::fileOperations::collatedFileOperation::flush() const
+{
+    if (debug)
+    {
+        Pout<< "collatedFileOperation::flush : clearing and waiting for thread"
+            << endl;
+    }
+    masterUncollatedFileOperation::flush();
+    // Wait for thread to finish (note: also removes thread)
+    writer_.waitAll();
+}
+
 
 Foam::word Foam::fileOperations::collatedFileOperation::processorsDir
 (
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
index f1acda477..4e65454ce 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
@@ -155,6 +155,9 @@ public:
 
         // Other
 
+            //- Forcibly wait until all output done. Flush any cached data
+            virtual void flush() const;
+
             //- Actual name of processors dir
             virtual word processorsDir(const IOobject&) const;
 
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index 8c8640ff0..65b39843d 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -982,6 +982,17 @@ Foam::label Foam::fileOperation::nProcs
 }
 
 
+void Foam::fileOperation::flush() const
+{
+    if (debug)
+    {
+        Pout<< "fileOperation::flush : clearing processor directories cache"
+            << endl;
+    }
+    procsDirs_.clear();
+}
+
+
 Foam::fileName Foam::fileOperation::processorsCasePath
 (
     const IOobject& io,
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index 2ea2832a7..84c928b57 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -485,6 +485,9 @@ public:
             virtual void setTime(const Time&) const
             {}
 
+            //- Forcibly wait until all output done. Flush any cached data
+            virtual void flush() const;
+
             //- Generate path (like io.path) from root+casename with any
             //  'processorXXX' replaced by procDir (usually 'processsors')
             fileName processorsCasePath
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index 25fc3c811..0f0675e30 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -2532,6 +2532,13 @@ Foam::fileOperations::masterUncollatedFileOperation::NewOFstream
 }
 
 
+void Foam::fileOperations::masterUncollatedFileOperation::flush() const
+{
+    fileOperation::flush();
+    times_.clear();
+}
+
+
 Foam::label Foam::fileOperations::masterUncollatedFileOperation::addWatch
 (
     const fileName& fName
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
index 15ee260a0..93862fc2a 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
@@ -752,6 +752,9 @@ public:
             //- Callback for time change
             virtual void setTime(const Time&) const;
 
+            //- Forcibly wait until all output done. Flush any cached data
+            virtual void flush() const;
+
             //- Return cached times
             const HashPtrTable<instantList>& times() const
             {