From 5f1a8f824bfb4458d5002396c88d911e6c568968 Mon Sep 17 00:00:00 2001
From: Henry Weller <http://openfoam.org>
Date: Fri, 7 Jul 2017 20:49:53 +0100
Subject: [PATCH] fileHandler::collatedFileOperation: Added useful message
 concerning threading control

---
 .../collatedFileOperation.C                   | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
index 0984b675f..b5dbb1351 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
@@ -183,6 +183,27 @@ Foam::fileOperations::collatedFileOperation::collatedFileOperation
         Info<< "I/O    : " << typeName
             << " (maxThreadFileBufferSize " << maxThreadFileBufferSize
             << ')' << endl;
+
+        if (maxThreadFileBufferSize == 0)
+        {
+            Info<< "         Threading not activated "
+                   "since maxThreadFileBufferSize = 0." << nl
+                << "         Writing may run slowly for large file sizes."
+                << endl;
+        }
+        else
+        {
+            Info<< "         Threading activated "
+                   "since maxThreadFileBufferSize > 0." << nl
+                << "         Requires thread support enabled in MPI, "
+                   "otherwise the simulation" << nl
+                << "         may \"hang\".  If thread support cannot be "
+                   "enabled, deactivate threading" << nl
+                << "         by setting maxThreadFileBufferSize to 0 in "
+                   "$FOAM_ETC/controlDict"
+                << endl;
+        }
+
         if
         (
             regIOobject::fileModificationChecking
@@ -192,6 +213,7 @@ Foam::fileOperations::collatedFileOperation::collatedFileOperation
             WarningInFunction
                 << "Resetting fileModificationChecking to inotify" << endl;
         }
+
         if
         (
             regIOobject::fileModificationChecking