From 07069d7119b7e83fb079ff8924a1615311986c4f Mon Sep 17 00:00:00 2001
From: Denis Davydov <davydden@gmail.com>
Date: Tue, 30 Oct 2018 16:52:48 +0100
Subject: [PATCH] add mutex lock

---
 source/base/incremental_function.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/source/base/incremental_function.cc b/source/base/incremental_function.cc
index 49bde1148c..18091c358d 100644
--- a/source/base/incremental_function.cc
+++ b/source/base/incremental_function.cc
@@ -50,6 +50,10 @@ namespace Functions
     const Point<dim> & p,
     const unsigned int comp) const
   {
+    // since we modify a mutable member variable, lock the
+    // the data via a mutex
+    std::lock_guard<std::mutex> lock(mutex);
+
     // Cache the time state of the base class in case it has been changed
     // within the user code. We reset the wrapped function to the original
     // state once we're done with our own evaluations.
-- 
2.39.5