Guard all uses of basic_random_generator for thread safety

src/Mod/TechDraw/App/Geometry.cpp

@@ -81,6 +81,8 @@
 #include <Base/Reader.h>
 #include <Base/Tools.h>
 #include <Base/Writer.h>
+#include <boost/thread/mutex.hpp>
+#include <boost/thread/thread.hpp>
 
 #include <Mod/Part/App/Geometry.h>
 #include <Mod/Part/App/TopoShape.h>
@@ -1393,9 +1395,13 @@ void Vertex::Restore(Base::XMLReader &reader)
 void Vertex::createNewTag()
 {
     // Initialize a random number generator, to avoid Valgrind false positives.
+    // The random number generator is not threadsafe so we guard it.  See
+    // https://www.boost.org/doc/libs/1_62_0/libs/uuid/uuid.html#Design%20notes
     static boost::mt19937 ran;
     static bool seeded = false;
+    static boost::mutex random_number_mutex;
 
+    boost::lock_guard<boost::mutex> guard(random_number_mutex);
     if (!seeded) {
         ran.seed(static_cast<unsigned int>(std::time(nullptr)));
         seeded = true;