Workaround for wxString's lack of thread safety.

pcbnew/board_items_to_polygon_shape_transform.cpp

@@ -405,6 +405,10 @@ void TEXTE_PCB::TransformBoundingBoxWithClearanceToPolygon(
                     SHAPE_POLY_SET& aCornerBuffer,
                     int             aClearanceValue ) const
 {
+    // Oh dear.  When in UTF-8 mode, wxString puts string iterators in a linked list, and
+    // that linked list is not thread-safe.
+    std::lock_guard<std::mutex> guard( m_mutex );
+
     if( GetText().Length() == 0 )
         return;
 

pcbnew/class_pcb_text.h

@@ -40,6 +40,17 @@ class EDA_DRAW_PANEL;
 class MSG_PANEL_ITEM;
 
 
+// A mutex which is unique to each instance it appears in (ie: a new std::mutex is allocated
+// on copy or assignment).
+class UNIQUE_MUTEX : public std::mutex
+{
+public:
+    UNIQUE_MUTEX() : std::mutex() {}
+    UNIQUE_MUTEX( const UNIQUE_MUTEX& ) : std::mutex() {}
+    UNIQUE_MUTEX& operator= (const UNIQUE_MUTEX& ) { return *this; }
+};
+
+
 class TEXTE_PCB : public BOARD_ITEM, public EDA_TEXT
 {
 public:
@@ -142,6 +153,8 @@ public:
 
     virtual void SwapData( BOARD_ITEM* aImage ) override;
 
+    mutable UNIQUE_MUTEX m_mutex;
+
 #if defined(DEBUG)
     virtual void Show( int nestLevel, std::ostream& os ) const override { ShowDummy( os ); }
 #endif