Index: source/Plugins/SymbolFile/DWARF/DWARFUnit.h
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFUnit.h
+++ source/Plugins/SymbolFile/DWARF/DWARFUnit.h
@@ -13,6 +13,7 @@
 #include "DWARFDIE.h"
 #include "DWARFDebugInfoEntry.h"
 #include "lldb/lldb-enumerations.h"
+#include "llvm/Support/RWMutex.h"
 
 class DWARFUnit;
 class DWARFCompileUnit;
@@ -160,6 +161,7 @@
   // If this is a dwo compile unit this is the offset of the base compile unit
   // in the main object file
   dw_offset_t m_base_obj_offset = DW_INVALID_OFFSET;
+  llvm::sys::RWMutex m_extractdies_mutex;
 
   static void
   IndexPrivate(DWARFUnit *dwarf_cu, const lldb::LanguageType cu_language,
Index: source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -42,9 +42,20 @@
 // done.
 //----------------------------------------------------------------------
 size_t DWARFUnit::ExtractDIEsIfNeeded(bool cu_die_only) {
-  const size_t initial_die_array_size = m_die_array.size();
-  if ((cu_die_only && initial_die_array_size > 0) || initial_die_array_size > 1)
-    return 0; // Already parsed
+  size_t initial_die_array_size;
+  auto already_parsed = [cu_die_only, &initial_die_array_size, this]() -> bool {
+    initial_die_array_size = m_die_array.size();
+    return (cu_die_only && initial_die_array_size > 0)
+        || initial_die_array_size > 1;
+  };
+  {
+    llvm::sys::ScopedReader lock(m_extractdies_mutex);
+    if (already_parsed())
+      return 0;
+  }
+  llvm::sys::ScopedWriter lock(m_extractdies_mutex);
+  if (already_parsed())
+    return 0;
 
   static Timer::Category func_cat(LLVM_PRETTY_FUNCTION);
   Timer scoped_timer(
@@ -307,6 +318,8 @@
 
 void DWARFUnit::ClearDIEs(bool keep_compile_unit_die) {
   if (m_die_array.size() > 1) {
+    llvm::sys::ScopedWriter lock(m_extractdies_mutex);
+
     // std::vectors never get any smaller when resized to a smaller size,
     // or when clear() or erase() are called, the size will report that it
     // is smaller, but the memory allocated remains intact (call capacity()