Index: include/lldb/Symbol/SymbolFile.h
===================================================================
--- include/lldb/Symbol/SymbolFile.h
+++ include/lldb/Symbol/SymbolFile.h
@@ -203,6 +203,8 @@
   virtual void Dump(Stream &s) {}
 
 protected:
+  void AssertModuleLock();
+
   ObjectFile *m_obj_file; // The object file that symbols can be extracted from.
   uint32_t m_abilities;
   bool m_calculated_abilities;
Index: source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -262,6 +262,7 @@
 }
 
 TypeList *SymbolFileDWARF::GetTypeList() {
+  AssertModuleLock();
   SymbolFileDWARFDebugMap *debug_map_symfile = GetDebugMapSymfile();
   if (debug_map_symfile)
     return debug_map_symfile->GetTypeList();
@@ -343,6 +344,7 @@
                                  uint32_t type_mask, TypeList &type_list)
 
 {
+  AssertModuleLock();
   TypeSet type_set;
 
   CompileUnit *comp_unit = NULL;
@@ -854,6 +856,7 @@
 }
 
 CompUnitSP SymbolFileDWARF::ParseCompileUnitAtIndex(uint32_t cu_idx) {
+  AssertModuleLock();
   CompUnitSP cu_sp;
   DWARFDebugInfo *info = DebugInfo();
   if (info) {
@@ -866,6 +869,7 @@
 
 Function *SymbolFileDWARF::ParseCompileUnitFunction(const SymbolContext &sc,
                                                     const DWARFDIE &die) {
+  AssertModuleLock();
   if (die.IsValid()) {
     TypeSystem *type_system =
         GetTypeSystemForLanguage(die.GetCU()->GetLanguageType());
@@ -889,6 +893,7 @@
 }
 lldb::LanguageType
 SymbolFileDWARF::ParseCompileUnitLanguage(const SymbolContext &sc) {
+  AssertModuleLock();
   assert(sc.comp_unit);
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
   if (dwarf_cu)
@@ -898,6 +903,7 @@
 }
 
 size_t SymbolFileDWARF::ParseCompileUnitFunctions(const SymbolContext &sc) {
+  AssertModuleLock();
   assert(sc.comp_unit);
   size_t functions_added = 0;
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
@@ -920,6 +926,7 @@
 
 bool SymbolFileDWARF::ParseCompileUnitSupportFiles(
     const SymbolContext &sc, FileSpecList &support_files) {
+  AssertModuleLock();
   assert(sc.comp_unit);
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
   if (dwarf_cu) {
@@ -945,6 +952,7 @@
 
 bool SymbolFileDWARF::ParseCompileUnitIsOptimized(
     const lldb_private::SymbolContext &sc) {
+  AssertModuleLock();
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
   if (dwarf_cu)
     return dwarf_cu->GetIsOptimized();
@@ -954,6 +962,7 @@
 bool SymbolFileDWARF::ParseImportedModules(
     const lldb_private::SymbolContext &sc,
     std::vector<lldb_private::ConstString> &imported_modules) {
+  AssertModuleLock();
   assert(sc.comp_unit);
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
   if (dwarf_cu) {
@@ -1031,6 +1040,7 @@
 }
 
 bool SymbolFileDWARF::ParseCompileUnitLineTable(const SymbolContext &sc) {
+  AssertModuleLock();
   assert(sc.comp_unit);
   if (sc.comp_unit->GetLineTable() != NULL)
     return true;
@@ -1116,6 +1126,7 @@
 }
 
 bool SymbolFileDWARF::ParseCompileUnitDebugMacros(const SymbolContext &sc) {
+  AssertModuleLock();
   assert(sc.comp_unit);
 
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
@@ -1295,6 +1306,8 @@
 }
 
 SymbolFileDWARF *SymbolFileDWARF::GetDWARFForUID(lldb::user_id_t uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we get a "lldb::user_id_t" from an lldb_private::SymbolFile API we
   // must make sure we use the correct DWARF file when resolving things. On
   // MacOSX, when using SymbolFileDWARFDebugMap, we will use multiple
@@ -1311,6 +1324,8 @@
 
 DWARFDIE
 SymbolFileDWARF::GetDIEFromUID(lldb::user_id_t uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we get a "lldb::user_id_t" from an lldb_private::SymbolFile API we
   // must make sure we use the correct DWARF file when resolving things. On
   // MacOSX, when using SymbolFileDWARFDebugMap, we will use multiple
@@ -1325,6 +1340,8 @@
 }
 
 CompilerDecl SymbolFileDWARF::GetDeclForUID(lldb::user_id_t type_uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we have a lldb::user_id_t, we must get the DIE by calling
   // SymbolFileDWARF::GetDIEFromUID(). See comments inside the
   // SymbolFileDWARF::GetDIEFromUID() for details.
@@ -1336,6 +1353,8 @@
 
 CompilerDeclContext
 SymbolFileDWARF::GetDeclContextForUID(lldb::user_id_t type_uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we have a lldb::user_id_t, we must get the DIE by calling
   // SymbolFileDWARF::GetDIEFromUID(). See comments inside the
   // SymbolFileDWARF::GetDIEFromUID() for details.
@@ -1347,6 +1366,8 @@
 
 CompilerDeclContext
 SymbolFileDWARF::GetDeclContextContainingUID(lldb::user_id_t type_uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we have a lldb::user_id_t, we must get the DIE by calling
   // SymbolFileDWARF::GetDIEFromUID(). See comments inside the
   // SymbolFileDWARF::GetDIEFromUID() for details.
@@ -1357,6 +1378,8 @@
 }
 
 Type *SymbolFileDWARF::ResolveTypeUID(lldb::user_id_t type_uid) {
+  std::lock_guard<std::recursive_mutex> guard(
+      GetObjectFile()->GetModule()->GetMutex());
   // Anytime we have a lldb::user_id_t, we must get the DIE by calling
   // SymbolFileDWARF::GetDIEFromUID(). See comments inside the
   // SymbolFileDWARF::GetDIEFromUID() for details.
@@ -3069,6 +3092,7 @@
 }
 
 size_t SymbolFileDWARF::ParseFunctionBlocks(const SymbolContext &sc) {
+  AssertModuleLock();
   assert(sc.comp_unit && sc.function);
   size_t functions_added = 0;
   DWARFUnit *dwarf_cu = GetDWARFCompileUnit(sc.comp_unit);
@@ -3085,6 +3109,7 @@
 }
 
 size_t SymbolFileDWARF::ParseTypes(const SymbolContext &sc) {
+  AssertModuleLock();
   // At least a compile unit must be valid
   assert(sc.comp_unit);
   size_t types_added = 0;
@@ -3108,6 +3133,7 @@
 }
 
 size_t SymbolFileDWARF::ParseVariablesForContext(const SymbolContext &sc) {
+  AssertModuleLock();
   if (sc.comp_unit != NULL) {
     DWARFDebugInfo *info = DebugInfo();
     if (info == NULL)
Index: source/Symbol/SymbolFile.cpp
===================================================================
--- source/Symbol/SymbolFile.cpp
+++ source/Symbol/SymbolFile.cpp
@@ -19,6 +19,8 @@
 #include "lldb/Utility/StreamString.h"
 #include "lldb/lldb-private.h"
 
+#include <future>
+
 using namespace lldb_private;
 
 void SymbolFile::PreloadSymbols() {
@@ -150,3 +152,16 @@
     types.Clear();
   return 0;
 }
+
+void SymbolFile::AssertModuleLock() {
+  // We assert that we have to module lock by trying to acquire the lock from a
+  // different thread. Note that we must abort if the result is true to
+  // guarantee correctness.
+  assert(std::async(
+             std::launch::async,
+             [this] {
+               return this->GetObjectFile()->GetModule()->GetMutex().try_lock();
+             })
+                 .get() == false &&
+         "Module is not locked");
+}