We were accessing the ModuleList in the target without locking it for tasks like

setting breakpoints.  That's dangerous, since while we are setting a breakpoint,
the target might hit the dyld load notification, and start removing modules from
the list.  This change adds a GetMutex accessor to the ModuleList class, and
uses it whenever we are accessing the target's ModuleList (as returned by GetImages().)

<rdar://problem/11552372>

llvm-svn: 157668

12 files changed, 152 insertions, 54 deletions

diff --git a/lldb/include/lldb/Core/ModuleList.h b/lldb/include/lldb/Core/ModuleList.h
index c3b9a637bc0..e1551f94c50 100644
--- a/lldb/include/lldb/Core/ModuleList.h
+++ b/lldb/include/lldb/Core/ModuleList.h
@@ -116,6 +116,13 @@ public:
     LogUUIDAndPaths (lldb::LogSP &log_sp, 
                      const char *prefix_cstr);
 
+
+    Mutex &
+    GetMutex ()
+    {
+        return m_modules_mutex;
+    }
+    
     uint32_t
     GetIndexForModule (const Module *module) const;
 
@@ -135,6 +142,23 @@ public:
     GetModuleAtIndex (uint32_t idx);
 
     //------------------------------------------------------------------
+    /// Get the module shared pointer for the module at index \a idx without
+    /// acquiring the ModuleList mutex.  This MUST already have been 
+    /// acquired with ModuleList::GetMutex and locked for this call to be safe.
+    ///
+    /// @param[in] idx
+    ///     An index into this module collection.
+    ///
+    /// @return
+    ///     A shared pointer to a Module which can contain NULL if
+    ///     \a idx is out of range.
+    ///
+    /// @see ModuleList::GetSize()
+    //------------------------------------------------------------------
+    lldb::ModuleSP
+    GetModuleAtIndexUnlocked (uint32_t idx);
+
+    //------------------------------------------------------------------
     /// Get the module pointer for the module at index \a idx.
     ///
     /// @param[in] idx
@@ -150,6 +174,23 @@ public:
     GetModulePointerAtIndex (uint32_t idx) const;
 
     //------------------------------------------------------------------
+    /// Get the module pointer for the module at index \a idx without
+    /// acquiring the ModuleList mutex.  This MUST already have been 
+    /// acquired with ModuleList::GetMutex and locked for this call to be safe.
+    ///
+    /// @param[in] idx
+    ///     An index into this module collection.
+    ///
+    /// @return
+    ///     A pointer to a Module which can by NULL if \a idx is out
+    ///     of range.
+    ///
+    /// @see ModuleList::GetSize()
+    //------------------------------------------------------------------
+    Module*
+    GetModulePointerAtIndexUnlocked (uint32_t idx) const;
+
+    //------------------------------------------------------------------
     /// Find compile units by partial or full path.
     ///
     /// Finds all compile units that match \a path in all of the modules
diff --git a/lldb/source/Breakpoint/Breakpoint.cpp b/lldb/source/Breakpoint/Breakpoint.cpp
index 5d0cbd47e20..789118b3a40 100644
--- a/lldb/source/Breakpoint/Breakpoint.cpp
+++ b/lldb/source/Breakpoint/Breakpoint.cpp
@@ -317,6 +317,7 @@ Breakpoint::ClearAllBreakpointSites ()
 void
 Breakpoint::ModulesChanged (ModuleList &module_list, bool load, bool delete_locations)
 {
+    Mutex::Locker modules_mutex(module_list.GetMutex());
     if (load)
     {
         // The logic for handling new modules is:
@@ -332,11 +333,11 @@ Breakpoint::ModulesChanged (ModuleList &module_list, bool load, bool delete_loca
                                  // resolving breakpoints will add new locations potentially.
 
         const size_t num_locs = m_locations.GetSize();
-
-        for (size_t i = 0; i < module_list.GetSize(); i++)
+        size_t num_modules = module_list.GetSize();
+        for (size_t i = 0; i < num_modules; i++)
         {
             bool seen = false;
-            ModuleSP module_sp (module_list.GetModuleAtIndex (i));
+            ModuleSP module_sp (module_list.GetModuleAtIndexUnlocked (i));
             if (!m_filter_sp->ModulePasses (module_sp))
                 continue;
 
@@ -403,10 +404,11 @@ Breakpoint::ModulesChanged (ModuleList &module_list, bool load, bool delete_loca
                                                                shared_from_this());
         else
             removed_locations_event = NULL;
-                    
-        for (size_t i = 0; i < module_list.GetSize(); i++)
+        
+        size_t num_modules = module_list.GetSize();
+        for (size_t i = 0; i < num_modules; i++)
         {
-            ModuleSP module_sp (module_list.GetModuleAtIndex (i));
+            ModuleSP module_sp (module_list.GetModuleAtIndexUnlocked (i));
             if (m_filter_sp->ModulePasses (module_sp))
             {
                 size_t loc_idx = 0;
diff --git a/lldb/source/Commands/CommandObjectTarget.cpp b/lldb/source/Commands/CommandObjectTarget.cpp
index a38f143eb22..c5987eef539 100644
--- a/lldb/source/Commands/CommandObjectTarget.cpp
+++ b/lldb/source/Commands/CommandObjectTarget.cpp
@@ -1882,6 +1882,7 @@ public:
             if (command.GetArgumentCount() == 0)
             {
                 // Dump all sections for all modules images
+                Mutex::Locker modules_locker(target->GetImages().GetMutex());
                 const uint32_t num_modules = target->GetImages().GetSize();
                 if (num_modules > 0)
                 {
@@ -1894,7 +1895,10 @@ public:
                             result.GetOutputStream().EOL();
                         }
                         num_dumped++;
-                        DumpModuleSymtab (m_interpreter, result.GetOutputStream(), target->GetImages().GetModulePointerAtIndex(image_idx), m_options.m_sort_order);
+                        DumpModuleSymtab (m_interpreter,
+                                          result.GetOutputStream(),
+                                          target->GetImages().GetModulePointerAtIndexUnlocked(image_idx),
+                                          m_options.m_sort_order);
                     }
                 }
                 else
@@ -2179,13 +2183,15 @@ public:
             if (command.GetArgumentCount() == 0)
             {
                 // Dump all sections for all modules images
-                const uint32_t num_modules = target->GetImages().GetSize();
+                ModuleList &target_modules = target->GetImages();
+                Mutex::Locker modules_locker (target_modules.GetMutex());
+                const uint32_t num_modules = target_modules.GetSize();
                 if (num_modules > 0)
                 {
                     result.GetOutputStream().Printf("Dumping debug symbols for %u modules.\n", num_modules);
                     for (uint32_t image_idx = 0;  image_idx<num_modules; ++image_idx)
                     {
-                        if (DumpModuleSymbolVendor (result.GetOutputStream(), target->GetImages().GetModulePointerAtIndex(image_idx)))
+                        if (DumpModuleSymbolVendor (result.GetOutputStream(), target_modules.GetModulePointerAtIndexUnlocked(image_idx)))
                             num_dumped++;
                     }
                 }
@@ -2288,7 +2294,10 @@ public:
                 for (int arg_idx = 0; (arg_cstr = command.GetArgumentAtIndex(arg_idx)) != NULL; ++arg_idx)
                 {
                     FileSpec file_spec(arg_cstr, false);
-                    const uint32_t num_modules = target->GetImages().GetSize();
+                    
+                    ModuleList &target_modules = target->GetImages();
+                    Mutex::Locker modules_locker(target_modules.GetMutex());
+                    const uint32_t num_modules = target_modules.GetSize();
                     if (num_modules > 0)
                     {
                         uint32_t num_dumped = 0;
@@ -2296,7 +2305,7 @@ public:
                         {
                             if (DumpCompileUnitLineTable (m_interpreter,
                                                           result.GetOutputStream(),
-                                                          target->GetImages().GetModulePointerAtIndex(i),
+                                                          target_modules.GetModulePointerAtIndexUnlocked(i),
                                                           file_spec,
                                                           exe_ctx.GetProcessPtr() && exe_ctx.GetProcessRef().IsAlive()))
                                 num_dumped++;
@@ -2807,9 +2816,6 @@ public:
                 result.GetErrorStream().SetAddressByteSize(addr_byte_size);
             }
             // Dump all sections for all modules images
-            uint32_t num_modules = 0;
-            Mutex::Locker locker;
-            
             Stream &strm = result.GetOutputStream();
             
             if (m_options.m_module_addr != LLDB_INVALID_ADDRESS)
@@ -2845,6 +2851,11 @@ public:
                 return result.Succeeded();
             }
             
+            uint32_t num_modules = 0;
+            Mutex::Locker locker;      // This locker will be locked on the mutex in module_list_ptr if it is non-NULL.
+                                       // Otherwise it will lock the AllocationModuleCollectionMutex when accessing
+                                       // the global module list directly.
+            
             ModuleList module_list;
             ModuleList *module_list_ptr = NULL;
             const size_t argc = command.GetArgumentCount();
@@ -2858,7 +2869,6 @@ public:
                 else
                 {
                     module_list_ptr = &target->GetImages();
-                    num_modules = target->GetImages().GetSize();
                 }
             }
             else
@@ -2879,9 +2889,14 @@ public:
                     }
                 }
                 
-                num_modules = module_list.GetSize();
                 module_list_ptr = &module_list;
             }
+            
+            if (module_list_ptr != NULL)
+            {
+                locker.Lock(module_list_ptr->GetMutex());
+                num_modules = module_list_ptr->GetSize();
+            }
 
             if (num_modules > 0)
             {                
@@ -2891,7 +2906,7 @@ public:
                     Module *module;
                     if (module_list_ptr)
                     {
-                        module_sp = module_list_ptr->GetModuleAtIndex(image_idx);
+                        module_sp = module_list_ptr->GetModuleAtIndexUnlocked(image_idx);
                         module = module_sp.get();
                     }
                     else
@@ -3414,12 +3429,14 @@ public:
             if (command.GetArgumentCount() == 0)
             {
                 // Dump all sections for all modules images
-                const uint32_t num_modules = target->GetImages().GetSize();
+                ModuleList &target_modules = target->GetImages();
+                Mutex::Locker modules_locker(target_modules.GetMutex());
+                const uint32_t num_modules = target_modules.GetSize();
                 if (num_modules > 0)
                 {
                     for (i = 0; i<num_modules && syntax_error == false; ++i)
                     {
-                        if (LookupInModule (m_interpreter, target->GetImages().GetModulePointerAtIndex(i), result, syntax_error))
+                        if (LookupInModule (m_interpreter, target_modules.GetModulePointerAtIndexUnlocked(i), result, syntax_error))
                         {
                             result.GetOutputStream().EOL();
                             num_successful_lookups++;
diff --git a/lldb/source/Core/ModuleList.cpp b/lldb/source/Core/ModuleList.cpp
index 8f852d4d8d1..157dafa7a2c 100644
--- a/lldb/source/Core/ModuleList.cpp
+++ b/lldb/source/Core/ModuleList.cpp
@@ -201,6 +201,12 @@ Module*
 ModuleList::GetModulePointerAtIndex (uint32_t idx) const
 {
     Mutex::Locker locker(m_modules_mutex);
+    return GetModulePointerAtIndexUnlocked(idx);
+}
+
+Module*
+ModuleList::GetModulePointerAtIndexUnlocked (uint32_t idx) const
+{
     if (idx < m_modules.size())
         return m_modules[idx].get();
     return NULL;
@@ -210,6 +216,12 @@ ModuleSP
 ModuleList::GetModuleAtIndex(uint32_t idx)
 {
     Mutex::Locker locker(m_modules_mutex);
+    return GetModuleAtIndexUnlocked(idx);
+}
+
+ModuleSP
+ModuleList::GetModuleAtIndexUnlocked(uint32_t idx)
+{
     ModuleSP module_sp;
     if (idx < m_modules.size())
         module_sp = m_modules[idx];
diff --git a/lldb/source/Core/SearchFilter.cpp b/lldb/source/Core/SearchFilter.cpp
index b52ffdd24b0..f00f222bc30 100644
--- a/lldb/source/Core/SearchFilter.cpp
+++ b/lldb/source/Core/SearchFilter.cpp
@@ -160,11 +160,12 @@ SearchFilter::SearchInModuleList (Searcher &searcher, ModuleList &modules)
         searcher.SearchCallback (*this, empty_sc, NULL, false);
     else
     {
+        Mutex::Locker modules_locker(modules.GetMutex());
         const size_t numModules = modules.GetSize();
 
         for (size_t i = 0; i < numModules; i++)
         {
-            ModuleSP module_sp(modules.GetModuleAtIndex(i));
+            ModuleSP module_sp(modules.GetModuleAtIndexUnlocked(i));
             if (ModulePasses(module_sp))
             {
                 if (DoModuleIteration(module_sp, searcher) == Searcher::eCallbackReturnStop)
@@ -191,12 +192,15 @@ SearchFilter::DoModuleIteration (const SymbolContext &context, Searcher &searche
     {
         if (!context.module_sp)
         {
-            size_t n_modules = m_target_sp->GetImages().GetSize();
+            ModuleList &target_images = m_target_sp->GetImages();
+            Mutex::Locker modules_locker(target_images.GetMutex());
+            
+            size_t n_modules = target_images.GetSize();
             for (size_t i = 0; i < n_modules; i++)
             {
                 // If this is the last level supplied, then call the callback directly,
                 // otherwise descend.
-                ModuleSP module_sp(m_target_sp->GetImages().GetModuleAtIndex(i));
+                ModuleSP module_sp(target_images.GetModuleAtIndexUnlocked (i));
                 if (!ModulePasses (module_sp))
                     continue;
 
@@ -427,11 +431,13 @@ SearchFilterByModule::Search (Searcher &searcher)
     // filespec that passes.  Otherwise, we need to go through all modules and
     // find the ones that match the file name.
 
-    ModuleList matching_modules;
-    const size_t num_modules = m_target_sp->GetImages().GetSize ();
+    ModuleList &target_modules = m_target_sp->GetImages();
+    Mutex::Locker modules_locker (target_modules.GetMutex());
+    
+    const size_t num_modules = target_modules.GetSize ();
     for (size_t i = 0; i < num_modules; i++)
     {
-        Module* module = m_target_sp->GetImages().GetModulePointerAtIndex(i);
+        Module* module = target_modules.GetModulePointerAtIndexUnlocked(i);
         if (FileSpec::Compare (m_module_spec, module->GetFileSpec(), false) == 0)
         {
             SymbolContext matchingContext(m_target_sp, module->shared_from_this());
@@ -591,11 +597,13 @@ SearchFilterByModuleList::Search (Searcher &searcher)
     // filespec that passes.  Otherwise, we need to go through all modules and
     // find the ones that match the file name.
 
-    ModuleList matching_modules;
-    const size_t num_modules = m_target_sp->GetImages().GetSize ();
+    ModuleList &target_modules = m_target_sp->GetImages();
+    Mutex::Locker modules_locker (target_modules.GetMutex());
+    
+    const size_t num_modules = target_modules.GetSize ();
     for (size_t i = 0; i < num_modules; i++)
     {
-        Module* module = m_target_sp->GetImages().GetModulePointerAtIndex(i);
+        Module* module = target_modules.GetModulePointerAtIndexUnlocked(i);
         if (m_module_spec_list.FindFileIndex(0, module->GetFileSpec(), false) != UINT32_MAX)
         {
             SymbolContext matchingContext(m_target_sp, module->shared_from_this());
@@ -762,11 +770,14 @@ SearchFilterByModuleListAndCU::Search (Searcher &searcher)
     // find the ones that match the file name.
 
     ModuleList matching_modules;
-    const size_t num_modules = m_target_sp->GetImages().GetSize ();
+    ModuleList &target_images = m_target_sp->GetImages();
+    Mutex::Locker modules_locker(target_images.GetMutex());
+    
+    const size_t num_modules = target_images.GetSize ();
     bool no_modules_in_filter = m_module_spec_list.GetSize() == 0;
     for (size_t i = 0; i < num_modules; i++)
     {
-        lldb::ModuleSP module_sp = m_target_sp->GetImages().GetModuleAtIndex(i);
+        lldb::ModuleSP module_sp = target_images.GetModuleAtIndexUnlocked(i);
         if (no_modules_in_filter || m_module_spec_list.FindFileIndex(0, module_sp->GetFileSpec(), false) != UINT32_MAX)
         {
             SymbolContext matchingContext(m_target_sp, module_sp);
diff --git a/lldb/source/Expression/ClangASTSource.cpp b/lldb/source/Expression/ClangASTSource.cpp
index 4c31c223b89..605747adb56 100644
--- a/lldb/source/Expression/ClangASTSource.cpp
+++ b/lldb/source/Expression/ClangASTSource.cpp
@@ -561,13 +561,14 @@ ClangASTSource::FindExternalVisibleDecls (NameSearchContext &context,
     }
     else 
     {
-        ModuleList &images = m_target->GetImages();
+        ModuleList &target_images = m_target->GetImages();
+        Mutex::Locker modules_locker (target_images.GetMutex());
         
-        for (uint32_t i = 0, e = images.GetSize();
+        for (uint32_t i = 0, e = target_images.GetSize();
              i != e;
              ++i)
         {
-            lldb::ModuleSP image = images.GetModuleAtIndex(i);
+            lldb::ModuleSP image = target_images.GetModuleAtIndexUnlocked(i);
             
             if (!image)
                 continue;
@@ -1339,14 +1340,16 @@ ClangASTSource::CompleteNamespaceMap (ClangASTImporter::NamespaceMapSP &namespac
     }
     else
     {
-        ModuleList &images = m_target->GetImages();
+        ModuleList &target_images = m_target->GetImages();
+        Mutex::Locker modules_locker(target_images.GetMutex());
+        
         ClangNamespaceDecl null_namespace_decl;
         
-        for (uint32_t i = 0, e = images.GetSize();
+        for (uint32_t i = 0, e = target_images.GetSize();
              i != e;
              ++i)
         {
-            lldb::ModuleSP image = images.GetModuleAtIndex(i);
+            lldb::ModuleSP image = target_images.GetModuleAtIndexUnlocked(i);
             
             if (!image)
                 continue;
diff --git a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderMacOSXDYLD.cpp b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderMacOSXDYLD.cpp
index c8e9cec70c5..c42f469fea6 100644
--- a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderMacOSXDYLD.cpp
+++ b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderMacOSXDYLD.cpp
@@ -1057,12 +1057,14 @@ DynamicLoaderMacOSXDYLD::InitializeFromAllImageInfos ()
         // to an equivalent version.  We don't want it to stay in the target's module list or it will confuse
         // us, so unload it here.
         Target &target = m_process->GetTarget();
-        ModuleList &modules = target.GetImages();
+        ModuleList &target_modules = target.GetImages();
         ModuleList not_loaded_modules;
-        size_t num_modules = modules.GetSize();
+        Mutex::Locker modules_locker(target_modules.GetMutex());
+        
+        size_t num_modules = target_modules.GetSize();
         for (size_t i = 0; i < num_modules; i++)
         {
-            ModuleSP module_sp = modules.GetModuleAtIndex(i);
+            ModuleSP module_sp = target_modules.GetModuleAtIndexUnlocked (i);
             if (!module_sp->IsLoadedInTarget (&target))
             {
                 if (log)
diff --git a/lldb/source/Plugins/DynamicLoader/Static/DynamicLoaderStatic.cpp b/lldb/source/Plugins/DynamicLoader/Static/DynamicLoaderStatic.cpp
index a1d64422e60..abfbf1c9ab6 100644
--- a/lldb/source/Plugins/DynamicLoader/Static/DynamicLoaderStatic.cpp
+++ b/lldb/source/Plugins/DynamicLoader/Static/DynamicLoaderStatic.cpp
@@ -97,10 +97,12 @@ DynamicLoaderStatic::LoadAllImagesAtFileAddresses ()
     
     ModuleList loaded_module_list;
 
+    Mutex::Locker mutex_locker(module_list.GetMutex());
+    
     const size_t num_modules = module_list.GetSize();
     for (uint32_t idx = 0; idx < num_modules; ++idx)
     {
-        ModuleSP module_sp (module_list.GetModuleAtIndex (idx));
+        ModuleSP module_sp (module_list.GetModuleAtIndexUnlocked (idx));
         if (module_sp)
         {
             bool changed = false;
diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.cpp
index 1cb7ab8eef9..a2bc88872c1 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.cpp
@@ -263,11 +263,13 @@ AppleObjCRuntime::GetObjCVersion (Process *process, ModuleSP &objc_module_sp)
         return eObjC_VersionUnknown;
         
     Target &target = process->GetTarget();
-    ModuleList &images = target.GetImages();
-    size_t num_images = images.GetSize();
+    ModuleList &target_modules = target.GetImages();
+    Mutex::Locker modules_locker(target_modules.GetMutex());
+    
+    size_t num_images = target_modules.GetSize();
     for (size_t i = 0; i < num_images; i++)
     {
-        ModuleSP module_sp = images.GetModuleAtIndex(i);
+        ModuleSP module_sp = target_modules.GetModuleAtIndexUnlocked(i);
         // One tricky bit here is that we might get called as part of the initial module loading, but
         // before all the pre-run libraries get winnowed from the module list.  So there might actually
         // be an old and incorrect ObjC library sitting around in the list, and we don't want to look at that.
diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCSymbolVendor.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCSymbolVendor.cpp
index ff135806f28..00c90c6eacd 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCSymbolVendor.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCSymbolVendor.cpp
@@ -43,13 +43,14 @@ AppleObjCSymbolVendor::FindTypes (const SymbolContext& sc,
     
     uint32_t ret = 0;
     
-    ModuleList &images = m_process->GetTarget().GetImages();
+    ModuleList &target_modules = m_process->GetTarget().GetImages();
+    Mutex::Locker modules_locker(target_modules.GetMutex());
     
-    for (size_t image_index = 0, end_index = images.GetSize();
+    for (size_t image_index = 0, end_index = target_modules.GetSize();
          image_index < end_index;
          ++image_index)
     {
-        Module *image = images.GetModulePointerAtIndex(image_index);
+        Module *image = target_modules.GetModulePointerAtIndexUnlocked(image_index);
         
         if (!image)
             continue;
diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.cpp
index f8cab06732d..54eda8bddf5 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.cpp
@@ -334,15 +334,16 @@ AppleObjCTrampolineHandler::AppleObjCVTables::InitializeVTableSymbols ()
         return true;
     Target &target = m_process_sp->GetTarget();
     
-    ModuleList &modules = target.GetImages();
-    size_t num_modules = modules.GetSize();
+    ModuleList &target_modules = target.GetImages();
+    Mutex::Locker modules_locker(target_modules.GetMutex());
+    size_t num_modules = target_modules.GetSize();
     if (!m_objc_module_sp)
     {
         for (size_t i = 0; i < num_modules; i++)
         {
-            if (m_process_sp->GetObjCLanguageRuntime()->IsModuleObjCLibrary (modules.GetModuleAtIndex(i)))
+            if (m_process_sp->GetObjCLanguageRuntime()->IsModuleObjCLibrary (target_modules.GetModuleAtIndexUnlocked(i)))
             {
-                m_objc_module_sp = modules.GetModuleAtIndex(i);
+                m_objc_module_sp = target_modules.GetModuleAtIndexUnlocked(i);
                 break;
             }
         }
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index 832feaac9ae..64626a97a7e 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -2814,19 +2814,23 @@ Process::CompleteAttach ()
 
     m_os_ap.reset (OperatingSystem::FindPlugin (this, NULL));
     // Figure out which one is the executable, and set that in our target:
-    ModuleList &modules = m_target.GetImages();
+    ModuleList &target_modules = m_target.GetImages();
+    Mutex::Locker modules_locker(target_modules.GetMutex());
+    size_t num_modules = target_modules.GetSize();
+    ModuleSP new_executable_module_sp;
     
-    size_t num_modules = modules.GetSize();
     for (int i = 0; i < num_modules; i++)
     {
-        ModuleSP module_sp (modules.GetModuleAtIndex(i));
+        ModuleSP module_sp (target_modules.GetModuleAtIndexUnlocked (i));
         if (module_sp && module_sp->IsExecutable())
         {
             if (m_target.GetExecutableModulePointer() != module_sp.get())
-                m_target.SetExecutableModule (module_sp, false);
+                new_executable_module_sp = module_sp;
             break;
         }
     }
+    if (new_executable_module_sp)
+        m_target.SetExecutableModule (new_executable_module_sp, false);
 }
 
 Error