Don't lock for the duration fo GetDependentModules

Author: JDevlieghere

lldb/source/Target/Target.cpp

@@ -1613,8 +1613,28 @@ void Target::SetExecutableModule(ModuleSP &executable_sp,
           added_modules.AppendIfNeeded(image_module_sp, false);
           ObjectFile *objfile = image_module_sp->GetObjectFile();
           if (objfile) {
-            std::lock_guard<std::mutex> guard(dependent_files_mutex);
-            objfile->GetDependentModules(dependent_files);
+            // Create a local copy of the dependent file list so we don't have
+            // to lock for the whole duration of GetDependentModules.
+            FileSpecList dependent_files_copy;
+            {
+              std::lock_guard<std::mutex> guard(dependent_files_mutex);
+              dependent_files_copy = dependent_files;
+            }
+
+            // Remember the size of the local copy so we can append only the
+            // modules that have been added by GetDependentModules.
+            const size_t previous_dependent_files =
+                dependent_files_copy.GetSize();
+
+            objfile->GetDependentModules(dependent_files_copy);
+
+            {
+              std::lock_guard<std::mutex> guard(dependent_files_mutex);
+              for (size_t i = previous_dependent_files;
+                   i < dependent_files_copy.GetSize(); ++i)
+                dependent_files.AppendIfUnique(
+                    dependent_files_copy.GetFileSpecAtIndex(i));
+            }
           }
         }
       };