Merge branch 'fix_async_load' into 'master'

Fix crash related to async content loading (#7508)

Closes #7508

See merge request OpenMW/openmw!3290

components/CMakeLists.txt

@@ -292,7 +292,7 @@ add_component_dir (terrain
     )
 
 add_component_dir (loadinglistener
-    loadinglistener
+    loadinglistener asynclistener
     )
 
 add_component_dir (myguiplatform

components/loadinglistener/asynclistener.hpp

@@ -0,0 +1,67 @@
+#ifndef COMPONENTS_LOADINGLISTENER_ASYNCLISTENER_H
+#define COMPONENTS_LOADINGLISTENER_ASYNCLISTENER_H
+
+#include <mutex>
+#include <optional>
+#include <string>
+
+#include "loadinglistener.hpp"
+
+namespace Loading
+{
+    class AsyncListener : public Listener
+    {
+    public:
+        AsyncListener(Listener& baseListener)
+            : mBaseListener(baseListener)
+        {
+        }
+
+        void setLabel(const std::string& label, bool important) override
+        {
+            std::lock_guard<std::mutex> guard(mMutex);
+            mLabelUpdate = label;
+            mImportantLabel = important;
+        }
+
+        void setProgressRange(size_t range) override
+        {
+            std::lock_guard<std::mutex> guard(mMutex);
+            mRangeUpdate = range;
+        }
+
+        void setProgress(size_t value) override
+        {
+            std::lock_guard<std::mutex> guard(mMutex);
+            mProgressUpdate = value;
+        }
+
+        void increaseProgress(size_t increase) override
+        { /* not implemented */
+        }
+
+        void update()
+        {
+            std::lock_guard<std::mutex> guard(mMutex);
+            if (mLabelUpdate)
+                mBaseListener.setLabel(*mLabelUpdate, mImportantLabel);
+            if (mRangeUpdate)
+                mBaseListener.setProgressRange(*mRangeUpdate);
+            if (mProgressUpdate)
+                mBaseListener.setProgress(*mProgressUpdate);
+            mLabelUpdate = std::nullopt;
+            mRangeUpdate = std::nullopt;
+            mProgressUpdate = std::nullopt;
+        }
+
+    private:
+        Listener& mBaseListener;
+        std::mutex mMutex;
+        std::optional<std::string> mLabelUpdate;
+        bool mImportantLabel = false;
+        std::optional<size_t> mRangeUpdate;
+        std::optional<size_t> mProgressUpdate;
+    };
+}
+
+#endif // COMPONENTS_LOADINGLISTENER_ASYNCLISTENER_H